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29er Fork Offset! Lets Talk!

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sb1616ne

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Discussion starter · #1 ·
I am curious to see what people think who have ridden 29ers with different fork offsets. Some frame manufactures seem to be all over the place when is comes to fork offset, most of the longer travel enduro focused bikes that have been launched recently however seem to be low offset. Here is a a short list:

Yeti SB100, 130, and 150--44mm
Pivot Firebird 29--44mm
Pivot 429 Trail--51mm
Intense Sniper--44mm(100mm fork), 51mm(120mm fork)
YT Capra 29--51mm
Mondraker Foxy 29--44mm
Giant Trance 29--44mm
Specialized Epic Evo--44mm
Orbea Rallon
Santa Cruz Blur--44mm


I am currently riding two bikes and I can't seem to jive with the front end feel of either. I have a 2017 Kona Hei Hei 29 DL that I have both a Fox 32 SC 100mm and Fox 34 130mm Grip(both 51mm offset. The Kona does have a steeper HT angle than some of the really aggressive short travel bikes like the Sniper. My other ride is an Evil Wreckoning that I built up around a 160mm Fox 36 with the 44mm offset.

As an engineer who like to tinker I am going to do some back to back testing with different offsets. I scored a deal on the same 36 I run just with a 51mm offset. I also bought a -1 angle set for this bike.

This winter I hope to do the same with the Hei Hei and see how it rides with an angle set and 44mm 34. Just waiting for a deal on a used fork.

Will 44mm be the standard across the board even for xc 29ers?
 
#2 ·
I also have a Hei Hei DL with a 120mm fork and agree it's pretty twitchy for a bike with a 68 HTA. Not that it's necessarily a bad thing as that's what it's designed to do (endurance XC race bike) but I am also curious about a 44 offset fork vs an angle set and perhaps extending it to 130mm.

While there are some general rules that apply, it's tough to make a direct comparison of two very different bikes as there are many factors that influence how a bike handles. Aside from the things that you already mentioned like HTA and fork offset, the wheelbase, BB drop, stem length/handlebar width, chainstay length, front center, etc can all influence the way a bike feels.

It will be much more accurate info to test different setups on the same bike. Curious to hear your impression after you spend some time on the different setups.
 
#4 ·
I think, at this point, every 29er coming out in the next year or two will be using reduced offset forks and the "SBG" treatment. There are a few others not on your list, as well (Smuggler, Sentinel, Ripmo, Stumpjumper EVO).

It doesn't seem to have taken off with 27.5 (outside of Transition's lineup) for some reason, but I wonder if the benefits to the smaller wheel size are more negligible?

At any rate, it's hard to weigh the change unless you've run the exact same bike with the same fork just with different offsets. Most of the bikes you list had considerable other geometry changes made (longer, slacker, etc), so weighing them against their previous versions or counterparts isn't going to work.

I haven't had the chance to experiment because my only option would be to use different fork models and I'm not sure that's a good comparison. My understanding from folks that have is that the reduced offset forks make the bike feel shorter (in terms of turning, less monstertruck feel even with a longer reach), corner better at speed, and seem to stay more stable through technical terrain.

I think if your problem with the cornering of your other bikes is that it feels slow turning or unresponsive, reducing offset may help with that. If it feels twitchy, then reducing offset would make it worse.
 
#5 ·
I believe if the fork is 27.5 it's already using the shorter offset. 27.5/29 forks use 51mm offset. When you modify an older 29 fork you're using a 27.5 CSU. My buddy did this to his older Pike using a 40mm offset CSU for a 27.5 fork.
I also believe that slackening the head angle helps to reduce the twitchy feeling you would get with the shorter offset.
 
#6 ·
I had a 51mm offset 150mm 34 on my HT and switched to a 42mm offset 140mm Lyrik. The one thing that was very noticeable was the front wheel gripping better in corners. The bike felt slightly different but that feeling went away in a few minutes. Not night and day, but enough change for me to feel.
 
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#8 ·
I have experimented with three different forks on my 27.5 bike, each with different offsets. One fork had 37mm, one had 41mm, and one had 51mm. I preferred the 41mm offset on my 27.5, and would probably prefer the 51mm on a 29er, but it depends on the bike geometry as well.

Reduced offset means longer mechanical trail. In my experience, longer trail figures require more body english to steer the bike. It feels like you have to lean the bike to steer more than turn the handlebars, and it feels very stable.

More offset results in shorter trail figures. This makes the steering feel more twitchy and snappy, but also less stable.

Ultimately it comes down to matching the fork offset to the frame geometry (i.e. head angle, and front center length) to get the right trail numbers. I found that a trail numbers between 100mm to 125mm to be ideal, which coincidentally is what most motocross bikes are running.

I think the latest trend of super slack head angles AND less offset is a step in the wrong direction, making bikes too lethargic and ungainly. IMO slacker bikes need MORE offset, and steeper bikes need LESS offset to maintain the proper trail figures.
 
#9 ·
Yokozuna said:
I think the latest trend of super slack head angles AND less offset is a step in the wrong direction, making bikes too lethargic and ungainly. IMO slacker bikes need MORE offset, and steeper bikes need LESS offset to maintain the proper trail figures.
Click to expand...
This is not my experience on my HT with a 65.5° HTA.
 
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#10 ·
Having now ridden and compared a couple 27.5" and 29" forks for a longer period of time, I have a few observations. The bottom line is that I have really drunk the Kool-aid on Transition's SBG setup and their application of short offset forks. Here are my observations / opinions:

Shorter Offset increases trail just like a slacker head angle does BUT it does not have exactly the same effect on handling, especially at low speed because it also reduces the torque / force / lever arm applied to the handle bars around the steering axis. What that means is that you get all the same things that more trail normally causes like high speed stability and more wheel flop (which means it is easier to turn using weight shifts rather than just turning the bars). However, it also takes less force to turn the wheel or keep it straight, especially as slower speeds. This is why one of the ingredients of Transition's SBG setup is a very slack head angle to start with. If your head angle is not slack enough and you put a short offset fork on the bike, it can feel twitchy, especially at low speeds.

One huge advantage of this reduced leverage caused by the reduced offset is that when you have a slack head angle it is still very easy to control the front wheel on very steep and slow technical terrain. Have you ever had your front wheel flop to full lock because you applied the front brakes while trying to turn on a steep, descending, rocky corner? Reduced offset means that it takes much less force to control the wheel flop in this kind of situation, making these sorts of maneuvers much less sketchy feeling. On the flip side, at high speed this reduced leverage also makes it easier to control front wheel deflection due to hitting roots and rocks, and it still allows you to overcome the inherent stability caused by the larger amount of trail when you do need to turn.

While some people may not like the feel of the reduced offset, and it may not work well on a bike that has a head angle steeper than 65 degrees, I think it is the ideal setup for an all mountain / enduro bike in the Pacific North West, both for steep, slow tech and high speed bike park riding.
 
Discussion starter · #11 ·
This is all very interesting stuff. What has promoted me to buy another fork for the Weckoning was the way it feels in mid to slow speed tech. For the two prior years I rode a Following with an 130mm 51mm fork. This bike would feel good on everything from rock hopping to high speed berms.

Last winter where I demoed a Wreckoning in Sedona for 3 long days in the saddle. I got use to this bike with the 51mm offset longer travel fork right away. I was picking away at techy lines like it was my own bike right away. After reading all about the new longer travel 29ers this winter/spring with 44mm forks I figured I would try one out and Fox was selling them already. After logging about 1000 miles on this bike I still can;t get use to the steering response at slower speeds. I have ridden a friends SBG Sentinel and I really struggled with this as slower speeds also. I just worked up some trail numbers of my bikes:

Hei Hei 29 51mm 130mm -- 99mm
Following V1 51mm 130mm -- 102mm
Wreckoning 51mm 160mm -- 112mm
Wreckoning 44mm 160mm -- 119mm
Friends SBG Sentinel 44mm 160mm -- 133mm

I live in the northeast where midweek we ride pretty much 100% XC trails mid week and then shuttles and lift laps on the weekends. The last DH bike I owned was a 2015 GT fury 26". The slow speed steering of this bike felt better than my Wreckoning and when looking at just the trail number of 116mm for this bike it makes sense.

I have been riding for 15 years and I feel like the manufactures are so focused with making the average joe(including myself here) feel like they can take enduro bike to DH speeds that the trial bikes have lost there fun snap. Fork offset, super long TT's, and slack HTA's are good to a point, but I feel we have reached a point where the bikes don't need any of this.

I am going to spend some real time swapping between the 44mm and 51mm and report back. The 44mm does make the bike feel "calmer" however these modern 29ers with a 1000 plus gram euduro tire are all ready point and shoot monsters.
 
Discussion starter · #13 ·
I just stumbled across this exact topic discussing the fork offset of the Wreckoning.

http://forums.mtbr.com/evil-bikes/wreckoning-170mm-44-offset-fork-1083863.html

This comment is exactly how I feel the bike rides with the 44mm fork:

"I've got a couple more rides with the short offset fork and noticed some of the draw backs. In slow tech I was having to fight understeer a lot more and noticed the front wheel gets knocked off line a lot easier. This is a pretty negative cuz getting bumped around on a techy part of the trail when your friend momentum is gone is an easy way to lay her over. But when you're rolling the short offset initiates turns with a lot more ease and control."
 
#14 ·
Xorrox said:
If your head angle is not slack enough and you put a short offset fork on the bike, it can feel twitchy, especially at low speeds.

While some people may not like the feel of the reduced offset, and it may not work well on a bike that has a head angle steeper than 65 degrees, I think it is the ideal setup for an all mountain / enduro bike in the Pacific North West, both for steep, slow tech and high speed bike park riding.
Click to expand...
My old 2011 Kona Unit (old school XC geo) used a 44mm offset rigid fork with a 71.5 degree HTA.

There's more to it than simply stating X is for enduro bikes and Y is for trail bikes.
 
#15 · (Edited)
sb1616ne said:
I am curious to see what people think who have ridden 29ers with different fork offsets. Some frame manufactures seem to be all over the place when is comes to fork offset, most of the longer travel enduro focused bikes that have been launched recently however seem to be low offset. Here is a a short list:

Yeti SB100, 130, and 150--44mm
Pivot Firebird 29--44mm
Pivot 429 Trail--51mm
Intense Sniper--44mm(100mm fork), 51mm(120mm fork)
YT Capra 29--51mm
Mondraker Foxy 29--44mm
Giant Trance 29--44mm
Specialized Epic Evo--44mm
Orbea Rallon
Santa Cruz Blur--44mm

I am currently riding two bikes and I can't seem to jive with the front end feel of either. I have a 2017 Kona Hei Hei 29 DL that I have both a Fox 32 SC 100mm and Fox 34 130mm Grip(both 51mm offset. The Kona does have a steeper HT angle than some of the really aggressive short travel bikes like the Sniper. My other ride is an Evil Wreckoning that I built up around a 160mm Fox 36 with the 44mm offset.

As an engineer who like to tinker I am going to do some back to back testing with different offsets. I scored a deal on the same 36 I run just with a 51mm offset. I also bought a -1 angle set for this bike.

This winter I hope to do the same with the Hei Hei and see how it rides with an angle set and 44mm 34. Just waiting for a deal on a used fork.

Will 44mm be the standard across the board even for xc 29ers?
Click to expand...
*OneSpeed* said:
I also have a Hei Hei DL with a 120mm fork and agree it's pretty twitchy for a bike with a 68 HTA. Not that it's necessarily a bad thing as that's what it's designed to do (endurance XC race bike) but I am also curious about a 44 offset fork vs an angle set and perhaps extending it to 130mm.

While there are some general rules that apply, it's tough to make a direct comparison of two very different bikes as there are many factors that influence how a bike handles. Aside from the things that you already mentioned like HTA and fork offset, the wheelbase, BB drop, stem length/handlebar width, chainstay length, front center, etc can all influence the way a bike feels.

It will be much more accurate info to test different setups on the same bike. Curious to hear your impression after you spend some time on the different setups.
Click to expand...
Currently building a 2018 HEI HEI 29 carbon and installing a 2* works headset and 120mm pike with 40mm CSU from a 26". I ran this combo on my process 111 but at 130mm and liked how it smoothed out the bike and it needed less steering corrections in turns. Fast and slow speeds.

I'll post my results when I finish the build.
 
#17 ·
I really believe it's a good idea to pay attention to mechanical trail numbers when it comes to fork offset if you're deviating from the frame manufactures intended design. SBG is Transitions geometry package that uses the 44mm shorter offset to work with their complete bike geometry. Just modifying one aspect of geometry like fork offset can have strange feeling results taken out of context.

I use this trail calculator a fair bit to confirm geometry and trail. http://www.yojimg.net/bike/web_tools/trailcalc.php.

I have a v1 Evil The Following that I swap forks and wheels on. I originally built it with a 140mm Stage, then added a 120mm RS-1 for a couple reasons. Then I swapped in a -1 deg Works headset on the bike and run it almost exclusively in the higher geo to maintain a steeper SA. The Stage is a 51mm offset and I like the handling and mech trail that results from that setup. I bought a 46mm offset RS-1 and confirmed that the trail numbers would be similar to the longer Stage with the 51 OS. There is a 1mm delta in trail between them so the bike feels and handles very similar with both forks and I can compensate with spacers under the stem for the stack delta.
 
#18 ·
manitou2200 said:
I really believe it's a good idea to pay attention to mechanical trail numbers when it comes to fork offset if you're deviating from the frame manufactures intended design. SBG is Transitions geometry package that uses the 44mm shorter offset to work with their complete bike geometry. Just modifying one aspect of geometry like fork offset can have strange feeling results taken out of context.

I use this trail calculator a fair bit to confirm geometry and trail. http://www.yojimg.net/bike/web_tools/trailcalc.php.

I have a v1 Evil The Following that I swap forks and wheels on. I originally built it with a 140mm Stage, then added a 120mm RS-1 for a couple reasons. Then I swapped in a -1 deg Works headset on the bike and run it almost exclusively in the higher geo to maintain a steeper SA. The Stage is a 51mm offset and I like the handling and mech trail that results from that setup. I bought a 46mm offset RS-1 and confirmed that the trail numbers would be similar to the longer Stage with the 51 OS. There is a 1mm delta in trail between them so the bike feels and handles very similar with both forks and I can compensate with spacers under the stem for the stack delta.
Click to expand...
I have used that calculator as well. Say you switch not only offset, but also length. Head angle change too so that must be taken into account too.

Sent from my SM-G955U using Tapatalk
 
#19 · (Edited)
I wouldn't over think this too much. SBG is not magic. Transition just slacked the hta and shortened the CSU offset. The reach, sta and stack are similar to many other bikes with 51mm forks.

I also built a sentinel the same time I did the swap on my process 111 so it was easy to compare.

We can all admit results are subjective.
 
#20 ·
bogeydog said:
I have used that calculator as well. Say you switch not only offset, but also length. Head angle change too so that must be taken into account too.

Sent from my SM-G955U using Tapatalk
Click to expand...
Exactly.

It's kind of funny that these shorter offsets are all the rage now. But you need to keep all of it in context or you're just screwing around and maybe you'll get lucky with a configuration.
 
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