Enginerding: How Are Seat Tube Angles Actually Measured & Why Does It Matter?

Jul 31, 2020
by Dan Roberts  


Words: Dan Roberts
Illustrations: Taj Mihelich




What is the seat tube angle?

Originally, the seat tube angle was one measurement along the axis of a bike's physical seat tube to the horizontal, measured in degrees. On many hardtail, road and gravel bikes this is still the case, as we have one straight tube from top to bottom.

On a side note, as a hardtail goes through its fork travel, the seat tube angle gets steeper. On a suspension bike the seat tube angle gets slacker as you go through the bike's travel. This is why hardtails can get away with seemingly slacker static angles in comparison to full suspension bikes.

A straight seat tube, pointing directly to the center of the bottom bracket means only one seat angle. This was the case for a long time, and on some bikes it still is.



Why do we have more than one on bikes?

As full suspension bikes became more popular, we had the problem of the wheel moving around and interfering with bits of the frame. Even with small diameter wheels and small amounts of travel the wheel or seat stay bridge could come into contact with the back of the seat tube.

The physical seat tube then needed to be moved away to create some clearance for the moving wheel and frame parts. But this meant the angle of the physical, or actual, seat tube and the angle to the center of the bottom bracket, our virtual seat tube angle, weren’t the same.

Some hardtails with large wheels and short chainstays also needed the seat tube to be moved out of the way to provide enough tire and mud clearance.

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With suspension travel and bigger wheels, that same straight to the BB seat tube we used to have would cause some issues. Engineers and designers had to move the physical tube out of the way to provide some clearance. And this is where we started to generate more than one seat angle and some confusion.



How do we measure the different ones?

Our current two seat tube angles are measured as follows.

The actual seat tube angle is pretty straight forward, measuring the angle to the horizontal of the actual seat tube tube.

The virtual, or sometimes called effective, seat tube angle is a little more difficult to visualise and is where our confusion and problems lie. It’s an angle measured from horizontal to the line from the center of the bottom bracket up to the intersection of the actual seat tube angle and the top of the head tube.

Our two seat angles, actual and virtual, are both measured from level with the top of the head tube. The actual is following the axis of our physical seat tube. The virtual points to the center of the bottom bracket. Both are measured from the horizontal.



What are the downsides to the current way of measuring?

The actual seat tube angle is a good measurement, but it only tells part of the story. The virtual seat tube angle, as it currently stands, is misleading and makes it difficult to compare bikes or even know if the one we are looking at on paper is going to fit us properly.

Most of us pedal our bike with the seat considerably higher than level with the top of the head tube. For example, I run a seat height of 820mm from the center of the BB, which is 144mm higher than the top of the Madonna V2 head tube.

We're rarely pedalling with our seat level with the top of the head tube. A more normal pedalling position is much higher, and so puts the seat further back and slackens our virtual seat tube angle in real life compared to the on-paper measurement.

The further we go above this imaginary line, the further back our seat goes and the slacker our virtual seat tube angle is in real life compared to the one on paper. Comparing bikes can also be tricky as two bikes on paper can have the same virtual seat tube angle but depending on their actual seat tube angle, and a few other factors, they can have drastically different seated positions.

The same is true of just one bike with multiple sizes. Often the virtual seat tube angle is the same for all sizes while the reality will be much different. Sometimes geometry tables only quote one seat tube angle without stating which one it is, leading to possibly more confusion.

With the same seat angles, as frame sizes grow and the rider's seat height gets higher and higher, the seat moves further back and slackens the virtual angle. As the front of the bike increases in length, the rider's weight falls further back between the two contact patches. Pointing the bike up a hill then means that their weight line could fall behind the rear contact patch and cause the rider to have to work extra hard to keep the bike in check on the uphills.



What could we implement to make measuring seat tube angles better?

Our current measuring system is a bit dated. Our modern suspension bikes have evolved a lot in recent years with the increased front centers, longer reaches and increased wheel size and travel.

Some of those factors help the seat tube positioning conundrum. A longer chain stay gives more room between the wheel and seat tube, whereas the longer dropper posts, with their increased insertion, have made packaging the now shorter seat tubes into the frame trickier.

We need to add a couple more measurements into the system to help paint the full picture of where our seat will be and make it easier to understand how our bike will fit us.

Adding in the seat height and offset from the BB to the actual seat tube angle give more information and make the virtual seat tube angle at that seat height match what we're riding in the real world.

Our actual seat tube angle is a good measurement, telling us the angle of the physical seat tube and the line along which our seat post or dropper will move.

Adding in the forward offset from the center of the BB to the actual seat tube angle gives us another side of the triangle and allows us to then calculate what our virtual seat tube angles will be for our actual seat heights. Although the trigonometry behind this is pretty involved, so there’s no easy formula to follow. Most of the time we can just draw it out in a CAD package and easily extract the angle.

There are a couple of ways of measuring this forward offset at the moment, with some using a horizontal measurement and others doing perpendicular to the seat tube.

The last, and probably most important step, is defining that seat height at which the virtual seat tube angle will be measured. The seat height is measured from the center of the BB along the virtual seat tube angle line to where it meets the actual seat tube angle line and is representative of where your seat will actually be when you’re pedalling.



Having worked with some of the tallest engineers in the industry (that's you French Dave), this stratospheric seat height isn't all that far fetched.


Is it difficult to understand?

On paper it sounds like a pain to figure this out, but some brands are already giving this information in their geometry.

Transition and Unno are two of the brands quoting the seat height at which they measure their virtual seat tube angle.

Unno currently only has one frame size available and so quote the angle for a seat height of 600mm, 650mm, 700mm and 750mm with the angle getting half a degree slacker as the seat height increases.

Transition, however, are giving out all the information. Actual seat tube angle, virtual seat tube angle, the seat height it’s measured at and also the offset from the BB. Transition use seat heights of 560mm, 600mm, 660mm, 720mm, 780mm and 820mmfor their XS, S, M, L, XL and XXL sizes respectively. Their actual seat tube angle remains the same for all sizes; as the seat height gets higher the virtual seat tube angle gets slacker.

As a rider, all you need to know is what seat height you use. And this is an easy measurement to acquire, measuring from the center of the BB to the top of the saddle.

If you want to make it more accurate then you can mask off your saddle and mark a line where the saddle is 80mm wide and use this as your reference point for getting your current setup and also replicating it on other bikes and with other saddles.

If you have your own method for measuring seat height, then you're already set. But if not, always taking the same reference point on the saddle, where it's 80mm wide, means you can then measure your height from there to the centre of the BB accurately and compare it to the geometry figures for certain bikes, or even replicate the same setup on other bikes with other saddles.

Once you know your seat height, and which size of frame you’ll be on, you can compare your seat height to that of the one stated for that size. If your seat height is higher than the one quoted then your virtual seat tube angle will be a little slacker. If your seat height is lower, then your virtual seat tube angle will be a little steeper.

If a brand is giving you all the information about offset, angles and seat heights then you can be sure that they are also designing their bikes carefully enough to have the seat in the center of the rails at the quoted measurements. This then enables you to fine tune your fit in either direction, not being backed into a corner with your adjustment. Moving your seat as little as 10mm can have the effect of over half a degree in virtual seat tube angle.



How does each measurement affect your saddle position?

Virtual seat tube angle – Simple. A slacker virtual seat tube angle puts your seat further back and a steeper one puts your saddle further forwards.

Actual seat tube angle – With all other dimensions held the same, a slacker actual seat tube angle will mean that for the same seat height the virtual seat tube angle will also be slacker, putting your seat further back.

Offset – With all other dimensions held the same, more offset will result in a steeper virtual seat tube angle putting your seat further forwards and less offset will result in a slacker virtual seat tube angle.

Saddle height – With all other dimensions held the same, if your saddle height is more than the bike's design then your virtual seat tube angle will be slacker and your seat further back. Less than the bike's design and it will be steeper and your seat further forwards.



What else is impacted by measuring seat tube angles differently?

Another measurement that is then rendered a little useless is the effective top tube measurement. This is the horizontal distance between the top of the head tube and the virtual seat tube angle.

Once again, our seats aren’t at that height when we pedal, so this measurement isn’t representative of the real world and can lead to further confusion when looking at a bike’s geometry on paper or comparing bikes.

In the same way that measuring your seat tube angle level with the top of the head tube doesn't represent real life, so too is measuring the effective top tube from it. With the seat up at a real pedalling position it moves back and away from the on-paper measurement. It's also using the virtual seat tube angle measured level with the head tube, making it even less representative of real life.

If your seat is at the same height as your head tube, then you’re all good, and most downhill bikes aren’t that far off this. But the riding scenario for downhill bikes leaves no need to know or care about the effective top tube length - usually the seat position on a downhill bike is a function of clearances to the rest of the bike and the rider.

Top tubes are another topic for another day. But there also needs to be some thought into having a more meaningful measurement that better represents what we would feel on the bike. Some brands have already begun developing with the non-horizontal distance from the top center of the head tube to the stated seat height to give a more realistic measurement.



Food for thought…

Our current system of measuring seat position used to be fine before we really started to mess around with the seat tube position. But in today's world it leaves a lot to be desired. Luckily a few brands have already started a movement to give more information to accurately show where your seat will be, and that matches up far closer to reality than what we are working with now. Fingers crossed that this catches on with more brands.

As a rider and consumer, the concept of seat heights, angles and offsets isn’t super hard to grasp. And armed with your own seat height information you can then get a better idea of how you would fit on a certain bike, or extrapolate from the information given from a brand to your unique case.

If nothing else, understand that seat height affects your virtual seat tube angle and knowing at the bare minimum these two measurements is a much better way to go for brands to communicate geometry and us to understand it.

Having an industry wide set of seat heights for the various size frames would make everyone’s lives a lot easier. But getting the industry to talk, let alone agree on anything is nigh on impossible.



Hopefully this edition of Enginerding has helped shed some light on the seat tube angle conundrum. Let us know what else you'd like us to go in depth with for more Enginerding articles.




173 Comments

  • 42 1
 I think it would be better to look at it another way. When we are looking at and considering seat angles, what are we trying to learn?
We are basically trying to get an idea of where our weight will be whilst seated. This weight is in relation to the bottom bracket and rear axle. Slack angle (which ever way you measure it) means weight over rear axle and usually poorer climbing. Steep angle and your weight is more over BB and usually better for climbing.
How about displaying where your weight falls (vertically down from top centre of seat post) as a proportion of the chain stay? Give two measurements. One for post level with top of top tube as this is a constant. One for the saddle at given distance above, and make this size specific.
A made up example could be:
Level with head tube your weight is 12% of the CS length behind the BB.
At 120mm above head tube your weight is 18% of the CS length behind the BB.
Each size frame uses a set height above head tube and make it industry standard. haha! Industry standards! haha.
100mm for small, 120mm for medium and 140mm for large frames?
This way you know how the position of the saddle, but more importantly you understand how this interacts with the rest of the frame design, most notably the CS.
OK....... I'm ready to be shot down by the engineers on here. Maybe I should stick to press ups!
  • 7 2
 This makes a lot of sense. When seated we want to know how "poppy" the front is going to be on steep climbs. This would give a meaningful figure for discussion where as STA and ESTA only really have meaning on paper. It would also take CS measurement out of the equation (although I think CS should be proportional to FC).
  • 5 1
 I'm on the same thinking as you, seat angle and virtual seat along with top tube just doesn't give the information you need to be able to judge if a bike is going to fit or not. If you take the reach and the top tube, subtract them from each other, you can get an idea of the bikes that might fit your pedaling position, but its by no means exact!

I'm going to call it seat offset: ep1.pinkbike.org/p4pb19134615/p4pb19134615.jpg
IMO, its way more accurate than the guessing game that is virtual seat angle and you know exactly where your seated position is in reference to the bottom bracket. @MTB-Strength-Factory yours is a slightly more complicated version, which the manufacturers are bound to implement in different ways to suit the marketing department.

There is some science behind steeper seat angles and the benefits: www.ncbi.nlm.nih.gov/pmc/articles/PMC5786204
  • 1 0
 While it's a good idea it's also a new idea and because of that no one knows what their numbers are or how a bike with a particular value would ride. So there would be a period of time where riders would have to guess and demo bikes to see what percentage suits their riding style.
With that being said I do like it because once you get that dialed in you can immediately have an idea of how a bike descends compared to yours (HT angle) and how it climbs by comparing your CS percentage along with the normal reach and wheelbase of course.
  • 1 0
 I think you are right that this is what we care about, the issue I have with this is the extra math would make it easier for brands to obscure what is going on. Honestly, it seems like brands should just have an interactive table where you input seat height and it spits out effective seat tube angle and the measurement you are suggesting here. It is simple trig if you have all the measurements and would be very easy to implement.
  • 3 0
 It still doesn't take into account the my seat is at X height. It would be closer, but still not the whole picture. Also Where you're weight is in relation to the bike isn't the only consideration, there is also how long the "effective reach" will be from seat to bars which can make a big difference. I think effective top tube tries to simulate this but has issues for the same reasons effective seat tube angle doesn't work.
  • 6 0
 I agree published metrics are more confusing than helpful and @dan-roberts is doing an excellent job explaining how so.

A weight bias approach as you propose is a step in the right direction IMO but it would still allow significant inaccuracies in the representation of the feel a rider would have climbing.

Let's take two setups with equal seated weight bias of say 50% on level ground and a small a 150mm difference (700 vs 850mm) in inseam length. As the climb becomes steeper, the weight distribution for the taller rider will shift back at a faster pace than the shorter one since the cg swings further up from the ground. For a 25 degree slope, the difference in weight bias can be more than 5-6% which is noticeable and only gets bigger as saddle height and slope increase.

That's why you need to make STA steeper for larger bike sizes if you want to provide a more consistent climbing experience, not slacker as pretty much everyone is doing. But doing so would mean larger reach and hence WB to account for the shrunk TT length. But we all ride around the same turns, there's no point in optimizing the bike around the rider alone without thinking of the trails... haha love these articles.
  • 4 3
 The other performance aspect of seattube angle beyond weight distribution is metabolic/physiological efficiency. Maybe your seat tube angle puts you in a great place for climbing in terms of weight distribution, but you've got a weird bend at your hips/back that makes your legs less efficient, or a posture that makes your breathing less efficient.

This is really into the weeds though and I doubt that many companies really look into BOTH the mechanical (bike) and the bio-mechanical (ride) optimization for deciding.
  • 9 4
 This is bullshit dude. Look at all the XC bikes with 73-74 Seat tubes. Seat tube angles have zero to do with how well or how poorly a bike climbs. It's all about the riders center of mass in relation to the wheelbase, not some value on a geometry chart.
  • 2 0
 You are correct, in that what constitutes "steep" or "slack" seat tube angles will depend on what your saddle height is! The industry is veering towards 76-78 degrees ESTA (measured at full saddle height) but that is really only valid for a particular size frame: Large. A rider on an XL frame (with a much higher saddle height) will be pushed farther rearward (relative to the BB or rear axle, whatever your frame of reference) and so will FEEL more slack. So a large size rider may feel 76 is perfect (and tell everyone on the forums that it is perfect) but 76 may be too slack for an XL size rider. And 76 ESTA may be too STEEP for a Small size rider, who finds their weight pushed too far forward and loses rear traction too easily. So, the modern internet geo chart (65/7Cool is really only valid for certain frame sizes (M to some extent, but mostly L).
Everyone with different saddle heights has their own internal definition of "steep" and "slack" and frame sizes need to start embracing different ESTAs for different size frames. Changing to a setback measurement (behind the BB, or as stated here, % of CS length) would go a long way to giving everyone (regardless of body size) similar experiences on the bike.
  • 5 0
 @MTB-Strength-Factory I like your different view on the topic. One thing that only looking at how our seated weight would fall in, or out, of the wheelbase would miss is the idea of rider fit between the saddle and bars, and also how that weight would be in relation to the front of the bike too, if you wanted to focus on where the weight falls.

I think the seat position idea is a balance of the two ideas of rider fit on the bike and how the weight is distributed between the two contact patches. The latter being a bit more involved to explain with the inclusion of terrain, suspension and bike setup. Describing the rider fit seems to be a bit easier, and a good rider fit generally leads to the weight then distributed in a good way between the wheels.
  • 2 0
 @sir-hc:offset will give much better understanding comparing to the angle, while it could be easily calculated, as a consumer the less math you do the happy you are
  • 2 0
 So we just need to look at it from another angle.
  • 1 0
 Why not present a virtual seat tube angle range (VSTAR)? Assume only the unweighted frame orientation, and list the VSTAR range from a point 200mm above the top of the head tube (slackest) to the traditional top of head tube point (steepest). If a rider was riding a slammed bar, he'd be at the steeper angle, since the top of the handlebars would be about the same height as the top of the head tube, and a typical rider that has a seat 150 mm above their stem/handlebars (assuming 50mm added stack) would be near the slackest angle. Any odd wheel combination or asymmetrical shock set up is the rider's choice and shouldn't be on the manufacturer.
  • 3 1
 While I think the numbers, however you would like to measure them, can be a useful guideline and rule of thumb, ultimately, you just have to sit on the bike and ride it and see if you like it.
  • 2 0
 @TheR: That's harder to implement for mail-order companies.
  • 1 0
 @nickmalysh: I can measure the offset with a wall and a tape measure, rather than the current eyeballing and number fudging that goes on at the moment! Look we have a 77 degree virtual seat angle, yet the actual is 72, then you wonder what random height they have the seat at! @TransitionBikeCompany state the height at which the virtual is calculated, which is really good, so props to them.
  • 3 0
 @MaplePanda: Good point, but when it comes to direct-to-consumer brands, you're taking a risk on a number of factors beyond just seat tube angles. Will you like how it fits? Will you like how it feels/handles on the trail? Will the suspension be too stiff? Too sloppy? You just won't know any of that until you take a ride on it, regardless of how many measurements and angles you have as data on paper. You can make reasonable guesses and assumptions on all of it, but it's still risky -- you'll never know about any of it until you ride it. I'm not sure why the seat tube angle would be the breaking point in all this estimation/guess work when it comes to direct-to-consumer brands.
  • 1 0
 @TheR: Very true. It's important to have both numbers on paper and a real life experience with the bike.
  • 1 0
 @MaplePanda: All I can say is, my current bike is direct to consumer, and while it is a a very good bike, it’s not the one I would have chosen if I had tried it and a few others out first. And it wasn’t any particular measurement that threw me off, it’s just the overall feel of the bike, which other might really like. Direct to consumer is just not for me, but if it works for others, it’s a good deal.
  • 1 0
 @TheR: Yup, that's just one of the risks you have to take when buying a DTC bike. Hopefully you can sell it for a reasonable loss and get another one you like better.
  • 1 0
 @MaplePanda: Given the covid situation majority of bikes became direct to consumer
  • 1 0
 @TheR: I got downvoted in the Lux thread for pointing out that buying a bike that invests heavily in racing and development will generally get your a better bike, but that didn't go over well. My next road bike will be a DTC I'm sure, so no hate for them.
  • 1 0
 @nickmalysh: I was talking more about the usual practice, before covid. Perhaps more brands will switch over to DTC during the pandemic while they have the opportunity to?
  • 1 0
 @MaplePanda: i do understand, however even with local bikeshops you suppose to travel 50 miles for demo nice bikes, rather then test co-op/whatever brands - dtc are more favorable option;

I do favor few brands just cause of easy access to test ride bikes, S since they almost everywhere and Intense since they local
  • 30 1
 It would be cool if companies had interactive frame geometry sections where you could type in your bottom bracket to saddle rail height and it would give you numbers for effective seat tube angle, effective top tube length, etc. There could also be graphs showing a plot of these measurements versus bottom bracket to saddle rail height.
  • 3 0
 I suggested this elsewhere in the thread before seeing your comment and agree 100%. It would be remarkable simple to implement and I think would be bring another level of understanding to the consumer.

I get why brands would want a simple single number to compare but it is really how all these things interact that determines how the bike will feel so a more interactive option would be great. With direct to consumer brands becoming more popular it seems like this would be more important since you often can't demo those bikes.
  • 3 0
 @mtmc99: The difficulty with this for a lot of these companies is that they're enormous corporations, so getting everything correct and on-time is shockingly difficult (trust me, I work with one). Now for smaller, streamlined companies? This would be a nice feature to add, and possibly feasible. Though likely not worth the cost because it might convert like 15 sales a year total.
  • 1 0
 @slimjimihendrix: Even then, I worry about each company doing this separately and the comparability of that data. Maybe this is something a third party should undertake. Yes, yes, that might work. A third party with the respect and trust of the MTB community. And ideally, a company that already has their hands on the bikes we need this info on. Or better even, a company that has a technology/process for carefully evaluating the geometry of bikes. Idk though I'm not thinking of anyone.
  • 22 0
 I just came for the... illustrations
  • 1 0
 yep me too!
  • 4 0
 Agree - I like how Taj's drawings look elementary (grid in the background isn't square, wheels aren't round) but perfectly capture the point.
  • 1 0
 Yep me too
  • 4 0
 @clink83: oooh, I like this thread! thanks!
  • 1 0
 @Tajlucas: Keep up the good work! I like your illustrations, it just feels like innocent fun on bikes as a kid.
  • 19 10
 I matters because why else would you buy new bike every year if not for major improvement like degree here and there, few millimeters difference in offset, hub spacing, reach not to mention revolution like adding an extra cog to a cassette or using a different brand of oil and seals in suspension. Wow that's really a game changer!
  • 80 1
 ...bikes are like compounding interest. It's a bunch of annoyingly slow changes, but then all of a sudden you look back and are blown away at how much better they are than ten years ago.
  • 9 1
 @brianpark: Good call.. and we also need things to complain about on the internet
  • 18 16
 @brianpark: That's true, but as the time goes by the changes start to matter less because the technology matures and so does geometry.
It wouldn't be an issue if the sites like this one weren't industry peddlers and exaggerated the benefits of certain geometry changes. Likewise, all new stuff seems to be great and flaws are only mentioned when there's a new replacement released.

There's no ideal tried and true mtb geometry like you have on the road because the terrain isn't pure tarmac and some ride big mountains with steep gradients and others ride undulating terrain.
  • 6 0
 @brianpark: someone should do one of those poll things with up to 4 choices each for the greatest improvements in the last 10 years. Mine would probably be:

Dropper
1xDrivetrain
Tire design
Pressure relief Saddle shaping

It's a tough call though, there's a few others vying for a spot because you're right, most of these changes (with some notable exceptions) happen gradually and add up to massive improvements over time.
  • 15 0
 @landscapeben: Easy. Ride the same bike for 5 years and only buy a new one then.

Then you've got a proper sum of improvements.
  • 3 0
 @brianpark: I'm on an old 26" FS and rode a friend's modern 29er Fuel Ex. It feels so much different! Not sure I like it though, but I'd get used to it.
  • 9 3
 @msusic: I'm so sorry this is happening to you. I recommend going out and enjoying your bike instead of reading articles discussing standards if they upset you.
  • 6 1
 Bikes have improved massively in the last 6-7 years, I cant see any major changes happening anytime soon, aside from gearboxes catching on (fingers crossed). You reach a point where things start to work as they should. Look at mx bikes, they havnt changed much in the last 20 or so years.
  • 3 2
 @msusic: truer words were never spoken.
  • 2 0
 @brianpark: 5 years are enough.
I'm quite happy with my 2016 specy enduro 29 but,out of curiosity, i've just rented a 2020 mondraker crafty.
Yes, one is a moped and the other not, but geometry improvements were quite notable.
  • 3 0
 @brianpark: I would say bike prices are like compounding interest. A bunch of annoyingly small increases, but then all of the sudden you look up and and are blown away at how much they now cost!

That said, the new bikes are far superior to those of even a few years ago based on my experience. The question is, what is compounding faster.... performance or pricing?
  • 1 0
 @msusic: not only that, they force you to come here and read it! Dastardly tactics, indeed.
  • 7 0
 @MTB-RVA: I don't agree. There's plenty to complain about in the bike industry, but $3K buys you a way better bike in 2020 than it did in 2010.
  • 1 0
 @brianpark: I could totally buy and ride/race a 2010 road bike and be happy with it...but I dunno many 2010 mountain bikes I would want to ride.
  • 1 0
 @brianpark: I know. I was saying it partially in jest and noted "new bikes are far superior to those even a few years ago". Obviously the top of the line models are silly expensive for the average non-racing rider. I say, if you can afford and want a $12K bike then spend away! And I do agree that $3K buys a lot of bike these days.
  • 2 0
 @landscapeben:

Improvements:

1. Bike Geometry/Fit/Frame design/Suspension. Longer top tube/reach numbers with wider bars and shorter stems leading to more capable/versatile bikes with less travel. Also, the industry has seemed to settle on the underlying engineering to make bikes actually work and be durable (looking at you AMP Research & ProFlex).

2. Droppers. The prolonging of the ability to continue to ride the terrain you like to ride as you age.

3. Wheel design. Wider rims, Wider tires, hub engagement, proliferation of carbon hoops. Ride wheels from the 90's and early 2000's...gigantic improvement.

4. 1x drivetrains. simplicity. weight. setup.


Unfortunately there is some collateral damage from all these. Bottom bracket standards, hub spacing standards, frames with geometries that are "out-of-date" after 2 years.
  • 2 0
 @landscapeben: 4 greatest improvements in mountain bikes in the last 10 years? Easy:

1.Geometry
2.Geometry
3.Geometry
4.Geometry
  • 3 0
 @brianpark: it does, mainly because of improved geometry. But I personally also believe the gap between production costs and MSRP has increased a lot. In absolute terms you get a better bike for your money now. In relative terms, what once bought you high-end now buys you low mid-range. 3K bikes used to come with full XT or X9 to X0. They now come with NX...
  • 2 0
 @landscapeben:
Geometry
Suspension design
Forks/shocks
Tires
Droppers

Would be my top 5. I'd rather ride a bike with those changes and the rest of the stuff from 10 years ago (spacings/standards/1X/wheels size, etc.)
  • 2 0
 @brianpark: I'd venture to say that If a pro were to race their setup from 5 years ago compared to their setup today, that there wouldn't be a significantly large time differential. 10 years ago, yes, 5 years not so much...
  • 9 1
 Being 6'4" (193cm), ive always struggled to get a bike to "fit". weight pushing further backwards than it should at the saddle making climbing a pig (thats my excuse and im sticking to it), but also the manufacturers rarely make, any significant increase in headtube length. Back when i rode 26" bikes, i just got used to sitting on top of the bike, ready to get ejected out the front door if the front wheel hooked up. My Giant Trance (a proper 105mm one, not a new fangled 120 or 140mm one), the headtube on that was like a keel/bow, but it still wasnt all that long. I think i was on the maximum of the steerer tube that came on my Revelations.

Now ive gone to 29er, and sitting behind the bars is a fantastic improvement. Who do i sue for all the years ive spent on an XXL bike designed by and for someone who was 5ft nuffin?
  • 2 1
 Same boat as you, 6’3” and can’t believe how much better a 29er feels. Wasted decades riding around on garden gates.
  • 2 0
 Ditto. 6'3" and just got a Guerrilla Gravity Shred Dig that I set up as a mullet. It's so great to feel like I'm finally "In" the bike instead of perched on top!
  • 1 0
 Same height, but I’ve got short legs. Now that seat tubes are getting shorter I can actually pedal a XL or even some XXL bikes and get the wheelbase I’m looking for!
  • 5 0
 This. I am also 6'4" and bikes being designed around 5'8-5'10"are just not optimal. Taking this back to the XC/DC comparo...it's one of the reasons why I am looking at bikes like the Spur, even though I'm looking for a XC/XCM bike.

First, there's no point in looking at the EVO as it would just become uncomfortable for me (as there's no XXL). Second, while everyone notes that XC bikes are long and stretched...being 6'4" with long arms and legs, I will still have a good bit of drop, but not so much as to be ridiculous. Finally, I have about 35# on Levy. While a 23# (if they made an XXL...I'm calling it 23#) would be nice, I don't know how much that 2-3# matters as much when you weigh 195-200.

People bemoan the tall stack (LaDuke) and I get it. Some people bemoan the steep STA b/c their wrists. But when your setup looks something like that giraffe's, the "new" geo is a game changer...or I'm just justifying getting a Spur. Smile
  • 2 0
 @smartyiak: Spur is definitely on the short list...
  • 2 0
 6'5 here. I've found finding a bike that fits over the years so frustrating. As seat angles have gotten steeper (which is good for us tall people), reach numbers and top tubes haven't grown proportionally. Steeper seat angles bring your body closer to your handlebars and the bike will feel cramped or you'll have too much downward pressure on your hands while pedaling. Yes, every bike is getting a bit longer each generation. But only by 10-15mm per size. If a new bike has a seat tube angle that is 2 degrees steeper than the previous model, I think it needs to be accompanied by a reach/top tube increase for 15-20mm per degree. So we're talking 30-40mm longer than the last bike. Otherwise the bike might feel the same size or even smaller than the last version. Hence why I'm seeing dudes who are 5'10 riding the same XL or XXL bike that I ride. Those are for us!
  • 1 0
 I'm 6'5" when I have good posture. I'm really loving my Pole Evolink because it actually fits me and is comfortable. The steeper seat tube angle, the 29" wheels, the long reach. It can be tough finding a good fit frame for us tall guys.
  • 1 0
 @smartyiak: you could just see a bike fitter instead of buying a spur. I have zero problems getting fit on an any XC bikes, and we're the same height.
  • 1 0
 @clink83: I can "make" a variety of bikes fit...but why not start with something already close to ideal rather than searching for band-aid solutions?
  • 3 0
 @smartyiak: Because if you buy a bike with a super steep STA that you intend to race XC on you are making yourself slow for no reason. Putting yourself in an upright position in front of the pedal spindle makes less power and puts more stress on your knees than a a properly fitted XC bike. The only thing that has limited my race bikes is the lack of range on 11 speed 1x drivetrains, not the geometry.
  • 1 1
 @clink83: So...I should avoid the new Epic?
  • 1 0
 @smartyiak: It has a 74 and change STA, that's not unreasonable geometry at all. Its when you get to 75 and up that you see people with saddles slammed all the way back to get the right fit. If you want to run a dropper getting the right STA is kind of important.
  • 1 0
 I would like to know from all of you tall guys what you're riding and feel like fits. Even better if the bike is from a more mainstream manufacturer, or something that's "affordable" which to me is about CAD $4,000 in total.

I too have and continue to struggle to find bikes that fit me, and I'm just 6'3" (but with very long legs and arms). Same argument: too short of seat tube and too short of head tube. Reach has sure improved though, but it's not everything.

Trek Fuel EX in XXL comes to mind. Anything else?
  • 1 0
 @rossluzz: I bought a Nicolai frame this year and it's comically huge, but it fits so much better. Other brands are catching up but really only a few options for us monsters.
  • 1 0
 @clink83: Speshy says it's 75.5.
  • 1 0
 @gdharries: The most comfortable bike that I've tried (as far as geo) was the 2018-20 Smuggler.
  • 2 0
 @smartyiak: I looked at the wrong geo chartSmile If you look closely the bike comes with an offset seatpost, so if you buy that bike you are getting a real world STA of 74 if you use their offset seatpost. If you have long legs for your height that might cause fit issues if you cant find a 25mm offset dropper. I have short legs for being 6'4 so 74-75 works fine.

If you look at the Oiz and Mondraker athletes most of them have the saddles slammed as far back as they can go to overcome the steep STA.

I would avoid the Epic just because of the Brain suspension, that alone is worth avoiding that bike IMO.
  • 1 0
 @clink83: I definitely agree with you on avoiding the Brain.
  • 1 0
 If you look at the Oiz and the Epic they both have 75 degree STAs in the 100mm bikes and 74mm in the 120mm bikes, too me it looks like they made a cost saving decision to sacrifice the geometry of the 100mm bikes because they expect to sell more of the longer travel versions.
  • 1 0
 @gdharries: For affordable but still up to date geometry check Commencal is probably your best bet. If you can squeeze a bit more from the bank Transition, Banshee and Knolly all do really well for tall riders without getting to exotic dollars (note Knolly tends to have pretty short stack heights though).
  • 1 0
 @gdharries: I'm ridding a 2019 Specialized epic hard tail and a 2019 specialized Stumpjumper 150/140 travel. Both bikes are XL frames, and I run an 84-85 cm seat height. These and my previous 2017 XL stump jumper fit me really well. I'm running 780 mm bars and OEM stem. The seat tube on the stumpy is short but I could easily run a 200 mm dropper. Even the epic with a 520 mm seat tube I run a 125 mm dropper and have a lot of post showing.
  • 1 0
 @rossluzz: 6'4 and been loving my evolink, finally a bile that actually fits me and i can climb the very steep stuff on without falling backwards, it just feels right
  • 1 0
 @gdharries: I'm also 6'3 with long legs and loooonnnggggg arms. I test rode an XXL hightower and was comfortable. My torso isn't super long and I am pretty happy on my XL Sentinel with the seat slammed forward and tipped forward (to straighten my hips). I do like my bikes with a shorter ETT and longer reach and the sentinel is a pretty playful size for me.

Personally I don't think I would get the fuel EX because I would have a oneup 210mm exactly bottomed out on a frame with a 540mm ST.
  • 1 0
 @CobyCobie: Interesting perspective. Why do you push your saddle forward on the Transition?
  • 1 0
 @gdharries: Awkward torso/arm ratio. It puts me in a nice upright position without being too stretched out.

I used to ride bikes with much longer ETTs but it sounds like you might have a shorter torso like me and personally I've found that I like a shorter ETT but long legs and arms dictate that I'm a bit cramped with a shorter reach.
  • 8 0
 At Ibis we took data from our demo drivers and complied saddle heights for each size frame that people test rode. We used the average saddle height for each size frame to design the geometries. Measured from the BB axle to the top of the saddle, saddle height by size is S = 650mm, M = 700mm, L = 755mm, XL = 810mm. When you see the seat tube angle on our geo charts these are the saddle heights for those angles.
One important thing to mention: if you have a very high or low saddle height for a given frame size (everyone is usually within 50-60mm of the average, according to our data), the ESTA does not change very much! A rider with a high saddle height on a large frame (could maybe ride an XL frame) will have an ESTA only 0.2 degrees different from the average rider's ESTA. So on a size L Mojo 4 (ESTA for average saddle height of 755mm = 76.6 degrees) the entire range of riders will have ESTAs +/- 0.2 degrees (76.4 degrees for saddle height of 815mm, 76.8 degrees for saddle height of 710mm).
My point is: ESTA, when measured at a realistic saddle height (not the top of the HT) varies very little with saddle height and you can rest assured that you are getting the geo as designed.
  • 3 0
 @AJMIAC nice information to know!
  • 1 0
 @AJMIAC good to know. Do you put that number on your charts in the website?
  • 1 0
 @bikedrd: The website shows this data only for the Mojo HD5 and the Ripmo AF. It's missing on the other bikes. I'll work on getting that info up for all the bikes
  • 7 0
 I simply don't think that (within reason) STA is going to make much difference, so long as your ideal pedaling position is within the degrees of freedom allowed for by saddle position on the rails. Ultimately, the angle that matters is where your hips are positioned, relative to the bottom bracket. How this is decided is dictated by your individual dimensions. Regardless of bike, ideal pedaling position is going to be a function of: 1. Crank Arm Length, Femur Length, Tibia Length, Foot Size + Cleat/Pedal Position.

When I read reviewers saying "I wish the STA was steeper.", I have to assume that they are saying this because they already have their saddle slammed as far forward as possible. More often than not, this is reported from people who are trying to upsize to a bike with longer reach (example: someone who is 5'10", trying to ride a bike with 490mm reach numbers).

So long as your frame design and saddle rail lengths allow you to move your final seated position to optimize how your legs apply pedal throughout the power stroke, there is really nothing else to fix. This is why seat tube angles in road biking are stuck at 73-74 degrees (+/- depending on sizes) for race bikes. There is no more innovation to be had once the pedal position is optimized to your body - and pedaling positions and fit are fairly well vetted and decided upon at this point in cycling.
  • 6 0
 Sag Matters. A 76deg seat tube angle on a 170mm enduro bike will not be the same as a 120mm down country bike with the same 76deg STA once your weight is on the bike. Things get even worse once you actually start going uphill and weight shifts rearward even more.
  • 5 0
 I would like to see a behind the numbers type article on the difference between unsagged and sagged bike fit on long travel bikes.
  • 3 0
 @mikelevy @brianpark Do it for the page views!
  • 2 0
 I heard it from a professional shock tuner, the sag of a shock should be around 25%, front and rear. Since the critical shock performance is when the bike is going downhill, and setting the bike on an actual slope is not always easy, the usual recommendation is around 30% rear, 10% front on a flat surface. The front and rear sag are going to be different when pointing uphill and it should be considered when examining the bike geometry, including seat angle, leverage ratio, anti-squat, etc.
  • 2 0
 @theboaz: That's not true for all bikes though. The Orbea Oiz is designed to have the rear sag set at 15%. In general that is correct though.
  • 2 1
 I think if you're already considering dynamic bike geometry and that we ride up hills then you've got a good understanding of the topic!
  • 1 0
 @clink83: yes - this is the point I was trying to make, many times we get information that is over simplified, to create a one-size-fits-all numbers, while some of the parameters that are left out, actually make a big difference.
  • 4 0
 As long as you have enough adjustment fore and aft between the seatpost head and rails, STA doesn’t matter that much. Reach is what determines how a bike fits, and that’s an easy thing to measure. 2 bikes with different effective seat tube angles but the same reach will fit the same if the seat on both bikes can be adjusted to the same position relative to the bottom bracket.
  • 1 0
 You're both clearly shorter guys.
  • 2 0
 @CONomad: Tall guy here, I agree with him.
  • 3 0
 The good old seat angles topic, so many variables that nothing really works.

Vital is great but it doesnt consider the influence of suspension on the seat angle, you would have to provide a whole table of sag v inside leg length. but at the power position of a stroke the crank arm length and foot position comes in to play too for the "real angle".

Probably better to just leave it at 2 sizes, neither of which are any good with modern bikes and leave the punter quoting numbers like stack and reach of every bike even though setup plays such a big roll in both too.

I even remember running a layback post backwards way back in the day to steepen the seat angle of a bike, the clamp only just worked to get saddle angle, but it steepened my VPfree for XC days as I only had 1 bike to ride everything and only changed a few bits between rides. (wheels, shock, post)
  • 3 0
 I think manufacturers should just list the effective angle at different inseam lengths. That could either be by frame size along with the average inseam the frame size is designed for or simply a chart that lists inseam lengths and the corresponding effective STA.
  • 2 0
 Transition does this and I think it’s pretty reasonable. Having effective and actual STAs will allow people to sort the rest out for themselves.
  • 3 0
 I believe Norco and Forbidden do this as well. But basically nobody else. If a company doesn't vary chainstay length and seat tube angle by size you know those bikes are going to suck for anyone not in the middle of the bell curve. It's that simple. With carbon bikes getting individual moulds for front triangles and rear ends cable of having flip chips to vary length it means those companies just don't care.
  • 1 0
 @alexsin: Santa Cruz lists STA by size but don't list what inseam they're basing that off of.
  • 4 0
 Keep it simple. If you can climb comfortably or better, praise the seat angle. Else, blame the seat angle. Never ever doubt your fitness or the donuts you had last night.
  • 2 0
 @DanRoberts How about "Butt to Bar". Measurement from seat (on centre of seat post) to centre of bars at your pedalling seat height. It would need to be quoted for various seat heights.

I used this when I got my new FS frame to compare to my HT frame. Despite a 75mm difference in reach the butt to bar is within 10mm. FS bike as progressive geo, HT is a little dated but has a comfortable pedalling position. The upside was the CS were within 1mm of each other so I knew the new bike would go up hill better as it has a steep ESTA.

Also larger bikes need to have steeper ESTA and longer CS to keep the F/R balance the same and keep the seated weigh in the same location relative to the centre of the rear wheel as a smaller bike. Taj's drawing showing the different bike sizes shows this really well.

All that said there is nothing quite like demo-ing the bike you are looking to buy to get a proper feel.
  • 10 8
 Seat tube angle is an unimportant number for me. And it should be for any rider.
As long as I can get my saddle in the correct position in relation to your BB I don't care where my seatpost is. Than the angle of the tube only affects where my seat will end up in the low position (or mid). If it's going to be a bit further forwards or backwards when you lower the seatpost. Personally I don't care where it ends up (down). If it's 10mm for or aft. For adjusting the top possition of your saddle - if your seat rails don't have enough length for your ideal fit, there are different offset seatposts.

The only real benefit I can see it that steeper STAs put less pressure on the telescopic seatpost internals.

What should be more discussed is ideal bike fit and especialy ideal bike fit for MTBs where you spend much more time in steep climbs than on the road which is the basis of bike fitting. And steep climbs completly change your bike geometry in terms of fit.
  • 3 1
 Came here to type this but you beat me to it Smile
When I look at bike GEO for fit, I look at reach and stack and figure out what post offset/height and stem length I like based on my current rig.
The STA just tells me if I need an offset post or not. Maybe it’s important because 90% bikes come with Fox Transfer which doesn’t offer an offset (why I sold mine and picked up a 9.Cool .
  • 15 3
 Do you realize that seat tube angle defines the relationship between your seat and bb? It’s the only angle that matters in determining the one thing you say you care about.
  • 3 1
 I have a trek slash (should be enough info for you right there lol) and the main thing I am cursing about it is the seat tube angle. Even with the seat slammed forward I still can't get to the proper position. Such is the problem when you have proportionally long legs and a 64 degree actual seat tube angle. SO I disagree, there are many problems with some bikes that require a steeper seat tube angle. What companies are finding is that the steeper sta puts the rider in a better position to find the proper fit.
  • 3 1
 @powderturns: Nope, there are two numbers that define the relationship between the seat and the bb (3 if you include seat offset). 1) STA and 2) BB offset from seattube. Look at the image were the "offset" os depicted in orange. In theory, you can enlarge the offset and slacken the STA as much as you want (for a given seat height). This is the equation that must be maintained: "saddle height"/sin("ASTA")="offset"/sin("VSTA"-"ASTA"). just FYI. So it will not change the seat position. So if you had two bikes set up like this (different STA same saddle possition), without telescoping your seatpost up and down or actually looking, YOU WILL NEVER BE ABLE TO TELL THE DIFFERENCE.

Thats why STAs on their own are not impotant. OK...if you have weired fit, STA might give you some idea if the bike is going to work for you in saddle hights the frame was not designed for. I suppose that's less than 10% of riders.

...And thats also why we should be thinking more about climbing fit vs level fit and not a few degrees of STA here and there. A few companies have been trying to address thiss. For instance the Shapeshifter bike, or Specialized with the tilting telescopic seatpost. And also all the travel adjustable forks.
  • 3 0
 This. Thank you. So tired of the "steep seat tubes climb well" nonsense.
  • 4 0
 @powderturns: It's pretty obvious that he is saying he doesn't care "within reason". Obviously we care if the bike has a 60 degree angle, or a 90 degree angle. But assuming the bike is somewhere in the realm of modern 73-77 degrees, you can probably adjust your saddle on the rails to achieve what matters: ideal position of hips to BB.
  • 1 1
 @clink83: Exacly. What the "steep seat tubes climb well" crowd might be actually thinking is: "I like to climb with my seat in a very forward possition and descend with my seat as far back as possible" (I am not aginst it, but frickin someone should say it LOUD) ...but it seem they can't verbalise this line of thought Big Grin
  • 2 0
 @powderturns: If you install your saddle in the exact same position on an identical seatpost, then yes STA will absolutely determine the only thing I care about. But because I buy offset seatposts and position the saddle position relative to the BB, I can get there on any bike with any STA by adjusting the fore/aft position.
  • 1 0
 What we need are dropper posts with a FORWARD offset head.
  • 2 0
 As a bit below average height guy with only a 165mm dropper seat tube angle seems overblown. Not only that but you have the rails on the saddle to make a up for a degree or two. Plus I like being an inch or two further back from optimal in my seated position. Most the time I am climbing it is not super hard tech moves. When I need to tech move a hard climbing bit my core tightens up and I move forward on the saddle an inch or two to the optimal position. When back an inch or two and cruising I never feel like the front end wants to lift up and I have a little more forgiveness if I get lazy and roll a small root seated. But I do see how it would be different for the Daddy Long Legs of the world.
  • 5 3
 "On a suspension bike the seat tube angle gets slacker as you go through the bike's travel."

What? Does this "suspension bike" not have a fork? On my bike, 150F/144R, the seat tube angle (actual and effective [virtual is not the right word]) is within a tenth of a degree at full (fork and shock) squish. On bikes with an even more pronounced "reverse mullet" (longer in front) travel numbers (we've seen bikes with around 20mm difference), the seat tube may actually get steeper at full squish.
  • 3 0
 I'm pretty sure this is in reference to seated climbing rather than soaking up an impact. As you climb and more weight is shifted to the rear shock it compresses more while the fork decompresses and raises both combine making your STA even slacker, something a hardtail doesn't deal with.
  • 2 0
 I have never really believed this claim either. If you have a LLS bike if your bike sags so far into the travel that you go from a 78 STA to a 74 degree like everyone claims you would be way over the rear end and your bike would lift the front end on the climbs.
  • 2 0
 @CONomad: Then the author needs to specify. The sentence about the hardtail says "fork goes through its travel", but no mention of climbing. So why would someone assume the next sentence (the one in question) is about climbing, and not just the bike going through its travel in general?
  • 2 0
 @clink83: I tend to agree. Yes, going up an incline with shift weight (relatively) backwards, thus sagging the rear of a full-sus more, but the rider has to make a weight shift forward (dropping shoulder/chest, sliding forward on seat), even on a hardtail, to keep from unweighting the front too much.

One could even argue that the sag is beneficial in that the center of gravity of the bike/rider system gets lowered, thus negating some of the rearward weight shift.

Obviously some frame & rider combos will end up with a really slack effective STA, enough that the needed chest drop will become "too much", and that sucks. But for most people, anything modernish (mid seventies effective) is a pretty good compromise between helpful on climbs and still comfortable on even terrain (where many people dislike having the pedals so far under their hips. There is a reason only TT riders use TT positioning: it sucks to pedal like that unless you're trying for max aero and/or using different muscles than running)
  • 2 0
 I got an Idea, and bike companies can have this one for free for the common good. Lets keep theoretical seat angle the same across all sizes. Just use the room gained in making the chainstays on larger bikes longer to reduce seatpost offset and make the actual SA steeper as bikes go up in size. Thereby adjusting for higher seats.
  • 2 0
 Maybe I spent too much time in the fitting room, but I end up setting my saddle fore/aft in relation to the crank (for pedaling efficiency and to avoid knee injury) regardless of STA. If I had a bike with a really steep STA, I would end up buying a rear-offset dropper and slamming the rails back. Opposite for a slack STA. Only time I look at the number is when I calculate what would be needed with a new frame to get the saddle in my known comfortable position.
As far as balance point and getting weight shifted around, chainstay and wheelbase will determine that if I position my saddle in relation to the BB.
  • 3 0
 But how will the designers and brands hide the fact their seat angles are slacker than an 80s road bike if they have to give us the offset and saddle height?
  • 1 0
 As long as you have enough adjustment fore and aft between the seatpost head and rails, STA doesn’t matter that much. Reach is what determines how a bike fits, and that’s an easy thing to measure. 2 bikes with different effective seat tube angles but the same reach will fit the same if the seat on both bikes can be adjusted to the same position relative to the cranks.

That said, I do prefer the more forward position of modern bikes, however you choose to measure it.
  • 1 0
 I got curious about the trig to calculate using actual sta, offset and seat height.

Definitely an ugly formula, but a pretty simple spreadsheet. Publishing for anyone who wants to use it:
docs.google.com/spreadsheets/d/1X0nk1vcS2gd268cD4K4GGA4Nf5GDsQ9hLhSex1beN-k/edit?usp=sharing
  • 1 0
 ESTA, or "Effective Seat Tube Angle," has become a marketing term devoid of any physical meaning on a bike.
What we need are ETT - Effective Top Tube, and the actual seat tube angle (you'll probably have to go to your LBS and put your angle-finding smartphone app against the post to figure this out because most manufacturers won't list it for fear of getting called out on their BS "ESTA" numbers.) Once you know the actual angle and the ETT, you can get a pretty good feel for how it's going to feel under your butt. You can also get a good laugh at just how BS those ESTA numbers are - 10 degrees or more isn't uncommon.
If you prefer a low-tech approach to this, grab a string and some kind of small weight and drop a plumb-bob off the nose of the saddle on a bike that pedals well. You'll probably find that the string/weight falls 30-80mm behind the center of the bottom bracket. Much more than that and it won't pedal up steeps very nicely.
  • 1 0
 This is interesting on a few levels. I've just bought a 2020 Whyte T130, now I assumed the seat angle would be steeper than on my 2010 Marin Attack Trail, it turns out, however, that the Marins' is considerably steeper!
  • 3 3
 @dan-roberts
While we're at it, shouldn't we also talk about how reach is measured from the top of the headtube, but does not take into account the length of the headtube.

So a bike that has a reach of say 450mm and a head tube of 130mm at 65 deg HA is actually longer than a bike with a 460mm reach and a head tube of 100mm (all else equal).

And don't get me started on the whole short stem and riserbars issue... Wink
  • 1 0
 That's true but (how I understand at least) reach should be used to have an idea of the rider position, with this in mind it's logic to have the top of the head tube. If you want informations about bike length you usually have the wheelbase in the geo chart
  • 4 0
 @kosumo: Yes and no Wink
Assuming you want to have the same stack height on both bikes you would need to add 30mm of spacers on the bike with the shorter headtube, which in turn makes for a shorter reach for the same possition of the stem in relation to the frontwheel Smile
  • 2 0
 @kosumo: Reach is standing only. Butt to Bar is seated.
  • 1 0
 @eldsvada there are a few flaws in your comment. The only place you really can measure reach is from the top of the top tube. The stack height will take in to account the head tube length so the head tube length is really irrelevant.

Also do you mean that a bike with a 100 mm head tube has a 30mm lower stack than one with a 130mm stack.
If this is the case the bike with the lower stack will feel like a way longer bike as the bars are further away from your shoulders.

In your example above the bike with 450 reach and 130 head tube (with all else equal) will be longer from BB to top of top tube but top tube will be shorter to shoulder so the bike with 460 reach and 100 head tube will feel a lot longer.
  • 2 1
 @MTBgeometryguru:
In my example I'm comparing two otherwise similar bikes. If I was considering both bikes one would have to assume that I want the same stack height regardless of which bike I'm buying.
Therefore the stack height including spacers will be the same for both bikes once the 30mm spacer is added to the bike with the shorter head tube.

The logical thing in order to have a measurement that can translate between bikes would be to measure reach and stack at the position of the crown race of the fork Smile

(BTW, did you down vote my comment because you didn't agree? ????)
  • 2 0
 @eldsvada: Ok so in that scenario with a 65 degree head angle the bike with 30mm of spacers will now have 12mm less reach than it had before so it has now gone from 460 to 448mm. It is now 2mm shorter than the bike with the 30mm higher stack height in your scenario above. In that case, Yes you are right. I just didn't pick up what you're putting down.

It is not logical to measure stack height to the crown race as that is not where your handle bars are bolted on unless you're one of those gravel bike riders. If you used this scenario you would then need to add the length of the head tube and take in to account the head angle to try and work out where your bars are going to be in relation to everything else.

No I didn't down vote you. Not my thing!
  • 1 0
 @MTBgeometryguru:
I'm glad we agree on the mathematics Smile

When it comes to the stack height I think the same goes there, it more comparable between bikes if it's in relation to the fork crown. But then again, for me the geochart is primarily to be able to compare geo between different bikes and not to translate it to a specific rider position. That's something I need to fine tune on the trail once the bike has been built up (-:
  • 2 0
 What I like about straight seat tubes is that when the seat goes down, it really goes out of the way. With these kinked tubes the seat comes forwards kissing your knees.
  • 3 1
 "Good God! I've been sayin' it. I've been sayin' it for ten damn years. Ain't I been sayin' it, Miguel? Yeah, I've been sayin' it." - Every person over 6'6".
  • 2 0
 A big thumbs up for this, and your beautiful Swarf which showed me that real bikes for doorway-duckers do exist!
  • 1 0
 This is why I bought and sold an evil within a week.... it couldn't climb hills in the Netherlands my ass was so far over the back wheel. Expensive lesson learned.
  • 1 1
 It is preferable if all bike manufacturers use the same standard to define seat tube angle described in the first half of this article than for each manufacturer using different assumptions for saddle heights. No change needed IMO.
  • 1 0
 If you want to see slack seat angles, just search for the Schwinn 4 Banger or Straight Six. I remember seeing them back in the day when riding and thinking WTF? Looked like the rider was seated over the rear wheel.
  • 1 1
 I hope my bitching about this contributed to the development of this article. No matter what each individual thinks how new methods of measuring contribute to ones decision about a given bikes fit we need more. That more would be better access to demo's. The demo events are nice but still lacking. If bike shops want to get a leg up on the direct to consumer brand hear is an idea for both the MFG and shop. Shops need to carry a full line of models and sizes. Yes a big challenge. The other is to allow say two to three bikes available under one demo charge. I don't need to ride a bike for a whole day to get an idea if i like it or not. I also don't want to pay three times to demo three bikes. If a shop is close to trails charge me $150.00US for a full day or two and let me take out three bikes. That maybe three different bike or maybe different sizes.
  • 1 0
 Hate to be that Ripmo fanboy but on the geometry chart they give you the saddle height at which the effective seat tube angle is measured at, which is super helpful considering we buy based on reach now.
  • 3 0
 Great illustrations, kept me reading.
  • 3 4
 virtual STA should just fade away, you add 10mm more headtube and leave rest of the things unchanged and suddenly your STA becomes slacker? all we need is the actual STA and offset, that's more than enough to judge how the bike's gonna feel like.
  • 1 0
 I love my seat tube angle and anyone, especially a PB reviewer, who says they found it rubbish doesn't know how to set it up.
  • 1 0
 This info is all well and good. But 85% of people still don't know what a properly fitting bike feels like or how to accomplish that.
  • 2 0
 Glad this is being addressed, thanks! Steeper seat tubes for L and bigger is good start.
  • 1 2
 "It’s an angle measured from horizontal to the line from the center of the bottom bracket up to the intersection of the actual seat tube angle and the top of the head tube."

Is it though? Have bike companies told you guys something we don't know? So far when we have asked "But what seat height is the effective STA measured at?", we've only gotten back a snarky "They didn't tell us so how could we tell you?"
  • 1 0
 3 actual seat tube angles at 3 distances from bb Fully slammed, middle and seatpost at heighest. For universal application just say 18,22,26 Simple
  • 2 0
 I don't have enough money to worry about seat angles but I csn make my legs and arms stronger for free!
  • 1 0
 Ok, but it isn’t involved trigonometry, just use the law of sines:
STA(eff) = STA(act) + arcsin(Offset * sin(STA(act)) / Seat Height)
  • 1 0
 Many athletes wish they could get bikes that actually fit them as well... like Emily Batty.
  • 1 0
 This is really well done! More about geometry, fit, and similar subjects, please.
  • 1 0
 If steep seat angles are supposedly better for climbing, then why do most hardcore XC bikes have slacker STA's?
  • 1 3
 Slacker STAs are more aero, assuming one can tolerate the acute hip/torso angle. They can also accomodate a taller rider without having to increase mainframe length, which would mean more weight. Also, it's traditional.

If a triathlete designed a full-sus XC frame, would it be proportioned more like e.g.Turbo Kenevo, but with 80mm of travel and a somewhat steeper HTA? Someone's going to have to prove it with race results. There'd be less crashing. 'Safety' may be the truest of Pole's marketing claims.

I don't know if Schurter could jump so well from lower speeds on progressive geometry, as sudden uncrouching/unfolding is important for active jumping.
  • 1 0
 @ceecee: Lack of travel and much higher compression ratios keeps the rear end from wallowing, same reason hardtails get away with it.
  • 1 0
 @Tajlucas does the zipper graph in the chalkboard signify how horny you are for knowledge?
  • 3 0
 zipper tires sales graph!
  • 1 0
 @Geochemistry: don't even need to see the measurement, I can tell from the photo that the STA is way too slack! Nice compact wheelbase for jibbing though...
  • 1 0
 After the reading... I am listening Iron Maiden- Virtual XI
  • 1 0
 Hahahaha, that was a good one Smile
I am listening to Led Zepp - Dazed and confused
  • 1 0
 Looking forward to have a virtual head tube angle!
  • 1 0
 Just call them steep tubes Smile
  • 1 0
 Wow, I thought I knew, but I had no idea. Great article!
  • 1 0
 companies already do this.
  • 1 0
 I just like Taj's illustrations !
  • 1 0
 At 6'2" how do I wear a medium shirt and a ride a XL bike?
  • 1 0
 Try before you buy.
  • 1 0
 Exactly, bikes with identical numbers still can feel way different from each other.
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