Video: The Basics of Modern Mountain Bike Geometry - The Explainer

May 6, 2020 at 10:01
by Mike Levy  


THE EXPLAINER

The Basics of Modern Mountain Bike Geometry



You've probably heard it said before: Geometry is the single most important factor in determining how your mountain bike will perform. It's not the only piece of the puzzle, of course, as your tired, over-worked suspension and worn-out tires also count for a lot, but it's geometry that takes the biggest slice of the what-matters-on-your-mountain-bike pie chart. Let me put it to you this way: Adding the latest Kashima-coated, 17-way adjustable suspension to your 2005 Big Bouncer won't do much beyond giving you more dials to turn before you bounce over the handlebar. But give that 'ol rig geo from 2020 and it'll instantly be easier to ride and far more capable, stock suspension notwithstanding.

Geometry has changed a lot over the last decade; numbers that used to make complete sense now seem downright scary, and terms that used to be important are less so. There were smart folks building bikes like this long before the bigger brands caught on, but it's only been in the last few years that forward-thinking geo has been (almost) universally embraced. It's probably time to have another look at modern mountain bike geometry, and while you can make it as complicated and interconnected as you want, that's not the gist of this Explainer video. Instead, we'll go over what the terms mean, what they do on the trail, and how they've evolved since that '05 Big Bouncer.



Previous Explainer episodes:
Episode #1 - What's the Deal with Linkage Forks?
Episode #2 - Carbon Fiber Leaf Springs
Episode #3 - What's the Deal with Chains?
Episode #4 - What's the Deal with Cross-Country Racing?

Author Info:
mikelevy avatar

Member since Oct 18, 2005
2,032 articles
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160 Comments
  • 128 0
 Levy has the audacity to eat a donut whilst not releasing the only video that we actually want ....smh
  • 93 2
 Trolling not so softly... Smile
  • 8 0
 Shouldn't be surprising, I'm pretty sure Levy survives solely on doughnuts and energy drinks
  • 3 1
 I think Mike Levy is an anagram for Homer Simpson, Grim Donut, or "I Meekly."
  • 7 0
 @mikelevy: "No bike has perfect geometry"


ENTER GRIM D.
  • 7 0
 @mikelevy: The "Reno sucks" on the whiteboard is some next level trolling.
  • 2 0
 @mikelevy: Heres a question for you;

I thought that contact (trail) was actually that. So, the question is how does the amount of slack change any amount of trail a bike has regardless of the specific tire size (i.e. a 27.5 will always be the same and so on)? From my limited understanding of circles and piviots the "trail" shouldn't ever change (minus a few mm's due to tire pressure. Right? Or am I totally off here? Or does this relate how much downward pressure a bike applies to the earth...?
  • 2 0
 @Agolz12: I'm pretty sure Mike ain't so highfalutin. He eats donuts, not doughnuts.
  • 2 0
 At 1:01 there is actually a shot of him riding the Grim Donut
  • 71 0
 I've experimented with anglesets for my bottom bracket, but time after time I find myself coming back to the 'ole traditional 90* sideways.
  • 19 0
 Depends on the track i reckon. If you have more left hand corners, a few degrees left can help
  • 14 0
 I had a similar experience experimenting with anglesets for hubs.
  • 6 0
 To be honest I didn't really notice any difference running the 80 degree BB. Maybe it is all marketing.
  • 3 0
 Kinda depends on which side you're packing on, if you know what I mean. Getting that BB angle wrong can result in some serious chafing due to improper leg angles.
  • 49 0
 Wrong. Clearly my bike has the perfect geometry. I know because it was expensive and convincing myself it is perfect allows me to justify the cost of buying it.
  • 6 0
 Now you must tell everyone else your bike is the best/most superior in every way and they need to buy one too
  • 1 0
 It is painful how true this is.
  • 8 0
 Clearly my alloy bike is the best, because I can’t afford a carbon one. I tell everyone that carbon isn’t worth it and you can get an alloy bike with perfect geo. At least until I can afford a carbon bike.
  • 2 0
 That's also why expensive bike owners get so offended by people complaining about mtb prices. Bc they need to justify taking out a mortgage on their house to buy one!
  • 35 0
 It’s all about the angle of the dangle
  • 16 0
 ? I thought it was the rise in your Levis?
  • 10 0
 You just need to know that it's inversely proportionate to the heat of the beat.
  • 1 0
 Comm guy...
  • 26 0
 Bound to trigger at least 1-2 "experts" from the forums. - love to see that.
  • 29 0
 Expert here, someone rang...?
  • 35 0
 "Background - I'm an engineer"
  • 15 6
 @jpat22: lmao, I actually am, sounded too cliche to say though haha!
  • 46 0
 Surprised that angry Swedish guy hasn't shown up yet.
  • 48 18
 During my lifetime career as an expert and riding many bikes with different geometries I came to a conclusion that experts are worth crap. What you need is someone who has a nice cabin, can carry a tube for you, roll joints, grow mushrooms, keep beer cold, invite ladies, and keep away creepy ass middle aged dudes.
  • 6 1
 @h20-50: yet you've managed!
  • 4 1
 @subwaypanda: Ha! The only I managed as an engineer is learning to keep boobs, beer, and bikes to a minimum for 4 years so I could study in the nerdery!
  • 55 1
 @WAKIdesigns: You are a creepy middle aged dude.
  • 11 7
 @hamncheez: got me a mermaid!
  • 9 0
 @WAKIdesigns: You need someone to keep you away?
  • 1 0
 @WAKIdesigns: I can support that ... so I'm assuming you are that guy Wink
  • 9 0
 Im a creepy middle aged dude and an engineer. I fricking own this thread.
  • 2 1
 @WAKIdesigns: I'm glad you didn't say 'creepy ass old dudes'.
  • 1 0
 You called?
  • 2 0
 @nurseben: I suck at everything in the list so at least I am trying to learn to grow mushrooms...
  • 2 0
 @WAKIdesigns: When life gives you lemons, you make lemonade. When life gives you shit, you grow mushrooms.
  • 2 0
 @just6979: the best bit about mushrooms is that they give you motivation to get out of the shit, since having them while in to will just push you deeper
  • 24 2
 Just give us the grim donut goddammit
  • 21 1
 The what now? We're filming some more for it this week, but the 'rona really slowed it down Smile
  • 17 0
 @mikelevy: maybe you should stop drinking then.
  • 6 0
 @mikelevy: So you’re saying it doesn’t handle difficult situations well, not supple off the top of a pandemic, got ya
  • 7 0
 Chill peeps, the slack bike is slacking. What did you expect? If you want sharp, nimble and quick, bugger off to Cyclingtips. They've recently reviewed the Caring Carrot, well before the bike was actually designed and built.
  • 23 2
 I miss the old days when you bought a bike just because it looked awesome.
  • 22 0
 still can but science now.
  • 7 0
 Bonus: You get plenty of time while recovering on the couch to look at it looking awesome when you crash horribly because it's a shit design...

Klein Mantra being _the_ prime example.
  • 5 0
 @just6979: Wow, the Klein Mantra is still catching flack in 2020! Big Grin
  • 5 1
 YES!! in the early 2000's Everyone's bike was their own science experiment......metal, punk rock and endless shuttles. Then someone let all the nerds in........
  • 2 0
 @just6979: "The Mantra is engineered for extremely technical off road riding, where large obstacles and steep descents are likely to be encountered." MTBR review of the '99 Mantra

Just thought I'd leave that there.
  • 1 1
 they started making ugly frames to fit bottle mounts in
  • 1 0
 @SoddenDeath: Engineered does not always mean engineered correctly.
  • 1 0
 I buy (or avoid buying) bikes based purely on color.
  • 1 0
 @HouseofDaedalus: of course. Blue is worth 0.27 seconds, or 2.7 watts, depending on your preference
  • 15 1
 Shoutout to Meeshka for holding the measuring stick at the end of the video.
  • 11 1
 So.... I need a ride with a slack front bottom, and a long extension. Got it.
  • 11 0
 "Allow myself to introduce....myself" Big Grin
  • 3 0
 @bman33: dude, that is my favourite Austin Powers quote! haha what a great line.
  • 6 2
 Knowing your bike is far more important than someone telling you what geometry you need. We are all different ,trails are all different. I'll stick to top tube length , stay length and HT angle . For quick reference. Then I ride the bike. There is no substitute for experience.
  • 6 1
 Add reach to the list, maybe even move top-tube to the bottom (because it can be tweaked by sliding the saddle). Unless you never descend out of the saddle...
  • 3 2
 @just6979: for me reach isn't top on the list. I spend most of my ride seated (up takes longer than Down) so top tube is more important. I think ppl are pushing reach based fit on a lot of ppl who don't need it. I think many riders probably value over all comfort over straight line speed capability. Seat tube angle is also up there, but not just to allow reach. We've got rolling trails as well as winch and fall, so I find any steeper than 76 degrees too much and less than 74 too little.

My Geo appraisal is hta, sta, ett, wheelbase, then cs and reach.
  • 4 1
 Reach, HTA, BB drop, CS length, in that order.
  • 1 0
 Seat angle isn't important to you? Makes a huge difference for big climbing days. That's high on my criteria for my trail bike.
  • 4 0
 @gtill9000: reach without stack height doesn't mean much.
  • 1 0
 @mgrantorser: HTA alone isn't worth much, wheelbase needs to be taken into account with it. For STA are you talking actual or effective, and how do you know the effective is valid for your seat height? Ff course ETT is important for seated pedaling, but it's got some adjustment with the saddle rails. And without taking CS into account, ETT alone isn't really a great indication of climbing feel. Reach isn't just about descending either: having more room to move around while staying within the "breaking rear wheel traction vs looping out" window can really help with steep and/or technical climbs. I suppose if you're doing hill-climbs, ETT, or actually saddle to bars, and "saddle over BB" become important more important. But having the forgiveness/larger-sweet-spot in descending positioning built-in with a reasonable reach seems to make sense if you ever have to go downhill.

And since reach does not totally limit saddle-to-bars (can be tweaked with saddle position and stem height and length), it's silly to place it so low on the list. At that point it's not swapping descending for climbing, it's just taking away descending flexibility for zero or very little uphill gain, since the climbing trade-offs can more easily be offset compared to the descending trade-offs
  • 1 0
 @kanasasa: But effective stack (frame stack plus spacers, stem, bars) can be changed more easily and directly than reach.
  • 5 1
 Effective STA isn't very helpful when you have no idea what height they measure at (I think I've seen 2 manufacturers specify it, 1 at multiple heights). That 74° effective STA might not sound horrible until you realize it's measured ~4" lower than the height you set your saddle at AND the actual STA is ~64° (I'm looking at you, Trek). We all love sitting closer to the rear axle than the BB, right?

Hopefully we'll stop seeing so many kinked seat tubes now that seat angles are steeper (more tire clearance) and dropper posts are getting longer.
  • 1 0
 100% - came here to say this, he touched on the effective vs actual, but effective needs seat height factored in or it's worthless.
  • 1 0
 Chain stays are also returning to proper lengths, so that helps
  • 1 0
 @zyoungson: amen to that. Being 6'2" (1.88m) I can't wait to get back to 440+mm chainstays.
  • 3 0
 bit misleading on front-rear center. Most people and manufacturers consider it a horizontal line from the axle to BB, not from the axle directly. Then it would vary based on BB height. Chainstay length seems to no be standardized, however, and some manufacturers measure from the rear axle to the BB, while others just the horizontal distance, making it the same as the rear-center.
  • 6 0
 It would be nice if all manufacturers just said both. Of course it won't happen, just like we won't know seat tube angle at different heights or seat tube offset, but it's nice to dream.
  • 3 0
 I’m currently faced with the decision of whether to upgrade or replace my nomad 3...friends claim newer geo trends climb better and descend as well...has there really been that much change since ~2015?
www.santacruzbicycles.com/en-US/bike/nomad/3

I do like my nomad, and I ride it so much I’d have a really hard time comparing it to any demo fleet bike that doesn’t have my suspension, tires, brakes etc...like most of us I’m particular what I’m used to.

Maybe there isn’t an answer to this, but if anyone has thoughts about maybe what weaknesses they see in that generation’s geo compared to the even more modern trend I’d appreciate it. It definitely seems to have a slacker STA than what I see nowadays (visually...I probably should start comparing the actual numbers lol). Is that all it takes to make a bike a better pedaler?

That said, based on the vid it sounds like geo is all over the place with different brands, so maybe not a comparison that’s easy to make?

It’s funny to have taken a sport so seriously but feel clueless with stuff like this. I used to struggle dialing in my suspension back in the day, but at least with that you can hunker down and start testing on the trails etc...I just don’t know how to learn what I could / would prefer from a geo shift when I can’t get a frame up demo for several days with all my same components and setup that I currently have.
  • 2 0
 Dang brah... how do you even ride that thing if you're not pushing 64 or slacker up front or 77 or steeper out back?

Not to mention it's a couple inches too short (twss!).
  • 4 1
 Try a bike with a steeper seat-tube (really it's longer "effective chainstays" when seated that you want: seat further forward relative to the rear-wheel), and see if it feels nicer when climbing. May be able to achieve the same thing by slamming the seat forward on the rails or going to less offset on the seatpost (if you still have one with offset).

Then try a bike with a longer reach (will likely have a longer front-center, too, which is really the key) and see if it's nicer to descend. Only way to know for sure. Also important is "out-front" (front center minus reach-plus), which is how far the front axle is in front of your hands. More out-front is generally more forgiving to potential OTB events.

Be aware it can take some getting used to because it will be more work to weight the front wheel, but the margin of error between too far forward (leading to OTB) and too far back (leading to unweighted front and washing out) is _much_ bigger on a longer (reach and front-center) bike, which means you can drive the front wheel into corners hard enough to get some sweet drifting or berm shredding with much less fear of going over the bars, which is just awesome.
  • 1 0
 Similar situation, I'm still riding my first gen nomad c I bought almost 10 years ago. I think something people forget or don't understand is what it's like to ride literally nothing but the same bike for 10 years straight. It starts to feel like an extension of your body.
  • 2 0
 I've recently come off a Nomad 3 to a new Hightower and it's quite a difference. The Hightower is just as capable as the Nomad in the steeps, but more playful. With longer reach you're more centered on the bike so there's better traction and the longer wheelbase helps in the steeps. The improved front end grip provides better cornering and the big wheels hold an offcamber line much better. The only negative I'd say is the steep seat angle feels a bit weird riding on the flat to the trail head, but I'm not bothered by that. To be fair, I loved the Nomad too though.
  • 4 0
 So why upgrade anything?

What year is your car/truck? How about your household applicance?

So some things may matter less than others, a good set of tires and a suspension rebuild might suit a person just fine, but then at a certain point old is old, so it just depends on what you want from your stuff.

In theory, with the exception of a few outliers, bike geometry has steadily changed over time for the better, so the older your existing bike, the further you are from the current standards.

To each their own, but I figure two to three years as a "flip" point, but some folks might go five years, after that you either don't care that much, can't afford to care that much, or you just don't know any better.

If you ride a lot and you're replacing suspension, drivetrain, wheels, etc... then a new bike makes more sense.
  • 4 0
 @just6979: "out front" doesn't have anything to do with the end angle, whatever the "out front" is.
  • 3 0
 Definitely a case of can't afford to care that much.
  • 2 0
 youtu.be/P18SutYYL5I
  • 1 0
 @clink83: end angle?
  • 4 0
 @nurseben: well my predicament lies in that I wasn’t quite ready to pull the trigger on a new build, and most of my drivetrain was way overdue for replacement, so I went ahead and got a new cassette/chainring/mech pulleys/chain.

Pistons were shot in one of my zees so I just swapped to a saint out of necessity.

I’m tired of the lack of adjustability on my lyric, but it feels questionable whether I should swap a 36/38 on there or just rebuild my lyric and deal with it until I’m ready for a frame up.

I’ve historically swapped AM bikes every 5yrs or less as I hadn’t found one I really liked the fit on, and the nomad has been my favorite so far.

I’m rambling, but I guess I just have this feeling that it’s so soon to already be building a new bike when I like the one I have. Plus it’s hard to be excited about cutting a huge check for a new frame
Up when I could just get a new fork and maybe be happy for another 3-5yrs.
  • 5 0
 Push the seat all the way forward and you will see the difference of a steeper STA. The Nomad 3 is light AF compared to newer bikes. Its still a relevant bike. Hopefully yours came with a 36 or lyrik vs pike or 34.
  • 1 0
 @nvranka: if the lyrik is the most bothering thing on there, try a new damper. You should be able to drop in a Charger 2.1 RC2 or RCT3, and get all or most of the adjustments. Shit, you might be able to get a Push HC97 on there. And it's not an adjustable thing, but maybe even try either of the DebonAir spring updates to see how they feel.
  • 5 0
 @nvranka: Honestly the only real big difference in geometry is that they made the reach 2 cm longer than your current bike. I'm actually shocked to see the Nomad V4 didn't get the same steeper seat angle that the bronson V3 did. So the new Nomad will feel 2cm longer both seated and standing.

Unless your bike feels too small in both positions there is absolutely no reason to upgrade. The fact that the new Nomad didn't get a steeper seat tube angle with its longer reach means it might actually be worse.
  • 4 0
 @just6979: I don't think long chainstays help quite as much as a steeper effective seat angle. I've ridden bikes with fairly long chainstays (~440mm) and the steeper seat angle still helps quite a bit. When the trail gets really steep and you have to put a lot of power down to keep the bike moving forward, a slacker seat angle makes me feel like I'm pushing myself off the back of the bike with each pedal stroke since the pedals are farther in front of me. The long chainstays help a bit, but I still have to pull on the bars and lean forward to keep my weight centered. Slamming the saddle forward feels like it allows me to put more power down while keeping my upper body more relaxed, since the pedals are a little farther back below me where I can push down on them instead of forward.
  • 1 0
 As an XC guy, the move away from 70°+ HTAs has been a godsend, and made a huge difference in my riding. Maybe it doesn't matter as much if you're on older trail bike geometry, which was still way better than older XC geometry.

While I think the long, low, slack thing has generally been great, it's quite possible that the industry will overcorrect. They've gotten geometry wrong before! Like Gary Fisher's old G2 which cut the trail way down and gave you a bike that was twitchy as hell. I guess the Scalpel is still doing that.

www.youtube.com/watch?v=PwR0T5a4uuM
  • 2 0
 thanks for the input guys, lots to consider

also, fyi when i said upgrade I should have specified that I would not upgrade to the v4 nomad...would probably look at a slightly overforked 130-150mm rear travel bike of some kind....that's a whole other can of worms...

ripmo / hightower / sb130 lunch ride....and I'm sure 10+ other solid choices.
  • 2 4
 I'm probably gonna get a lot of downvotes and hate... but I tell all my friends who have solid bikes (ie. Nomad 3) to get an ebike with modern aggressive geo instead of buying another acoustic bike. A 2 bike quiver of your Nomad 3 with a modern aggressive geo ebike is in my opinion perfect. The Nomad 3 probably isn't holding you back too much on anything and if you get a modern agressive geo ebike, you can hit the same things as your Nomad and experience modern geo. The ebike will allow you to do recovery days that are 2 to 3 times longer than your acoustic ride in almost the same amount of time and 100% fun up and down.
  • 1 0
 @GBeard: yes I remember. Been on my 'new' bike for nearly 6yrs now. It is good to ride.
  • 1 2
 @nvranka:

I am riding a very similar bike to yours ( HD3) my advice is if you like it keep riding it. I have tried newer versions of bikes and found that there are trade offs more so than “upgrades”.
Longer, lower, slacker, means harder to ride thru tight and twisty single track. more reach, wheel base and slacker head angle means the bike won’t turn with leaning it over , and the front wheel will slide right out if you don’t really put weight on the front of the bike. The steeper seat angle is great fro places where you ride straight up and straight down, but not so much for flat to rolling terrain.

Are the new bikes better, maybe? Are new bikes really expensive, yes.
  • 3 1
 @caldog: I don't think you'll get any downvotes for suggesting an ebike as there's nothing wrong with that (except it's completely off-topic and not what the OP is asking about). You'll get them for using the absolutely idiotic term 'acoustic bike' for what is actually called a 'bike'. Stop trying to pretend you need any qualifier for people to know what a bicycle is, as if that was something new and needed a fresh definition. Ebikes are the relatively new thing that needs the 'e', 'electric', 'pedal-assist' etc. qualifiers to define them. If it does make you feel better though, at least use something accurate like 'non-electric'... I mean, I hope you do realise what the word 'acoustic' means and how it is not applicable to bikes in any way, shape or form?
  • 1 0
 @just6979: endo. Sorry my phones autocorrect sucks.
  • 1 1
 @nattyd: I'm still riding a 70 degree HTA bike. HTA has very little to do with anything other than steering feel. It's vastly overrated.
  • 2 1
 @bananowy: I don´t think you are aware of acoustic bike being widely accepted term for unassisted bikes.
  • 2 1
 @Mondbiker:

“You keep using that word. I do not think it means what you think it means.”
  • 1 1
 @WasatchEnduro: I´ve never used that weird term before personally, but it´s pretty normal on this forum and maybe even was created by one of the PB editors and the banana guy acts like the guy made that one up himself. Well, no, he is using what someone else thought fitting and obviously necessary to describe a bike. Just like they deemed necessary to come up with downcountry and others.
  • 2 0
 @Mondbiker: I love how you assume that if someone disagrees with you it must be because of ignorance and not because they, well, disagree. Nice one pal.

I'm perfectly aware of some people using that dumb term, though luckily that use is nowhere near being 'widely accepted' at least from what I've seen (YMMV). Even here it's quite rare and coming from a minority of commenters rather than editors (and invariably called out as asinine). Where exactly is it more common, the German "Bike Magazin"? That would be fitting. I think I recall someone pushing it hard under an article on NSMB and it wasn't very well received.

And where, oh where did I ever suggest caldog made the term up? You're the only one making things that I didn't say up, buddy.

Question though. Even if the term one day becomes adopted like downcountry, will it make it any less stupid? Or any less of a silly make-believe that ebikes are the norm and bikes are the oddity (which might as well be the case in some years but that's off topic)?

Hugs, "the banana guy"
  • 1 1
 @bananowy: I get that you don't like the word, I think it's dumb too, but to say he has no idea what a word means when he's quoting an editor from this website....maybe you need a new website.
  • 1 0
 @bananowy: I believe it was first time used in article on this very site...I don´t read german mags in general and especially not if it´s about ebikes, lol. I´m not a fan of the term either so I don´t know why do you think I disagree with you, what I´m saying the guy you were answering didn´t come up with it he used what is commonly used here, if you want to blame anyone blame Levy or whoever created it? I just ride my bike and I think you know what that means, no extra word needed to describe it.
  • 2 0
 @friendlyfoe: another projection, I never said he had no idea what the word meant.

Why would I 'need a new website'? Because someone on this one said something I didn't like? Now that would be weird if you ask me but hey, I won't judge if that's how you roll. Besides, where would I go, Bikeradar? I'd rather call bikes 'acoustic'.
  • 1 0
 @bananowy: "I mean, I hope you do realise what the word 'acoustic' means and how it is not applicable to bikes in any way, shape or form" - Bananowy

Same thing
  • 1 0
 @friendlyfoe: No, it's the opposite thing. I very specifically suggested he knows what it means, you just quoted it. What I don't know is why I'm even getting dragged into a pointless argument about this.
  • 1 0
 @Mondbiker: All cool, 'disagree' was probably a poor choice of word on my part. But yeah, I was aware he didn't make the term up and didn't need that explained (though still wouldn't say it's super popular either). I don't know why it irritates me tbh. I don't mind downcountry and other newspeak like that at all but when I see 'acoustic bikes' I lose my shit for some reason Wink
  • 1 0
 @bananowy: I would say it´ more popular than it should be (it should be illegal).
  • 1 0
 @clink83: I think steering trail is more important than HTA, but since trail is largely a function of headtube angle (obviously fork offset, fork length, tire/wheel size as well), it changes steering feel a lot, which matters a lot! And, to call it "feel" is selling it short. It reduces the mechanical instability of your steering when you hit an obstacle, which momentarily means that the contact patch is ahead of the steering axis and your trail is effectively negative, i.e. that your handlebars want to flip 180°.

Slacker HTA also puts your center of gravity further behind the front wheel, making the bike less prone to endo.

There are a lot of great mountain bikers who could kick my ass on a 70°+ HTA bike, so it's not all that matters. But as far as geometry goes, it matters a lot!
  • 2 0
 I think front/rear ratio is something that should be taken into consideration. I have noticed that despite front and rear centers getting longer, most bikes still maintain a 65/35 front to rear ration as it relates to the total wheelbase. Would a 60/40 front to rear ratio be better?
  • 2 1
 It absolutely would be. Not varying rear center to match front center is a design compromise to save money. Most XL bikes are way worse than they could be. FC RC ratio is usually the first thing I look at on a geo chart. But people riding smaller sizes probably don't have any issue with average geo.
  • 1 0
 Most bikes only have that ratio for a given size (probably L or M). Smaller frames get closer to 60/40, and larger frames get closer to 70/30. This is stupid, because that ratio does have a lot of influence on the handling of the bike. Many short people might feel like a given frame in XS is easy to turn but hard to lift the front wheel (because relatively long chainstays) where a tall person on the same frame in XL might be manualling all day but turning becomes a chore because the relatively short chainstay throw off the front-rear balance.

The answer to your question is "depends on riding style/goals". The 60/40 might feel great for a racer who wants that front-rear balance for railing messy corners, but the jibber might want that 70/30 to keep the back wheel tucked in for manual-ability and flick-ability. Either way, it would be nice if riders up and down the size range would get the same feel for a given frame, and it is starting to become a thing (though the media's insistence that 29ers are the answer for everyone and everything doesn't help, because it's hard to get the chainstays short enough for good balance on an S or XS 29er).
  • 1 0
 @just6979: This!
A lot of road bikes adjust HTA and chainstays to make the whole range ride similiar, but its pretty rare in mountain bikes. I wish they would adjust geometry to give the same handing dynamics. XL bikes generally should have a slightly steeper HTA, and S/XS frames should have slacker ones.
  • 3 0
 There is a rapper named Offset?

Apparently I don't pay enough attention to musicians to understand basic culture references anymore.

Do I try to blame this on COVID19, or do I just accept my boring old guy card now?
  • 5 0
 RENO AS F*CK! Peavine, Tahoe, Lost Sierras, we got it all!
  • 6 5
 No mention of biometric effect of putting the seat closer to over the bb. It causes the quads to be worked more and the glutes to be worked less. Going up a steep incline this won't be the case as much, but on flatter terrain it will.
  • 6 0
 It could have been an hour-long video with there being so much to talk about.
  • 6 1
 Steep STA = increased hamstring and glutes activation.

www.ncbi.nlm.nih.gov/pmc/articles/PMC5786204
  • 4 0
 @dflano: Cool paper! I have a long-running argument about this with my wife, who once had a coach slam her saddle down and back because it improves "glute engagement". I've maintained that if a rearward seat position helps with power generation, it doesn't make sense that triathletes, time trialists, and track pursuiters all set records by going forward. Or that getting "on the rivet" is an age old way of squeezing out a little more power in a time of distress.

The paper only addresses 3 quad muscles and one hamstring muscle, however, and says nothing about glutes, except to note:

"only four muscles were investigated; whereas, cycling involves contribution from many other lower-limb muscles. It is recommended that future studies include other lower-limb muscles such as Gluteus Maximus, Semimembranosus, Semitendinosus, Tibialis Anterior and the Triceps Surae complex."

In summary, it actually says that going steeper improves quad effectiveness and increases hamstring activity, but it doesn't speak to glutes.
  • 3 0
 @dflano: I appreciate that you posted the study but it actually disn´t prove what you say it dis. It came to conclusion that steeper SA leads to more effective engagement of quads (vastus madialis/lateralis and rectus femoris are all different heads of quadriceps femoris) while the only hip/knee flexor (biceps femoris) they were measuring was less active with steeper SA. Glutes activity wasn´t even measured in the study, why would they not measure it is a mystery to me.
  • 1 0
 @Mondbiker: Probably because it's hard to stick an electrode to someone's butt?

It seems like they had a hard time measuring hamstrings as well, and ultimately weren't able to deduce a significant difference as a function of STA:

"A total of 5 out of 44 (11%) data sets were eliminated due to the appearance of non-physiological signals, with most being confined to BF recordings. Excessive motion artifact associated with electrodes and leads attached to the posterior portion of the leg during the pedal cycle most likely caused this. It may also explain the higher variance in BF activity patterns reported in previous studies"
  • 1 0
 @nattyd: sound pretty easy to me, certainly not any harder than sticking it to a quad lol. Or be a little more hardcore and use invasive monitoring.Maybe they were just too shy to ask.
  • 1 0
 @nattyd: TT/tri bikes sacrifice power for aero, so comparing their positions to normal bikes has zero relevance position wise.
  • 1 0
 @nattyd: Yeah pretty much.

They used surface EMG, meaning they can only measure muscle activity of superficial muscles. Quads and RF are easy to palpate and give very reliable signals. That would be my guess as to muscle choices. Science can sometimes be more about what you can measure and prove rather than what they think might be going on.
  • 2 0
 @clink83: That's not what the literature says. If you read the paper and its citations, they evidence says that steeper seat tube angle leads to less physical exertion for equivalent power, in addition to better aerodynamics.
  • 2 0
 Apart from several studies proving a steep STA is more efficient I have my personal experience comparing my old 72 deg XC bike with my 77 enduro. The difference is night and day, most prominent on tech climbs but even on flat terrain generating higher power on the XC bike requires standing up on the pedals. Slack STA are a relic from road bikes.
  • 1 0
 @clink83: they'll sacrifice upper body position and any power gain/loss from that for aero, but they're not giving up much/any aero by getting hips closer to directly above the BB.
  • 1 0
 @nattyd: I'm happy someone actually read the paper. My mistake. I should have read the full paper ha ha. Good on you for calling me out. The paper is actually very limited in scope so not the best. However as you said it does conclude that there was an increase in Quads and decrease on Biceps Femoris with steeper seat tube angle.

As we are nerding out, here's a much more comprehensive study. It's a bit older but gives us way more information.

open.uct.ac.za/bitstream/handle/11427/27901/thesis_hsf_2018_chye_teo_choon.pdf?sequence=1
  • 2 0
 Wheelbase is the sum of all other geometry factors becoming optimized. Steeper seat angle, slacker head angles, longer reach, shorter stems, longer chain stay. All contribute to longer WB. Embrace it.
  • 2 1
 Embrace it, until you roll up to a tight switchback.
  • 2 1
 @RonSauce: You can keep on embracing if you know how to corner in the first place.
  • 3 2
 @mikelevy Effective seat angle, perfect way of frigging the geometry chart. About time there was a better way, call it seat angle offset. Horizontal distance from the centre of the bb to the centre of the seat rain at a standardised saddle height based on the size. Oh and bike companies, go and check the meaning of standardise, don't go making a mess!!
  • 1 0
 I am driving my old motorhome quite a bit these days as my jeep's 2.4L is need of a rebuild (my mistake buying it I didn't know it was different than the underpowered but enduring 2.5L).
So I am getting real used to the long low stability focu
sed handling, I think I'd be confident at costco on xmas eve
Too bad my old Demo has such dated geometry I would probably be amazing with a modern bike.
  • 4 0
 "RENO SUCKS" - who's Reno?
  • 4 0
 F*ck that guy. Big Grin
  • 3 0
 Dunno, but I heard he sucks.
  • 2 0
 The Yeti bike realy brings out the color in Mike's eyes ... he's so dreamy Wink

So hey, donut guy, where's the Donut for the rest of us??
  • 4 1
 Meant to say geometry is second to tires
  • 2 0
 Fork offset! It works hand-in-hand with head tube angle in determining trail!
  • 3 0
 Levy's dog: This STA is pawfect!
  • 1 0
 And as bikes get longer, the wait for the Grim Donut review does too. Guess we will get the review, when 57° HA is state of the art.
  • 2 0
 Not bothered about Geo or numbers, all I know is my specialized enduro is limited by my lack of skills Smile
  • 2 0
 that orange Monster hits different
  • 2 0
 Especially the third one before 9am.
  • 1 0
 Reach extends by 20 mm, 50 mm stem feels too stretched, buy 30- 35 mm stem, ahh, that’s better.
  • 1 0
 And realize your 3 year old carbon wonderbike frame only isn’t worth $2600. Its rubbish b/c of obsolete geo
  • 2 0
 Big Bouncer review drops tomorrow. Figures...
  • 1 0
 White board has "Reno Sucks". Inside joke? Or are you truly not a fan of NV??
  • 2 0
 is his trail dog really his mechanic ?
  • 1 0
 Can’t find one of these new Nobikes anywhere online? I hear they’ve got the perfect geometry!
  • 1 0
 There's a rapper called Off Set? What does he do in his spare time...I'm a f*cking delight.
  • 1 0
 More thoughts on the effect of offsets in forks, with a side of donut.
  • 1 0
 Yo this video just cleared every single thing up...every. single. thing.
  • 1 0
 I did not know Costco on Christmas Eve was the place to be...
  • 2 1
 Geometry Tires
  • 4 4
 I wish manufacturers made flip-chips for STA.
  • 5 1
 Umm, slide your seat forward?
  • 1 0
 @nurseben: It is all the way forward. Im 6'6".
  • 2 1
 Reno Sucks Skid more.
  • 1 0
 Does it rally though?







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