Benifits of USD forks?

[SixPackBack]

I was going to say that a roller bearing would only touch at one point and make it vunerable to damaging the stanchion, but I suppose you could use a curved one like boats use, but once you have your magnificent $300 worth of bearings you have added a kilo of weight, made the fork outers cost $10,000 to build (needs to contain the bearings with very little excess space, created a large pool for fluid to circulate through AND you now have the play in the bearings, no matter how infitesimally small to deal with, hmm, I think I'll be searching for lower friction bushes :P

The only real issue from those mentioned is high point loading through single point contact. Cost, design, weight and space utilisation are relativley easily overcome. Also play in bearings in theory could be smaller than a linear bush.

[Ocean1]

Stiction is obviously an issue and so why do manufactures not utilise linear roller bearings? this would completely eliminate stiction.

At a guess I'd say cost and the fork tube still needs to bend a little otherwise you lose feel.

I was going to say that a roller bearing would only touch at one point and make it vunerable to damaging the stanchion, but I suppose you could use a curved one like boats use, but once you have your magnificent $300 worth of bearings you have added a kilo of weight, made the fork outers cost $10,000 to build (needs to contain the bearings with very little excess space, created a large pool for fluid to circulate through AND you now have the play in the bearings, no matter how infitesimally small to deal with, hmm, I think I'll be searching for lower friction bushes :P

For general engineering considerations the types of linear bearing that can work with a cylindrical shaft do place a hugh point contact load on the shaft surface. The bearings themselves aren't that much heavier than a conventional bush but the shafts tend to be large, solid or very heavy wall, hardened and prone to damage. You can get reciprocating ball bearings that run in a grooved or non-cylindrical shafts, but then you've got seal issues.

There's some new bearing materials that may be quite good for such applications, scintered ceramics is one.

I'm not sure what would feel different if there was zero flex, or if that difference would be beneficial or detrimental to handling. I'm guessing eliminating an uncontroled lateral variable would be a good thing, same with less stiction.

These problems are much less evident with leading/trailing arm arangements, which can have a wonderful lack of initial friction, it's just that there's structural issues there too.

[JD Racing]

I didn't say the oil flowing from the cartridge is any different on either solution.

The lower slider on a conventional fork is largely full of oil that is displaced by the entry of the upper tube when the fork compresses, this very thing thing is what a damper rod fork relies on to work. However when you put a cartridge in there unless you have a lot of clearance round the cartridge and inside wall of the upper tube the large volume that has to make it way in and out of the lower tube via the upper tube has to squeeze past the cartridge. If this space becomes even slightly restrictive the dyno will show it.

Having done the calculation I can assure you that the cartridge top generates absolutely zero damping.