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Fork offsets matter less on short travel?

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RacerLex

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Discussion starter · #1 ·
Is the difference between 44mm and 51mm fork offsets on modern short travel (120mm) 29er bikes negligible?

There are steep discounts on 51mm offset forks and I’m wondering if the savings are worth the “compromise.”
 
#3 ·
IME, the difference between 44mm and 51mm is more noticeable on steep short travel bikes, with the long offset greatly preferred. Long offset gives the bike more stability and more direct and intuitive handling. Short offset makes the bike feel lazy.

On slack long travel bikes, I don't really notice much of a difference to have any preference. Hard to generalize, since the slack HTA with long fork dictates more of the handling feel than the offset. Forces you to lean, even at low speeds. Steering seems to be strongly discouraged. Offset doesn't really change this. Seems tall people prefer shorter offset, since it brings the front wheel back, adding back a minimal amount of handling traits of a more compact bike.

In theory, longer fork offset enables slacker HTA, retaining similar steering characteristics of a steeper HTA bike, but bikes are already kind of long and a longer offset makes it longer. A Fox 40 DH fork has an offset of 56mm, I believe. I recall Cannondale having a long travel Supermax Lefty with 60+mm offset.
 
#4 ·
If you gave me a fork without telling me the offset and let me ride it around for an hour or 2 I wouldn't be able to tell you whether it's a 44mm or 51mm offset. If you gave me 2 otherwise identical forks with different offsets and I ride them back to back for a couple hours then I could tell that one of them turns in a bit better than the other and that's about it for me. My preference would be for the longer offset since it turns in a touch faster, but to me it's a pretty small difference that's only noticeable in A/B testing and could easily get swamped out by a 2psi change in tire pressure.
 
#5 ·
Varaxis said:
IME, the difference between 44mm and 51mm is more noticeable on steep short travel bikes, with the long offset greatly preferred. Long offset gives the bike more stability and more direct and intuitive handling. Short offset makes the bike feel lazy.

On slack long travel bikes, I don't really notice much of a difference to have any preference. Hard to generalize, since the slack HTA with long fork dictates more of the handling feel than the offset. Forces you to lean, even at low speeds. Steering seems to be strongly discouraged. Offset doesn't really change this. Seems tall people prefer shorter offset, since it brings the front wheel back, adding back a minimal amount of handling traits of a more compact bike.

In theory, longer fork offset enables slacker HTA, retaining similar steering characteristics of a steeper HTA bike, but bikes are already kind of long and a longer offset makes it longer. A Fox 40 DH fork has an offset of 56mm, I believe. I recall Cannondale having a long travel Supermax Lefty with 60+mm offset.
Click to expand...
I'm going to have to disagree, the shorter offset will give you more stability by increasing trail, the longer trail will give you more self centering steering in turn making the bike want to keep going straight. A long travel bike with less say a 64⁰ HA and 44 offset souks be as stable as a bike with a 63⁰ HA and 51 offset so by going with the shorter offset you get the stability of a slacker HA without the increase in wheelbase.
The longer offset will give you a quicker steering by reducing trail and on a slack bike will increase wheel flop. On a short travel bike the choice IMO will depend on what your trails look like, do you ride mostly tech will right turns? The the longer offset might be the better choice but if they are flowy and fast then the shorter offset might be the better option. But we are talking about minimal differences here so I'm pretty sure after a few rides you'll get used to either offset so if the deal is good enough then i would go with cheaper fork. My 2 cents
 
#7 · (Edited)
Blkdoutindustries said:
I'm going to have to disagree, the shorter offset will give you more stability by increasing trail, the longer trail will give you more self centering steering in turn making the bike want to keep going straight. A long travel bike with less say a 64⁰ HA and 44 offset souks be as stable as a bike with a 63⁰ HA and 51 offset so by going with the shorter offset you get the stability of a slacker HA without the increase in wheelbase.
The longer offset will give you a quicker steering by reducing trail and on a slack bike will increase wheel flop. On a short travel bike the choice IMO will depend on what your trails look like, do you ride mostly tech will right turns? The the longer offset might be the better choice but if they are flowy and fast then the shorter offset might be the better option. But we are talking about minimal differences here so I'm pretty sure after a few rides you'll get used to either offset so if the deal is good enough then i would go with cheaper fork. My 2 cents
Click to expand...
Your facts are off. Wheel flop is decreased with more fork offset. In other words, more mechanical-trail = more flop.

The stability comes from wheelbase increase. Long offset = longer wheelbase.

"Steering stability" comes from the rider's familiarity with the strength of the bike's self-centering. Low familiarity = twitchiness. Even a slack bike like a Grim Donut will feel twitchy and unstable until a rider becomes familiar with its steering characteristics.

As you say, a rider will become accustomed to changes in steering feel, so it arguably doesn't matter how much steering stability you have. Can be running Canyon's KIS or be running with a fork backwards for extra steering stability (not real stability), but what matters more is your familiarity. The offset tweaks altering geo and wheel flop are also worth considering more than the questionable concept of steering stability.

I say there's more effect with steeper short travel bikes because a 7mm change in trail is a bigger percentage of change when the bike's trail is 90mm, compared to a slack long travel bike's trail of 130mm. I also believe one's more likely to notice a performance difference from a longer wheelbase's stability than any steering stability.

I also believe that shorties are more likely to be open to that 63° HA with 51mm offset, over 64° HA with 44mm offset, since their frame size would already have a shorter WB due to a shorter reach. This is why I mention tall people preferring shorter offset--long wheelbase bikes probably have a front end length that is too long relative to the rear-end/chainstay length. There's a sweet spot balance point regarding weight distro that you can use offset to tune.
 
#8 · (Edited)
Varaxis said:
Your facts are off. Wheel flop is decreased with more fork offset. In other words, more mechanical-trail = more flop.

The stability comes from wheelbase increase. Long offset = longer wheelbase.

Steering stability comes from the rider's familiarity with the strength of the bike's self-centering. Low familiarity = twitchiness. Even a slack bike like a Grim Donut will feel twitchy and unstable until a rider becomes familiar with its steering characteristics. With weaker self-centering from less mech-trail, the rider fills in with stability.

As you say, a rider will become accustomed to changes in steering feel, so it arguably doesn't matter as much. Can choose offset based on the tweaks to geo and wheel flop amount. There's also the superstition about offset being good if it matches the stem length.

I say there's more effect with steeper short travel bikes because a 7mm change in trail is a bigger percentage of change when the bike's trail is 90mm, compared to a slack long travel bike's trail of 130mm. I also believe one's more likely to notice a performance difference from a longer wheelbase's stability than any steering stability.

I also believe that shorties are more likely to be open to that 63° HA with 51mm offset, over 64° HA with 44mm offset, since their frame size would already have a shorter WB due to a shorter reach. This is why I mention tall people preferring shorter offset--long wheelbase bikes probably have a front end length that is too long relative to the rear-end/chainstay length. There's a sweet spot balance point regarding weight distro that you can use offset to tune.
Click to expand...
Sorry, you are right about the flop, I wrote it backwards but stability part is correct imo but can agree to disagree. Here is directly from cane creek.
"Here’s the skinny: 51mm offset reduces “trail” and adds turning agility, while 44mm offset adds “trail” and adds straight-line stability, especially at high speeds"
Also IMO you'll notice the change in trail way easier than the wheelbase change, a 7mm trail change is about a 6% change vs a 7mm wheelbase increase in a 2000mm wheelbase is less than 0.5% change.


 
#9 ·
Blkdoutindustries said:
Sorry, you are right about the flop, I wrote it backwards but stability part is correct imo but can agree to disagree. Here is directly from cane creek.
"Here’s the skinny: 51mm offset reduces “trail” and adds turning agility, while 44mm offset adds “trail” and adds straight-line stability, especially at high speeds"
Also IMO you'll notice the change in trail way easier than the wheelbase change, a 7mm trail change is about a 6% change vs a 7mm wheelbase increase in a 2000mm wheelbase is less than 0.5% change.


Click to expand...
That's just a subjective take by one author.

Here's my take: riders can tell the difference between a size med and size large frame of the same model and spec level.

What's different between the two that can cause this? The 40mm difference in seat tube length isn't as likely as the 25mm increase in reach. I recall when everyone was feeling that upsizing gave more confidence to carry more speed through the rough. I credit the longer front-center for that confident feeling. That 7mm of offset can offer some of that.

For someone riding a bike with too long of a front-center, shortening the offset counters that. For example, Chris Porter of Geometron ran tests with various fork offsets. He liked shorter offsets, finding that they gripped better in corners. The guy is super tall. Seb Stott, another super tall rider, repeated his tests and found similar conclusions, with shorter offset feeling lazy, and feeling shorter in WB to the point that he lost confidence (unnerved), but finding that it found traction to carve better.

www.bikeradar.com

Pushing the limits of fork offset: an experiment | BikeRadar

Going beyond head angles into the nitty-gritty of MTB geometry
www.bikeradar.com www.bikeradar.com

Seb Stott doesn't preach offsets these days. He preaches size-specific chainstays. The front-center and rear-center balance has a huge effect. Since you can't tweak the rear-center, tweaking the front-center is your remaining option. Offset is one way to do that, besides headsets that tweak HTA and reach.
 
#10 · (Edited)

Transition SBG (Speed balanced geo) is what I believe popularized short offset.

Transition opts for a short offset to purposely increase mechanical trail, seemingly. As a small bonus, they get more front tire traction from shortening the front-center.

IMO, they have the balance between FC and RC well dialed in their size large frames. Since they shorten the FC/reach in their smaller frames, without also shortening the RC/chainstay, the front has even more traction. While some might think that's a good thing, I'd disagree. This is what I call being "front-heavy" (weight distro wise).

For casual use, like how one would drive a commuter car, front-heavy weight bias is fine. For high performance track use, I'd prefer something like a Porsche 911 with more rearward weight bias (60:40 rear:front, rather than closer to 50:50). The engine on a 911 is situated more rearward, rather than under the front hood. On a bike, this would be akin to a rider shifting their own weight rearward. IMO, a rider in a rearward-scooted position can't control the bike as well as they would in a more neutral/centered athletic position (note: this is measured according to the pull of gravity, going by how far the ass is behind the feet, not by how far the ass is behind the saddle). Instead of moving the rider rearward, why not move the wheels forward, so it's akin to having the weight more on the back? That's what happens when the front wheel gets moved forward by slack angled long forks and longer reach, and that's what I credit for the increase in confidence.

I blame "front-heavy" weight bias (any less than 60:40) on a lot of OTB crashes. You know that feeling of that front wheel dropping immediately on a drop, rather than staying level mid-air? That happens less on a more rear-biased weight distro.

IME, the perfect balance point is very narrow, but very worth chasing after, to the point I would purposely pay attention to the difference of how frames would handle in different sizes. Like I'd recommend a SB150 in size Med, but not in size Small, Large, or XL. I'd recommend a Meta AM 29 in size small, but not Med or Large. I'd recommend a Meta SX in size large, but not any other size. Most of Transition and Santa Cruz I'd recommend in size L. XL/XXL riders probably are finding relatively steep HTA bikes to be more intuitive and versatile, due to better balance points, or scoping out bikes with relatively long chainstays, like Niners.

As I mentioned before, short offset and slack HA make the steering characteristics change, to force leaning instead of steering. This is good for carving. This is flow trail territory, IMO. For janky tight trails, people without high level skills are more likely to be hanging their ass back, modulating their brakes, and maybe steering at low speed. This is where steep HA and longer offset shine more.
 
#12 ·
jeremy3220 said:
Shorter offset increases trail though.
Click to expand...
The facts I stated are consistent with that.

Short offset = more trail.

More trail = more flop.

More offset = less trail.

Less trail = less flop.

More offset = less flop.

Wheel flop is decreased with more fork offset.


Image


When you turn the wheel, the part of the tire that rests on the ground is the part marked by the red line here, rather than the part of the tire directly under the axle. The bike "falls" into that position (axle physically lowers). This vertical height difference is the cause of the flop sensation.

Increasing the offset closes the distance that the contact patch trails the steering axis.

Don't mind the picture's inaccuracy with the line drawn through the leg (I understand there is offset in the crown). I grabbed this pic off the net since I wanted to emphasize the height difference between the two tire contact points.
 
#13 ·
It barely makes a difference. In a year or so fork manufacturers will find something else to tweak by +/- 5mm and suddenly the old standards will be obsolete and unrideable.
 
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#14 ·
IMO unless you're on the edge of a handling problem you won't even notice.

I've swapped between both on 170mm travel forks and the only time I noticed a significant difference was requiring more muscle in rock rollover situations where the contact patch moves a long way rearward compared to normal riding.
 
#16 · (Edited)
alexbn921 said:
Depends on the balance of the bike. On a small you want more offset and on an xl/XXL you want less
Click to expand...
I disagree. If you tried to simplify what I posted earlier, then I have to say that you did not comprehend it correctly. I simply stated that two sizes of the same bike can handle differently on the trail, and that was due to the front-center difference. I implied the fork offset could be one of the ways to tweak that FC difference, along with headsets that tweak reach or HA, as well as diff fork length.

You'd be closer to what I meant, if you said that bikes with too little rearward weight bias (excessively short FC) want more fork offset, and bikes with too much rearward weight bias (excessively long FC) want less. There's a very large number of XL/XXL bikes that have too little rearward weight bias and can use long offset (mostly short travel bikes). On rare occasion, some bikes have so much rearward bias that their small size can use short offset (e.g. Honzo ESD, Fuji Auric LT, latest Canyon Strive).

7mm of fork offset only offers a very small effect for people chasing very marginal gains. You'd have to have a fine understanding and fine tuned sense to feel like one offset option has a performance advantage over the other. The money savings is more than enough reason to go with one over the other.

IIRC, 51mm offset was originally brought to market through Gary Fisher G2 geometry, to make it so a 29er 100mm bike with 68° HA had a familiar/consistent steering feel compared to a smaller wheeled 100mm bike with 68° HA (with shorter offset fork).
 
#17 ·
I've run both offsets on the same bike. As others noted, the difference is subtle and I adapted almost instantly. I actually notice a bigger handling difference raising or lowering my stack height by a measly 5mm than I did changing offset.

Of all the handling/fit variables you can tweak, offset is the one I'd spend the least amount energy worrying about.
 
#18 · (Edited)
Varaxis said:
I disagree. If you tried to simplify what I posted earlier, then I have to say that you did not comprehend it correctly. I simply stated that two sizes of the same bike can handle differently on the trail, and that was due to the front-center difference. I implied the fork offset could be one of the ways to tweak that FC difference, along with headsets that tweak reach or HA, as well as diff fork length.

You'd be closer to what I meant, if you said that bikes with too little rearward weight bias (excessively short FC) want more fork offset, and bikes with too much rearward weight bias (excessively long FC) want less. There's a very large number of XL/XXL bikes that have too little rearward weight bias and can use long offset (mostly short travel bikes). On rare occasion, some bikes have so much rearward bias that their small size can use short offset (e.g. Honzo ESD, Fuji Auric LT, latest Canyon Strive).

7mm of fork offset only offers a very small effect for people chasing very marginal gains. You'd have to have a fine understanding and fine tuned sense to feel like one offset option has a performance advantage over the other. The money savings is more than enough reason to go with one over the other.

IIRC, 51mm offset was originally brought to market through Gary Fisher G2 geometry, to make it so a 29er 100mm bike with 68° HA had a familiar/consistent steering feel compared to a smaller wheeled 100mm bike with 68° HA (with shorter offset fork).
Click to expand...
A bike in xxl size has a long front. Most still have the same rc. This means more weight on the back tire. always heavy feet and Light hands.

i suggest we all read this


www.bikeradar.com

The ultimate guide to bike geometry and handling

Getting into the details of why no two mountain bikes ride the same
www.bikeradar.com www.bikeradar.com

study ground trail and mechanical trail, caster a horizontal force and wheel flop a vertical force. Longer trail is necessary on longer travel bikes to prevent a reverse in caster. Less wheel flop w reduced offset vs a slacker fork When trying to gain trail. Slacker forks much better on the transitions from steep to flat. Lots of good stuff in this article!

also consider what effects fork offset has w regard to effective stem length and hta. bar sweep changes your hand position over the steering axis and is affected by stem length. Stem length feels different when changing fork offset.

could we keep things consistent. Modify the fork travel a minor amount to maintain an identical hta, and adjust stem length to keep the same hand position over the front wheel. But this would affect hand sweep over the ht axis. we can try to isolate what a change in trail feels like.

too many things change just by bolting on a shorter or longer offset fork.

Imo. an expert rider will immediately notice the difference. However, they will also just ride around it.
 
Discussion starter · #19 ·
Bike in question is a Transition Spur. I was about to pull the trigger on the 51mm offset fork but I just found another deal which has 44mm offset for the same price and will likely go with that one.
 
#20 ·
Varaxis said:
I disagree. If you tried to simplify what I posted earlier, then I have to say that you did not comprehend it correctly. I simply stated that two sizes of the same bike can handle differently on the trail, and that was due to the front-center difference. I implied the fork offset could be one of the ways to tweak that FC difference, along with headsets that tweak reach or HA, as well as diff fork length.

You'd be closer to what I meant, if you said that bikes with too little rearward weight bias (excessively short FC) want more fork offset, and bikes with too much rearward weight bias (excessively long FC) want less. There's a very large number of XL/XXL bikes that have too little rearward weight bias and can use long offset (mostly short travel bikes). On rare occasion, some bikes have so much rearward bias that their small size can use short offset (e.g. Honzo ESD, Fuji Auric LT, latest Canyon Strive).

7mm of fork offset only offers a very small effect for people chasing very marginal gains. You'd have to have a fine understanding and fine tuned sense to feel like one offset option has a performance advantage over the other. The money savings is more than enough reason to go with one over the other.

IIRC, 51mm offset was originally brought to market through Gary Fisher G2 geometry, to make it so a 29er 100mm bike with 68° HA had a familiar/consistent steering feel compared to a smaller wheeled 100mm bike with 68° HA (with shorter offset fork).
Click to expand...
I wasn't simplifying what you wrote.
IMO XXL bike have a terrible weight balance. They always wash the front wheel and since manifactures are not building bikes with appropriately long chain stays you need far less offset. I currently run 36mm of offset on a 525 reach 63HTA bike. I wish I could run 20mm's of offset.

Small bikes tend to suffer from toe overlap and require extra wheel clearance in the form of offset. They also have too much front weight bias that increased offset helps mitigate.
 
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