Do you think your fork feels harsh over small bumps?
Chances are your fork lowers may have tight bushings, which is quite common! Especially on brand new forks.
I knew mines were not great ... I had to apply way too much force and wiggle the stanchions almost all the way to make the uppers slide into the lowers while servicing the fork. How could they be great at dampening small vibrations that don't generate enough force?? Once I realised that ... I ordered a tool to resize them.
Fork Bushing Sizing Tool
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Once received I measured the "head" on the tool to use with 35mm stanchions at 35.1mm.
![]()
Fox say correct bushing tolerance is a diametric clearance of
min: 0.0015" (0.0381 mm)
max: 0.0090" (0.2286 mm)
source: https://www.ridefox.com/fox_tech_center/owners_manuals/07/eng/bushing_technology_and_inspection.htm
That +0.1mm (0.003937") to resize/widen the bushings is perfect.
If you do the math and take Fox's recommandation to see what the result should be, you get:
(0.0090"-0.0015")/2 = 0,00375" (0.95mm)
Which is right in the middle!
RS doesn't even list the bushings on their "Spare Parts Catalog" because they are made to last forever (basically if the fork is well maintained, you won't have to worry about it), so I guess they make them a bit tighter now to backup that claim
Truth is, most of the time they are too tight and when people scratch their head and try to improve small bump compliance by tweaking x or y they miss the main culprit (tight bushings), it generates a ton of frictions and from there it's an uphill battle.
Do a test next time you service your fork.
1 - Drop the lowers
2 - Remove the damper/spring
3 - Remove the seals
4 - Cycle the uppers into the lowers by hand (with nothing else)
You'll be surprised (or shocked. LOL) by how much force you need to cycle the uppers ... I can almost guarantee they won't fall down like mine! If it's the case then your bushings are too tight/narrow.
![]()
Out of 3 forks I serviced recently (Pike/Lyrik/Yari), including my own they were all sticky and hard to cycle, you had to slightly move the uppers side to side to push them down ... and apply force at the same time!
Once I resized the bushings, well ... have a look at the gif, the uppers now drop under their own weigh into the lowers.
It's very easy to use the tool, just force it through the bushings with a twisting motion and you'll have perfectly honed out bushings in your fork. (apply some Motorex Supergliss on the head and on the bushings with a long paint brush before)
If you want to do it, you've got 3 options.
1) - Make it done by a proper suspension specialist/tuner (it's nice to do it when you need servicing or tuning)
2) - You could buy the Fox tool for about $1000, yeah you read that right (ref: 803-00-813), that includes all the diameters they make (32/34/36/40)
3) - Or you could ask Oliver at Blue Liquid Labs | An Oliver Majewski Project to make you one for 140USD with any head diameter you want/need (that's what I did)
And don't forget to lube them with a nice slippery oil such as the Motorex Supergliss 100k (Big thanks to Dougal for testing and releasing that info)
![]()
Resizing your bushes will give you slick, super smooth, stiction free action ... IMO that's the number 1 thing to verify and correct if necessary before modifying anything else. You can definitely feel the difference over small bumps and chatter it's incredibly supple off the top now.
because the fork doesn't need a lot of force to start moving/reacting and make those stanchions slide (they are not micro-stuck like before). it's a bit like when you have seized bearings on your frame, because of the weight/leverage AND it probably happened over a long period of time you can't really tell ... until you swap them for fresh ones and all of a sudden it feels like a brand new bike and your shock can do it's job to dampen small vibrations and chatter, NOW you can feel it ... well it's the same feel
I hope it will be helpful for some of you!
Some comments about tight bushings ...
TF-TUNED (MTB suspension tuners in the UK) say:
Fox about Race Prepping a Fox 40
Chances are your fork lowers may have tight bushings, which is quite common! Especially on brand new forks.
I knew mines were not great ... I had to apply way too much force and wiggle the stanchions almost all the way to make the uppers slide into the lowers while servicing the fork. How could they be great at dampening small vibrations that don't generate enough force?? Once I realised that ... I ordered a tool to resize them.
Fork Bushing Sizing Tool
Once received I measured the "head" on the tool to use with 35mm stanchions at 35.1mm.
Fox say correct bushing tolerance is a diametric clearance of
min: 0.0015" (0.0381 mm)
max: 0.0090" (0.2286 mm)
source: https://www.ridefox.com/fox_tech_center/owners_manuals/07/eng/bushing_technology_and_inspection.htm
That +0.1mm (0.003937") to resize/widen the bushings is perfect.
If you do the math and take Fox's recommandation to see what the result should be, you get:
(0.0090"-0.0015")/2 = 0,00375" (0.95mm)
Which is right in the middle!
RS doesn't even list the bushings on their "Spare Parts Catalog" because they are made to last forever (basically if the fork is well maintained, you won't have to worry about it), so I guess they make them a bit tighter now to backup that claim
Truth is, most of the time they are too tight and when people scratch their head and try to improve small bump compliance by tweaking x or y they miss the main culprit (tight bushings), it generates a ton of frictions and from there it's an uphill battle.
Do a test next time you service your fork.
1 - Drop the lowers
2 - Remove the damper/spring
3 - Remove the seals
4 - Cycle the uppers into the lowers by hand (with nothing else)
You'll be surprised (or shocked. LOL) by how much force you need to cycle the uppers ... I can almost guarantee they won't fall down like mine! If it's the case then your bushings are too tight/narrow.
Out of 3 forks I serviced recently (Pike/Lyrik/Yari), including my own they were all sticky and hard to cycle, you had to slightly move the uppers side to side to push them down ... and apply force at the same time!
Once I resized the bushings, well ... have a look at the gif, the uppers now drop under their own weigh into the lowers.
It's very easy to use the tool, just force it through the bushings with a twisting motion and you'll have perfectly honed out bushings in your fork. (apply some Motorex Supergliss on the head and on the bushings with a long paint brush before)
If you want to do it, you've got 3 options.
1) - Make it done by a proper suspension specialist/tuner (it's nice to do it when you need servicing or tuning)
2) - You could buy the Fox tool for about $1000, yeah you read that right (ref: 803-00-813), that includes all the diameters they make (32/34/36/40)
3) - Or you could ask Oliver at Blue Liquid Labs | An Oliver Majewski Project to make you one for 140USD with any head diameter you want/need (that's what I did)
And don't forget to lube them with a nice slippery oil such as the Motorex Supergliss 100k (Big thanks to Dougal for testing and releasing that info)
Resizing your bushes will give you slick, super smooth, stiction free action ... IMO that's the number 1 thing to verify and correct if necessary before modifying anything else. You can definitely feel the difference over small bumps and chatter it's incredibly supple off the top now.
because the fork doesn't need a lot of force to start moving/reacting and make those stanchions slide (they are not micro-stuck like before). it's a bit like when you have seized bearings on your frame, because of the weight/leverage AND it probably happened over a long period of time you can't really tell ... until you swap them for fresh ones and all of a sudden it feels like a brand new bike and your shock can do it's job to dampen small vibrations and chatter, NOW you can feel it ... well it's the same feel
I hope it will be helpful for some of you!
Some comments about tight bushings ...
TF-TUNED (MTB suspension tuners in the UK) say:
source: https://www.tftuned.com/tech-help/22-rockshox
Fox about Race Prepping a Fox 40
Source: https://www.pinkbike.com/news/race-prepping-a-fox-40.html
