link1896
Mr Greenfield
Another fun area I’ve been playing with is fork bushings. Fork bushings are a critical part of forks that all too often get neglected until they have worn through the stanchions coating.
Bushings are the contact points between the uppers and lowers, that the stanchions slide on.
Many many forks fresh from the factory, regardless of brand or model, have a poor bushing fit. Too tight and the fork will feel harsh , too loose and when you apply the brakes the front axle chatters.
Bushings need to fit the stanchions just right. Enough clearance so the stanchion slides with a layer of oil between it and the bushing. We’ve all seen what a fork that’s run dry looks like, with hideous gouge marks on the stanchions.
Here’s what Fox bushings look like out of the fork. A PTFE layer ontop a steel band. Notice the taller bushings have slots for oil to migrate. Also notice how the steel band has a slot. This slot is to allow the bushing to locate into the lowers properly. This shape of the bushing is what caused them to bind, which causes harshness. Invariably, the steel band isn’t actually round, but egg shaped. At the factory assembly stage, they are hoping the insertion of the uppers forces the bushing to take a round shape. Often not the case.
Fox has tools available, at eye watering prices, >1000 aud. The burnishing tool, for setting shape and bushing diameter, is simply a round, smooth lump of steel on the end of a rod, with chamfered edges, at a critical diameter. Again Oliver Majewaki started making the burnishing tool with exchangeable heads a few years ago. Fox, and others also makes a tool for removing and setting bushings. Fox sells replacement bushings, RS does not. A bunch of after market bushings have started to appear, along with after market stanchions. It should be pointed out, once a stanchion has had its coating worn through, the bushings are toast, as they have now been impregnated with the anodize and raw aluminium, and will trash new stanchions rapidly.
Getting bushing fit sorted is well worth it. Drop the fork internals out (air spring, damper) and remove wipers. You need the wheel installed, so the lowers are clamped at the correct width. (I’ve made an adjustable tool for setting lowers width to the nominal widths for checking when I don’t have the wheel). Uppers should slide into the lowers with nothing more then gravity or a very slight nudge when dry. But conversely, putting one stanchion into the bushings at a time, one has to check for excess play for gaps too wide.
If the uppers and lowers bind when the wheels is in and the thru axle is done up, hub width is questionable, or dropouts haven’t been machined properly.
There is more to it, but essentially this is an area of fork performance that hasn’t been given enough attention.
Bushings are the contact points between the uppers and lowers, that the stanchions slide on.
Many many forks fresh from the factory, regardless of brand or model, have a poor bushing fit. Too tight and the fork will feel harsh , too loose and when you apply the brakes the front axle chatters.
Bushings need to fit the stanchions just right. Enough clearance so the stanchion slides with a layer of oil between it and the bushing. We’ve all seen what a fork that’s run dry looks like, with hideous gouge marks on the stanchions.
Here’s what Fox bushings look like out of the fork. A PTFE layer ontop a steel band. Notice the taller bushings have slots for oil to migrate. Also notice how the steel band has a slot. This slot is to allow the bushing to locate into the lowers properly. This shape of the bushing is what caused them to bind, which causes harshness. Invariably, the steel band isn’t actually round, but egg shaped. At the factory assembly stage, they are hoping the insertion of the uppers forces the bushing to take a round shape. Often not the case.
Fox has tools available, at eye watering prices, >1000 aud. The burnishing tool, for setting shape and bushing diameter, is simply a round, smooth lump of steel on the end of a rod, with chamfered edges, at a critical diameter. Again Oliver Majewaki started making the burnishing tool with exchangeable heads a few years ago. Fox, and others also makes a tool for removing and setting bushings. Fox sells replacement bushings, RS does not. A bunch of after market bushings have started to appear, along with after market stanchions. It should be pointed out, once a stanchion has had its coating worn through, the bushings are toast, as they have now been impregnated with the anodize and raw aluminium, and will trash new stanchions rapidly.
Getting bushing fit sorted is well worth it. Drop the fork internals out (air spring, damper) and remove wipers. You need the wheel installed, so the lowers are clamped at the correct width. (I’ve made an adjustable tool for setting lowers width to the nominal widths for checking when I don’t have the wheel). Uppers should slide into the lowers with nothing more then gravity or a very slight nudge when dry. But conversely, putting one stanchion into the bushings at a time, one has to check for excess play for gaps too wide.
If the uppers and lowers bind when the wheels is in and the thru axle is done up, hub width is questionable, or dropouts haven’t been machined properly.
There is more to it, but essentially this is an area of fork performance that hasn’t been given enough attention.
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Similar to what you suggest, there's a lot at play so it could be a combination of minor things. Luckily through sheer serendipity it's working great as is - so I'm not planning to mess with it!