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Discussion Starter · #1 ·
The latest 29" bike I built up used a shorter 42mm offset fork, has a 66.5 HTA, and a 50mm stem. Of course there are a lot of variables but I'm convinced I can feel a difference. On high speed, hard, sweeping corners the bike feels better. Less twitchy, more locked into the turn, more confidence inspiring. High speed cornering has always been my weak link and I'm convinced I feel better on this bike. Otherwise no drawbacks noted elsewhere. Travel is 130mm up front.

My other bike is a 275 wheel with the same HTA, stem (even same bars), similar reach. Just a bit more travel. 150mm up front. If I were putting a new fork on ths bike, if I wanted a similar feel, what offset would I be looking at? I presume a relatively shorter offset? Currently running what I believe is a 46 or 44mm and I do like the handling. Some forks available now are as short as 37mm offset. Any ideas? Not saying I'm changing the fork, just thinking about offset, and got the flu with too much down time.
 

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I'm running a 37mm offset Pike on my Endo, accidentally as it arrived like that when I ordered it despite no mention of offset on the website. I put an offset bushing in the rear shock to slacken it out a little to recover some of the wheelbase and have since taken that out and put a -1* angleset in. I agree with your findings, and although I'd need to do some back-to-back trials to be sure I feel like with the changes I've gained in some areas without losing in others.
 

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Depends on geometry and personal preference. I recently switched bikes (both 29ers) with a 46mm offset fork: one felt normal while the other felt borderline twitchy. I switched to a 51mm offset fork on the bike that felt twitchy with a 46, and the bike handles more comfortable and predictable.
 

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orthonormal
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The latest 29" bike I built up used a shorter 42mm offset fork, has a 66.5 HTA, and a 50mm stem. Of course there are a lot of variables but I'm convinced I can feel a difference. On high speed, hard, sweeping corners the bike feels better. Less twitchy, more locked into the turn, more confidence inspiring. High speed cornering has always been my weak link and I'm convinced I feel better on this bike. Otherwise no drawbacks noted elsewhere. Travel is 130mm up front.

My other bike is a 275 wheel with the same HTA, stem (even same bars), similar reach. Just a bit more travel. 150mm up front. If I were putting a new fork on ths bike, if I wanted a similar feel, what offset would I be looking at? I presume a relatively shorter offset? Currently running what I believe is a 46 or 44mm and I do like the handling. Some forks available now are as short as 37mm offset. Any ideas? Not saying I'm changing the fork, just thinking about offset, and got the flu with too much down time.
Cut and paste from Knolly's Fugitive LT page (https://www.knollybikes.com/fugitivelt)

Fork offset for the Fugitive

Recently there has been a lot of talk about fork offset in the bike industry. The simple truth is that you can run either offset on our Fugitive (or any bike) - you just need to understand how the bike will ride with a shorter or longer offset fork.

With a longer offset (51mm) the bike corners better in tight singletrack and has slightly quicker handling but it gives up a bit of stability at high speed.

In the shorter offset (42 to 44) the bike is more raked out so it is more stable and performs better at high speeds but in tech climbs, switchbacks, and slower stuff, the bike is a bit more to get around and the front end can feel floppy.

Depending on travel, a shorter offset will change the wheelbase between 5-7mm which amounts to an almost insignificant half a percent (0.5%) of the total wheel base.

As with all geometry changes, advantages in one area are achieved at the sacrifice elsewhere. Fork offset is a simply another tool/adjustment for riders to customize the handling of the bike to suit their riding style and the terrain they ride.
 

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In the shorter offset (42 to 44) the bike is more raked out so it is more stable and performs better at high speeds but in tech climbs, switchbacks, and slower stuff, the bike is a bit more to get around and the front end can feel floppy.
The first ride I did with the new fork was a trail that has a mix of tight and twisty tech (both flat and dh) along with a couple of steep chutes and I found the handling in the tighter corners at slower speeds to be more "deliberate" (I'm no good at converting what I perceived into words). It was like the bike did require a little more effort to manoeuvre but not in a bad way, like it was harder to over-steer and easier to point-and-shoot. Perhaps slackening out the front end in conjunction with the reduced offset helped? I should have tried it without the bushing first I guess, but I think knocking another half a degree off with the angleset improved things again. Not to question Noels wisdom or anything, but I guess it's all subjective to personal preference and experience really...
 

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Short-Change-Hero
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So I recently did this...
2019 GG The Smash came with 51mm offset Yari RC at 150mm. Bike felt great with the offset and travel, main thing being that in fast cornering in flowy sections I felt like the bike had to be slammed over to really get fast corners. Like it loved to be leaned way into a corner but never gave up grip.

Switching to the 42mm offset Lyrik last ride has shown that the same sections do not require as much "body english" to corner like the Yari did. Still felt quite stable at speeds but just did not need quite as much bodily input to carve the corners. Doesnt feel twitchy or anything like that, the 51mm seems to "like" oversteer more than the 42mm offset but that could just be in my mind. I have a larger ride tonight that I did last week on the Yari (51mm) so I will have a bit better of a comparison.
 

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orthonormal
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The first ride I did with the new fork was a trail that has a mix of tight and twisty tech (both flat and dh) along with a couple of steep chutes and I found the handling in the tighter corners at slower speeds to be more "deliberate" (I'm no good at converting what I perceived into words). It was like the bike did require a little more effort to manoeuvre but not in a bad way, like it was harder to over-steer and easier to point-and-shoot. Perhaps slackening out the front end in conjunction with the reduced offset helped? I should have tried it without the bushing first I guess, but I think knocking another half a degree off with the angleset improved things again. Not to question Noels wisdom or anything, but I guess it's all subjective to personal preference and experience really...
Both of those changes affected trail, which is the distance between the contact patch of your front tire (directly below the axle center) and where a line drawn through the center of the head tube contacts the ground.

Decreasing the fork offset with the head angle constant moves the contact patch rearward while the head tube line stays the same so trail increases and so does stability. Slackening the head angle pushes both the head tube line and the contact patch forward but it pushes the head tube line more so that also increases trail and stability.
 

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Keep on Rockin...
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Discussion Starter · #9 · (Edited)
Thanks for the input.

So, specifically, two bikes with the same set up and angles, except ones a 29 and ones a 275...

To get the same relative feel on the 275 I got with going to a relatively short offset 29, 42mm, should the offset on the 275 be relatively shorter? Like maybe going with a 37mm on the 275? (Compared to the 44 I have now.). I should _not_ be looking at going up in rake on the 275, correct?

I'm pretty sure I'm correct on this, it's just that 37mm seems quite a bit shorter than I'm use to seeing.

While we have plenty of tight, slow techy bits, I grew up biking on that, so I need no extra help there. It's the high speed sweeping turns and berms where I could use a extra help.
 

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This video had a pretty good description of what the difference made when mounting different offset forks and the "perceived" change was.

Last night riding the same route that I did last week on monday, but tonight with the 42mm offset Lyrik, I found that steering to be a bit quicker and tighter. In fast sections this meant that the bike did not have to be leaned over near as far or take as much input (body english) to make the turns. This isnt to say that the 51mm was "slower" it just did not take as much to turn the bike. However, the biggest drawback feeling was in the slower, tight corners (down switchbacks or climbing slow switchbacks) I did feel like the bike needed MORE turning of the wheel and less leaning to get the turns right.

Really nothing huge, just a slight change in how you ride is all. I plan to ride the Lyrik for a season or two and will pick up a Manitou Mezzer when I can find one for a good price as I have REALLY been wanting a long travel Manitou 29er fork for ages (since riding my Tower Pro and a demo ride on the Mattoc Pro). When I do go for the Mezzer I will probably go with the 44mm offset version.
 

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...with the 42mm offset Lyrik, I found that steering to be a bit quicker and tighter. In fast sections this meant that the bike did not have to be leaned over near as far or take as much input (body english) to make the turns. This isnt to say that the 51mm was "slower" it just did not take as much to turn the bike. ...
Your experience is counter to the conventional wisdom. Less offset means more trail, which is usually taken to mean better high speed stability, slower steering and floppier front end making it less maneuverable it tight stuff.
 

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orthonormal
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Thanks for the input.

So, specifically, two bikes with the same set up and angles, except ones a 29 and ones a 275...

To get the same relative feel on the 275 I got with going to a relatively short offset 29, 42mm, should the offset on the 275 be relatively shorter? Like maybe going with a 37mm on the 275? (Compared to the 44 I have now.). I should _not_ be looking at going up in rake on the 275, correct?

I'm pretty sure I'm correct on this, it's just that 37mm seems quite a bit shorter than I'm use to seeing.

While we have plenty of tight, slow techy bits, I grew up biking on that, so I need no extra help there. It's the high speed sweeping turns and berms where I could use a extra help.
If you want to plug some numbers into a calculator, you can use this:

trail = [wheel_radius*cos(head_angle) - fork_offset]/sin(head_angle)

So if head angle stays the same and fork offset stays the same but you move from 27.5 to 29, trail increases. The move to 51mm offset for 29ers happened initially because Trek/Fisher wanted to compensate for the increased trail brought about by the move from 26 to 29. Other manufacturers like Niner were selling bikes with 72 degree head angles. Crazy solutions to legitimate problems.

My current bike (Knolly Fugitive LT) has 111mm trail with a 66 degree head angle and 51mm offset fork. Decreasing offset to 44mm increases trail to almost 119mm. I could get almost the same exact trail number by using a -1 degree angleset with the the 51mm offset fork but the wheelbase would be longer and the BB would be lower and those changes would affect the bike's handling as well. Complicated stuff.
 

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Your experience is counter to the conventional wisdom. Less offset means more trail, which is usually taken to mean better high speed stability, slower steering and floppier front end making it less maneuverable it tight stuff.
Right.. and that is what I have been reading/watching. But for me I really don't notice that large of a difference between the too. It could also be how the particular bike handles. For me, the Smash likes to be really leaned over in corners, regardless of how tight they are. I feel that it turns "better" when there is more steering input vs. not. The "flop" or anything is not something that I really noticed but then again I only had 90 miles on the bike before I changed the fork, so really it could have been that. Also, the Yari stock MoCo damper was garbage for my trails so I was definitely more focused on keeping my teeth in my head vs. other things.

Again, I have only ever ridden 51mm offset forks on my 29ers and had less than 100 miles on this one before I swapped. If I changed it on my old trail bike I may notice it more as I have YEARS and thousands of miles on that bike so a little more in tune with how it handles, steers, etc.
 

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Discussion Starter · #15 ·
If you want to plug some numbers into a calculator, you can use this:

trail = [wheel_radius*cos(head_angle) - fork_offset]/sin(head_angle)

So if head angle stays the same and fork offset stays the same but you move from 27.5 to 29, trail increases. The move to 51mm offset for 29ers happened initially because Trek/Fisher wanted to compensate for the increased trail brought about by the move from 26 to 29. Other manufacturers like Niner were selling bikes with 72 degree head angles. Crazy solutions to legitimate problems.

My current bike (Knolly Fugitive LT) has 111mm trail with a 66 degree head angle and 51mm offset fork. Decreasing offset to 44mm increases trail to almost 119mm. I could get almost the same exact trail number by using a -1 degree angleset with the the 51mm offset fork but the wheelbase would be longer and the BB would be lower and those changes would affect the bike's handling as well. Complicated stuff.
Doing the math trail is about the same on a 275 with 37mm rake vs a 29 with 42mm rake. All else being equal.

So, yep, that's what I'm going for.
 
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