# To the Point - Wheel Diameter VS Fork Offset

Dec 17, 2013
Fork offset is basically how far the front axle sits ahead of an imaginary line that runs through the steering axis. The most visible evidence of fork offset are the short extensions for the dropouts that house the front axle. Less obvious is that most fork makers also angle the crown slightly to provide part of the offset as well. When all bikes had 26-inch wheels and similar head angles, fork makers and frame designers settled upon 40-millimeters or thereabouts and that's where it remained - until the 29er appeared.

Gary Fisher liked 29ers, but hated the heaviness of the steering. The Fisher folk experimented with different offsets and discovered that 51 millimeters gave his 29ers a similar feel up front as a 26-inch bike. Fisher's 'G2 Geometry' was born and with it came more widespread knowledge of how the relationships between head angle, wheel size and offset play in the bike's steering equation. Today, there are a number of offset options available for production forks. RockShox, for example, offers 40, 42, 46 and 51 millimeter offsets.

In this chapter of 'To the Point,' Pinkbike attempts to clarify why fork offset changes with each wheel diameter and touch on how wheel size and head angle factor into the steering equation.

 DH forks appear to have minimal offset, but much of the distance is made up in the fork crowns. Offset crowns also give big bikes a slightly better turning radius.

What does fork offset do?

Fork offset is used to adjust the amount of 'trail' in the steering geometry. More offset equals less trail.

What is trail?

The distance that the center of the tire's contact patch falls behind the imaginary point that the steering axis (center of the fork's head tube) passes through the ground. This is what causes the bike's front wheel to self-straighten when it is moving forward. More trail firms up the steering and adds straight-line stability. Less lightens the steering pressure at the handlebar and gives the bike a more nimble feel. Too far in either direction makes the bike difficult to control.

How much trail is best?

The correct number varies with head angle and other factors, but somewhere between 80 and 90 millimeters seems to be the sweet spot that produces a light feeling at the handlebar, with a stable feel at speed, and with predictable cornering.

 By using more offset for the 29er fork, it can be designed to replicate the trail numbers of a 26-inch bike. The 27.5-inch size was excluded to more clearly illustrate the contrasts.

How does wheel diameter affect trail?

As wheel-diameter increases, the axle moves farther back along the steering axis, which increases trail. With a 68-degree head angle, the difference between a 26 and a 29-inch wheel is 15 millimeters (.61 inches).

How does the bike's head angle affect trail?

Trail increases as the head angle becomes slacker.

How is fork offset used to adjust the trail to the correct amount?

Adding more offset reduces trail by moving the center of the tire's contact patch forward, closer to the steering axis.

What is the relationship between fork offset and head angle?

If one of the offset options offered by the fork makers does not provide the frame designer with the desired amount of trail, he or she can change the head angle by a half degree or so to correct it. For instance: the slow steering of the 29er can be quickened by adding a slightly steeper head angle, then the designer can bring back some high-speed stability by choosing a fork with less offset to add some trail. The reverse is true for slack head angles, where the designer can erase some of the heavy wheel flop by adding offset and thus reduce the trail.

 Stepping up to a larger-diameter wheel without compensating for fork offset increases trail - which further slows the steering and imparts a heavier feel. Slacker head angles also boost trail and require more offset to compensate.

Wouldn't an adjustable offset feature be the best solution for fork makers?

Not in the real world. Experiments with various fork offsets show that getting it wrong is far worse than riding a bike that is nearly perfect. Now that fork makers are providing options, for the most part, bike makers are getting it right. That said, if you see CNC-machined fork crowns on World Cup DH bikes, or stanchions that are noticeably angled on single-crown forks at the EWS, they are almost certainly fitted to alter the fork offset.

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Member since Mar 23, 2011
974 articles

• 163 0
Ah, finally an unbiased To the Point, without anyone pushing their own products
• 60 6
• 8 4
Great information! Explains why some bikes I've ridden feel "twitchy" to me with the same head angles as others. Thanks PB!
• 11 2
@elanto not really, RockShox is mentioned, and not in a bad light either.
• 3 0
i wonder what those god-awful monoshocks have?
• 9 5
How could they not mention Suntour!!!! this is the most bias one sided artcicle ever!!!! (Pinkbike Sarcasm Alert)
• 5 8
@corywilliam The new Cannondale Lefty Max has 60mm of offset. I also assume that by "god-awful" you mean you've never ridden one? I've owned 2 for my single speed and all mountain rig a few seasons ago and it's the best suspension on the market for their intended use. And it's a strut, not a "monoshock."
• 5 0
He was referring to old forks that had the shock just under the steerer.....
• 30 2
i love articles about geometry, i'd love a bike that i could adjust all the aspects of geo on, so i could understand how more or less of everything affects ride properties... can't beleive the lax attitude and 'boring/yawn' type on comments, geometry is one of the fundamentals to a good bike, all the fancy materials and tech in the universe won't make up for sloppy ride characteristics. and knowing why you prefer bike X to Y...
• 4 1
You need one of these soon to be taking the MTB world by storm collaborations from a certain designer of bikes from Scandinavia (via Poland). waki-leaks.blogspot.se/2013/12/waki-leak-1-geo-djuster.html
• 2 0
I agree. This is awesome, and understanding the correlation between a bike that feels sloppy and loose and the amount of 'trail' the fork offset, wheel size and head angle all create. Bravo, PB. I learn something new everyday!
• 6 3
Aaaaaahhh sloppy and loose
• 28 1
its a conspiracy. They're trying to prepare us for 47" wheels.
• 2 1
• 1 0
The funniest thing about that 36" bike is that it has like a 12" seattube. Makes no sence at all and looks silly.
• 5 4
Kinda like a 29er lol
• 23 1
Anyone who owns a fixie with a flat bar can simulate the effect of a lot of trail by spinning the front wheel 180 degrees and then trying to ride it. It will want to always go straight and will fight with you to turn the thing. In fact, you can get off the bike on level pavement (say in a parking lot) and give the bike a shove and it will coast along upright on its own usually until it slows enough to simply fall over.
• 117 7
I read your comment and agree, people should get off their fixies and give the bike a good shove before letting go, preferably next to a large cliff or similar place.
• 13 57
Mattin (Dec 17, 2013 at 13:34) (Below Threshold)
@EuanBisser145: Please leave and go blow a bagpipe or something. There's no room for haters like you within cycling.
• 73 1
It was a mere joke but if you insist I'll go play my bagpipes and get my kilt on. Whilst I'm doing that could you please tell me how it is to live in a windmill and ride wearing clogs?
• 50 9
We sadly don't have those here anymore. I do work in a coffeeshop selling weed and all the girls I know are prostitutes.
• 21 2
I wish l knew some prostitutes.
• 7 1
• 3 2
My first comment was ment ironically too btw. That I call you a hater while being a hater myself in that same comment. Should have went for the words 'no place for discrimination here' to make it more clear.
• 3 0
Euan, i agree with you completely, but Mattin that comment about coffe shops and prostitues is literally the best thing ive read all week
• 15 0
increasing offset decreases stability? that just melted my brain. i always imagined a fork with the dropouts inline with the steering axis would be an unrideable twitchy bastard, yet the more i look at these pictures, the more i think i was wrong and you are spot on correct. but i still cant get my head round a fork with massive offset being less stable at high speed. Must drink tea now and sit down for a good think.....
• 6 0
its not that the bike is unstable... its that your hands have to work more, but not by much because of the massive leverage from the handlebars.
• 7 0
offset decreases trail which makes the bike more easily steered, or "twitchy" if its too much offset

this is a photo of motorpaced racing on the velodrome... these riders are commonly doing 45-50 mph average speed... the forks are so offset for stability that they look like they are mounted backwards... they dont like to turn, but the rider can go in the hurt locker pretty deep, have a lot of Gs pulling on him in the bankings and the bike is still stable...
• 5 0
The net effects on stability and speed of steering can only be properly assessed after both the steering angle and the fork offset are taken into account. It is the effect of steering angle and offset on (mechanical) trail that is the crucial point. Slackening the steering angle for the sake of stability at high speeds will tend to produce a heavier less responsive front end geometry at low speeds (due to the increased trail). But, it is possible to compensate for this unwanted steering sluggishness by increasing fork offset which will return the trail to a normal (i.e. sweet spot) value. By doing this steering responsiveness is restored and a general improvement in handling can be achieved.

If you wondering why steering angles don't get further slackened and trail further increased it is likely due to the fact that by doing so only small improvements can be gained. To a significant degree the impact of slackening the steering angle and increasing offset negate one another. The whole thing is a balancing act in which there are only small gains to be made. And as the steering gets slacker other problems like wheel flop become harder to manage. Still there are companies that do not appear to accept the current consensus on steering angles and fork offset. Marzocchi have always preferred a 44mm offset for their standard 26in forks (where the industry standard is 39mm more or less) making them suitable for bikes with slacker steering angles. And, Cannondale are now using a 60mm offset on their Lefty SuperMax 29er fork (a good bit greater than the common 51mm). These variations from the norm are not crazy, and may in the long term turn out to be the better geometry compromise.
• 4 0
@eriksaun. I want one of those wack-a-do stand-up motorcycles! Are those used for drafting?!
• 1 0
Yeah. Look them up. They are called Stayer bikes. On the road we used to pace behind a honda 125 with a roller on the back hacked on from a set of Kreitler rollers.
• 3 1
I think the simplest way to understand this concept is to look at how the front wheels (or all 4 cause europe is pimp that way) on a shopping cart move around when you push or pull it
• 1 0
Quick question, when it comes to the difference in offset for the same fork design, what componment is changed to give the different offset amounts? e.g. is it the upper crone of the fork or the lower legs?
• 1 0
it can be anywhere. usually the upper crown has some offset built in, and the dropouts add a little more. it seems these days when a fork is produced with different offset options the difference is made up in the dropouts.
• 1 0
Cheers, I've got a trek stache 7 and will be changing the uppers then from the cheap and heavy steel ones to lighter alloy ones. Just want to keep the offset the same for handleing.
• 1 0
Oooh. Might not be quite as simple as that. Essentially as long as the two crowns look identical when not fitted to the fork (same crown offset, same steerer/stanchion angles, same length stanchions etc), then your handling should stay the same. However, if the new alloy uppers come off a fork that also has an upgraded damper, then you may find your damper does not fit in the new crown.

At best it wont fit, at worst it will fit but be incompatible in some more subtle way that could lead to either a lack of damping (bad handling and possible crashes) or the lowers detaching from the uppers when you lift your front wheel (definate crashes, possible death)

Basically, you should be ok, but just make VERY sure there are no hidden issues before you do the job.
• 1 1
I've got my suspension guy doing the swop over (he's use to full strip downs and custom set ups), he will check everything and change anything if needed. If it looks like it won't work then I won't be doing it. cheers
• 1 0
sweet. sounds like you've got it all under control
• 1 0
@gotshovel: and how about those brackets around the feet....now that looks easy to step off the bike.
• 13 0
How does this all work in terms of DH bikes? Take the Fox 40 for example. It has a standard offset but you see it on all types of DH bikes with all different head angles. You see it on a stock bike with a 64 degree head angle and then you see WC guys running the same fork at 62 degrees.

Wouldn't running these slack head angles make the bike handle like shit without additional offset?
• 15 1
Good call^^^^ When pointed downhill, and with the fork lower in its stroke, the effect is a steeper head angle, so the steering of a DH bike is less affected by the extra trail and handles beautifully with 44mm of offset. On the flats, though, all the negative aspects mentioned in this article come dramatically into play. Well stated sino.
• 3 0
Aha! Thanks for explaining... Even if I don't absolutely require the knowledge, it still helps to ferret it away in my little brain.
• 6 0
I would say the reason is because DH riders want the stability afforded by a fork with a lot of trail and are less concerned about any slowness in the steering at lower speeds. DH racers are very physical in the way they work the bike - the lightness of the steering is not the first consideration for them. And there are a lot of other things that affect the way the bike handles. Shorter chainstays help to keep things agile. Or, maybe the steering is actually shit and DH riders just aren't aware of what they are missing.
• 1 1
I don´t know who drawed this, but I beleive there is a serious mistake. @RichardCunningham if the dropout moves up and back, the steering axis also does, you have not changed it in the drawing, the trail does increase but not in the way you have drawed it! if not please explain.
• 1 0
@RichardCunningham: So, If I were to replace the RS Revelation (46mm offset) off the 2016 stumpjumper FSR 29 with 67.5 deg HA, and replace it with a DVO Diamond, (51mm offset) would I ruin the handling of the bike?
• 7 0
Hey RC, you need to expand this into a discussion of how a bike of a given trail can initiate turns... i think we talked about this once at ODD.... i think ppl would find this very interesting... plus you could assign all kinds of homework and at home experiments...
• 8 0
So how do the new Marzzochi 380's claim to be 26'and 650B compatible? I've heard that 650B's fit in Fox 36'ers, how would it ride?
Does 650B truly make me taller, more financially secure and attractive to the opposite sex?
• 12 1
No, i bought a 650b bike and spent all my money, lost my girlfriend, and i sit down crying all the time because it didnt deliver on all the marketing promises

so it did none of those things
• 1 0
I ride a 36 with 650b in it. Rides beautifully .. Its a 160 lowered to 140 for my geo.. running dhf 3c maxxterra 2.3 .
• 9 0
Bloody hell... I learn new things today n i getting more confuse everyday
• 7 0
What will a 650b Pike with 26" wheels on a 68' head angle 26" bike handle like?
• 2 0
This something I'd like to know as well.
• 1 0
Then buy one and find out gents, we all are eager to hear the results.... Yoroshiku as we say over here.
• 5 0
Does that translate to: "just spunk £800 on a guess."
• 1 0
Exactly Zziplex, you got it! That is the choice we are all faced with unless we do the maths! So, after reading RC's little piece above why don't YOU think what it would handle like?
• 1 0
Sorry Dave, but what I think and what is the reality are potentially two different scenarios. It doesn't change the issue of potentially buying something that is unusable. Numbers need a context too, does 6mm in trail actually make a real world difference? I don't know, I'm not a bike guru, hence the question.
• 4 0
Fair enough Zziplex, I am with you on that one, definitely not a bike guru here either, however, my not very well made point (I suffer from that a lot on here!) is that I think many of us these days are very quick to want an answer and miss an opportunity to educate ourselves. RC's article really gives us all a chance to understand more about trail, offset, wheelsize and their relationship. I had a quick look and the offset for the Pike 650B is 42mm with an A2C (axle to crown) of 542 for the 150mm and 552 for the 160mm travel version. The A2C of a 26 inch Pike is 10mm less for each model and the offset is 40mm, so losing 2mm.

So, what if you put more A2C on a 26 inch frame? First, what will happen to HA? It will slacken ever so slightly since there is 10mm more A2C. (see this from Cotic to help you understand.. change the fork stroke (thus A2C) and watch the HA change www.cotic.co.uk/geek ). This will add to stability at high speed, on the steep bits and in the rocks but will lose you some finesse during slow control on tight turns.

What will happen if you put more offset on a 26 inch frame? Well, it will push the wheel out front, and lengthen the wheelbase. This will add to stability at high speed, on the steep bits and in the rocks but will lose you some finesse during slow control on tight turns.

So, if you put a Pike 650B on a 26 inch frame it will be making at least two adjustments to the ride, and both will be ensuring greater control and speed and on the steeps at the cost of some cornering and climbing ability... well, that is what the theory that I understand suggests.

As I said, I am not a bike guru however, it is great to try and think about it....
• 1 0
I agree totally with your theory, that's what I was thinking, but is it right.

More control going down, less going up is arbitrary though. How can that statement be measured? I bottled buying a 650b Pike and went for the 26" version as this detail is not available, this will cost me when I come to eventually upgrade to 650b, but I reckon I made the safe choice. I'd personally rather rely on expert opinion than base my own on bro science etc especially when the mistake could be an expensive one, but each to their own I suppose. Tight lines ;-)
• 1 0
Yeah, I hear you on the money front!!! Mistakes can be costly. I sometimes forget that I have the luxury here of Yahoo Auctions. I have been known to get hold of a fork from our favorite online purveyors of goodies and try them out against my "theories" of what "should" happen safe in the knowledge that if I make a mistake and have to sell the second hand slightly used fork on Yahoo over here, it gets me, as close as dammit, the same as what I paid for it. It does make it a lot easier to try things out. I reckon I would have done the same as you and gone for the 26 inch version too. I do have a bit of Pike envy though... I would love to try and try one out. They cost crazy money over here! Enjoy the rapidly approaching weekend Zziplex!
• 3 0
@orientdave there may be a small error in one of your comments. It is unclear exactly what you mean by "lose some finesse". Increasing offset speeds up steering and makes things more responsive at low speeds. It compensates for some of the effects you mention which do occur when the steering angle is slackened without any change to the fork offset. So why don't we all simply use 650B forks with the increased offset? The first reason is there is a tight relationship between fork offset and wheel radius. The steering of a 650B bike with 44mm offset and a 26in bike with 39mm offset will be very similar in function and feel for bikes with the same head/steering angle. The second reason is bikes are designed with particular forks in mind and it is not a good idea to fiddle with offset (i.e. increase it) unless you also are in a position to adjust the head angle (i.e. slacken it). The extra fork length is this case would not be a big enough factor by itself to achieve the slackening required and the steering of Zziplex's bike would end up being too quick at low speeds.
• 2 0
Thanks stillunimpressed! Thanks for help in clearing that up; by "lose some finesse" I meant that my control of the bike at low speeds would suffer (from the quicker steering).... So a genuine thanks for that.. this thread is one reason I enjoy reading things on PB. It really does, with everyone's help, help me (and lots more like me I am sure) to get a better understanding of our bikes and the ride.

Excuse the soapbox moment coming.... Sure, we could all just buy an off the shelf bike, based on reviews by the two PB Mike's or Steve Jones' of this world, however, and this for me is a HUGE point, there is so much meta-language used by bike and component manufacturers telling us about their "forward planted geometry" or "KS Gussetting" or "double-chutney-burning drop-link" that in the end, unless we try and educate ourselves as to what is happening with the geo of our bikes, we are at the mercy of the marketers. Thanks PB and all of you for helping me gain a better understanding of it all. Long may it continue.
• 2 0
You have made your point well and very amusingly. If you want to cut through that crap I can suggest no better place than linkagedesign.blogspot.com.es There is a vast amount of data and analysis there about actual bicycle suspension designs and the ever present danger of becoming enlightened about suspension geometry! You may need to use the provided translator.
• 1 1
When I hear people talking about lengthening their a2c, why not go ahead and get a fork with more travel? I personally prefer a slack head angle with the lowest stack height possible when running any fork 150 mm or longer.if I have less than a 67 degree head angle with a long fork, I like the lowest position for my grips. It helps a bike with a slack geometry corner faster and maintain a lower center of gravity.I wish companies would run the shortest A2c possible.
• 4 0
This is the type of article I like to see on PB. It is not a review hyping something. It is not an advertisement in disguise. It is informative. I am so tired of bike/component reviews that are useless (I have never read a negative review) and so tired of ads that are displayed as articles. The last bike purchase I made was tough because I could not find a single review that said on bike in the category I was looking at was better than another or had a single negative issue.
• 4 1
An article that might have educated a few people. There are all these multiple adjustable bikes out there, that so get 'pushed', yet this article seems to dismiss the use of adjustable TCs. Now there's a turn around....... Triple clamp off set, determined more by turning radius - yes, that's a fact. And a p*** oor one at that. MTBs, are so dominated by BS and marketing hype, yet a valid adjustment, is so easily dismissed. Well, I'm not surprised - a 'market' that so values hype and gimmick, yet seems to think rubber bumpers on fork legs are acceptable as a steer stop ......... seriously, gullibility is the heading you'd place most MTBers under.

Change the offset on a motorcycle, by as little as 1mm at the triple clamp, and you'll feel the difference. Now, the difference between a 40mm offset DH fork, and a 51 /54 - it's very, very pronounced. The only way such bad geometries on so many bicycles (of so many types) has been got away with, is lack of knowledge / feel by riders, their gullibility and "pride of ownership" in what they have bought, and, that even a relatively heavy, 40 + lb DH bike, is still a 'toy', that can be dealt with. That simple fact, allows dreadful designs, and geometry, to be accepted as the "bestest of things". Now, I favour less offset, for more trail, on both my Motorcycles and Bicycles, with less than chopperesque steering head angles, and with a good wheel base and chainstay / swingarm lengths. So, I'm 'different' to the seeming norm of kicked out front ends, with large (relative) offsets, short wheelbases, and short rear ends.
• 3 0
I was explaining this very thing to someone only last week. Like everything on a bike, it is 1 input of many that has an effect on steering. It is not a black and white science.
• 2 0
Finally someone that understand what bike is all about ,thank you RC ,cause many people say this and say that ,but they ignore that simple but still "simple"things can make a real difference on what a bike "feel" and behaves ,and they could not understand what it is. BRILLIANT JOB. There are others , it might take a professional to realize that but it is good for a simple rider to know for not take anything for granted. KEEP ON GOING,CAUSE ITS PEOPLE LIKE YOU THAT MAKE US GROWN IN
• 1 0
So lets say your bike is not new. Perhaps the HT angle is a bit steep.
Replace the front fork and wheel with a 27.5 fork and wheel.
26 inch wheel in the back 27.5 up front will give you about one half of a degree of extra" slack" to make your bike more DH friendly.

Or if you want to mess with peoples heads put a 29 set-up up front with a 26 inch wheel in the back.
Manny possibilities.
Too bad you cant order custom off sets for your fork to dial in the amount of trail.
• 1 0
the only problem with adding front wheel diameter is that you keep cranking your bottom bracket higher and higher. running a lower volume rear tire helps lower the bottom bracket a little, and running a large-volume front tire helps slacken the head angle without raising the front axle and bottom bracket as much then I got as a larger diameter wheel
• 1 0
Why not just get a 650b fork and put your 26inch wheel in it? You should get the offset without raising your bb. Trek made the 69er a long time ago, those who had them really loved them but it didn't really catch on with the masses.
• 1 0
I dont understand any of this shit.....but Im old enough to remember decades ago when Honda made those motorbikes with really big front wheels and standard small rear (23 inches sticks in my brain for front and 17 inches for back when everyone else was running 21/17) and then I thought about that Mexican dude who was shredding on movies for monday with a 24 inch rear wheel when his 26 inch one broke.......I keep saying it is the next logical step when Giant runs out of puff pushing 650b on us all-different wheel sizes.......cant swap tires from front to rear and vice versa-win win for all the manufacturers-sell more shit and we get more explanations how it can be much better...blah blah.
All I wanna do is ride-too hot though-f*ck 40 degrees tomorrow (centigrade)-wish it was wet and cold-lucky northern hemisphere dudes.Bring on winter.....
• 1 0
@aztrak2010, the 650b fork would just cheat you out of 10 millimeters of suspension travel, given the difference in a2c. If you want to add offset to quicken the steering, why run a slacker head angle to begin with? the difference in wheel size would also create a big jump in the effective offset, even tho the numbers on paper look very similar without considering wheel size.
• 1 0
That was well written^^^
• 1 0
Thanks ShopMechanic, that was really helpful
• 1 0
@optimumnotmaximum: Happy to help!
• 2 1
Cool to know. I saw something about this in a bike class video once. The host demonstrated trail by turning the fork around to create more trail and then pushing the bike. It went a long ways without falling over.
• 11 0
i was literally just about to comment saying "im going to go put my forks on backwards and ride about no handed for a bit, i blame you guys if i come back with a bloody nose" but now thanks to your comment i don't have too. thankyou. even though i believe what you say... i still somehow feel you saved me from a bloody nose.
• 3 0
LOL!
• 1 0
Makes me wonder what kind of effect it will have on my bike since i just swapped a Fox Van for a Boxxer WC. They have practically the same A2C, not sure about the offset though.
• 7 0
Boxxer will be a little lower due to the extra travel. I don't think mortals can feel the difference.
• 1 0
Offset will change with wheel size.
• 1 0
So if I want to switch from 140mm to a 150/160mm fork I shouldn't have to worry about offset?
• 2 0
Correct, only head tube angle and bb height should be your concerns. Neither of which would concern me.
• 3 0
this makes me wonder if I've been a complete retard every time i build a bike.....
• 1 0
Jonsson5: I hear you! think of it as a learning process. Looking back on the bikes I have built up, I have got it right sometimes (Cotic BFe with a Pike 454 U-turn, Blindside V1 with a Manitou Intrinsic 180mm, both of which matched where I ride seemingly perfectly) and then again very wrong sometimes (Bottlerocket with a U-turn Domain 318, Uzzi with a Boxxer WC which didn't match where I rode them)... however, each time I am learning more about how the frame / fork combination works together. That is one reason why I am sticking to 26 inch: I am more likely to get something that feels right these days!
• 1 0
Interestingly the recent trend for offset headsets and shock bushes might considerably affect the bike handling if account isnt taken for fork offset.
Does this make our enthusiastic geometry dabbling badly informed?
• 2 0
www.pinkbike.com/news/To-The-Point-Rake-and-Trail.html

Reduce, re-use, recycle…

(yes, I get that they add wheel size to this one.)
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(Linked at the bottom of story)
• 1 1
So what would be the effect of running a 26" wheel in a 27.5 fork? I'll be getting a Pike soon for my 26" all mountain bike and thinking of getting the 27.5 model so I don't need to change it if/when I switch to 27.5 wheels in the future, and the extra axle-to-crown length will be a bonus to slacken the head angle out slightly. Will the increased trail give marginally heavier steering or cause real problems?
• 1 0
So If I want to upgrade my QR Fork (SID 120mm) to a beefier 130-140mm 15mm axle fork (tapered) I could potentially need to invest in an adjustable headset do deal with trail?!
• 1 0
On the 27 side, isn't X-Fusion the only one to provide more offset on their 27 forks (48mm I believe), whereas Rockshox and Fox are still keeping it the same as 26 at 46mm???
• 4 0
IIRC, 26"= 42mm, 27.5" = 46mm, 29" = 51mm.
Also I found that Fox varies by model...The 26" 36 has less offset than the 26" 32.

It would be nice if all fork makers consistently published the offset and AtoC with the fork specs.
• 1 0
I got the numbers wrong then…but again, isn't X-Fusion the only one offering a longer offset on their 27" fork vs. 26"? I remember reading this somewhere. Or are Fox, RS, and XF all using a 46mm offset on their 27 forks?
• 1 0
I think the Dorado has seperate offset
• 1 0
Fox 40 26 and 27.5 have different offsets though I dunno if you can get your hands on a fox 40 27.5 for 2014...
• 3 0
Thanks RC, very informative.
• 3 1
Color code figures based on wheel size and they will be much easier to understand.
• 1 0
And so,...some will say a @67º ha on a 650b is equal to 66º of a @26"...so is trail the reason for this, or claim not valid?
• 1 0
It's to do with weight of steering created by trail. Most forks in the same catergories use the same offset which is why HA is more important because trail is affected by those two things.
On average yes a 26" will have the same trail as a 1 degree steeper 650B for the same catergory of fork which leads to a similar weight of handling which is what gives you a bike in the same part of the stability to turnability scale.
Trail is the thing that matters, but is adjusted by HA and offset is the short version.
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@Tristanssid is correct, mechanical trail is the key determinant of steering function and feel and it is affected by both HA and offset. Still there is a problem with claim you mention @jrocksdh. If you use a fork with a 39mm offset on a 650B bike, which (all other things being equal) will result in sluggish steering at low speeds, you necessarily have to sharpen the head angle in order to have the bike steer like its 26in counterpart. But 650B bikes aren't meant to use 39mm offset forks (designed for 26in bikes). The common offset for a 650B fork is 44mm and the trail on a 650B bike using that fork will be nearly the same as that on a 26in bike for bikes with the same HA. So, 26in and 27.5in bikes steer pretty much the same with the same HA because they were always meant to, and do, use forks with different offsets. The claim is kind of irrelevant because fork and bike designers will (in time) change whatever is required to give the head angles and steering speed that they are after.
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i rode a raliegh grifter so i already know.....
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I plan to buy a kona process 111 (29er) and add a pike. the revelation of the bike comes with has 46mm offset. Now i am wondering if I should buy a 51mm offset pike or the 46mm model. the process is slack, so considering the article 51mm should be the way !?
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Like the article said, the manufacturers usually get it right so i wouldn't mess with it (and kona seems to have especially dialed it in on the process line). Or if you ride the bike with the 46mm offset revelation and the steering feels too slow THEN maybe think about getting the larger offset for less trail and more nimble handling.
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i would guess that using a fork with the trail that the bike was designed for is probably the best idea. the axle to crown on those two forks is different i think, so that will change things too...
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I could get a really good deal on the pike along with the bike, so I was thinking of adding a bigger fork right from the beginning. maybe i will see how it rides....

@parallaxid: the traveled pike ist just 3mm higher compared with the revelation (Chris Mandell rides a pike in his 111....but i have no idea which one)
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Can you repeat that in english?
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The article says "More offset equals less trail."

This does not seem correct. If offset is the distance from the center line of the stanchion, to a line parallel to the axis of the stanchion, but through the axle, then the farther you move that axle from the stanchion, the trail on the ground increases. So then increasing offset would increase trail, per the first figure in the article?

This seems to contradict with "trail increases with wheel size"???

Not sure what I am missing.
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The trail will decrease as you move the dropout farther away from the lower leg. If you looks at the first diagram they are showing a 29er fork with an increased offset, the result is the axle falls in the same plane as the 26er dropouts. The second diagram is just illustrating how trail does increase with a 29er fork that does not have an adjusted offset.
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More off set more trail. Why? The axel trails in front of the axis line of the station tubes.
The fork crown off set also plays a role in how much trail a fork has.
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By increasing the off set you decrease the trail, not increase it. Yes, the fork crown can also affect the trail measurement of the front tire, along with a couple other variables.
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Had to look at a few other diagrams to get the picture. And yep more off set at the axel equals less trail. A slacker head tube gives you more trail.
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So many guys will now be blaming crap runs on offset and trail....
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boring, it is obvious cases, any bike mechanic know's it
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Just get out and ride!!!!
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Agree Brett7-all I know is my bike is really shit without wheels-keep going over the handlebars because the forks dig into the dirt.....put wheels on and voila and it goes-26, 27.5 or 29-they all seem to work. And the more time I ride with wheels on the better I become......just a thought.
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can we have a live Q&A video chat with you RC?!??!
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I just want to chill and ride my bike. Let's stop worrying about wheels.
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It's not solely focused to wheels- it's about handling. If you change out the crowns on your fork or swap to a different fork that has different crowns/offset/trail, then you can better understand how it will affect your ride.
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I just ride the bike
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for now.
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great article!
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Very interesting.
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"27.5 was excluded to more clearly illustrate the contrasts" - making 650b really not all the holy grail of sizing it markets itself to be.
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Wut? How it is related in any form or shape?