Benifits of USD forks?

[Sir_hoppalot]

My new bike has them, don't think they are standard with the model but interested in the advantages/disadvantages of them.

[Gubb]

skidMark is the resident expert on USD Forks.

If he can't answer your question, there *is* no answer.

[Winter]

My new bike has them, don't think they are standard with the model but interested in the advantages/disadvantages of them.

In amongst all this USD hilarity - I'm not certain i know the true advantages either.

I always guessed it was to help keep road spooge off the forks - to help improve fork seal life?

I wouldn't mind a sensible, honest answer to this question.
Dont know why I'm asking here then!

[bane]

my (admittedly uninformed) opinion is USD forks reduce unsprung weight and probably something else important....

[GSVR]

I think Rigidity is the major gain. But someone like Robert Taylor will have accurate info on the subject.

You could always type a few searches into Google like USD + Advantages + Forks

[Drum]

My understanding was that they are more rigid and therefore less deformation under heavy braking. Never had them tho, so shouldn't really comment.

[GSVR]

http://en.wikipedia.org/wiki/Motorcycle_fork

[Skunk]

Cheers Garry.

On many sport bikes, this system is inverted, with the spring/damper unit clamped to the yoke while the sliders are at the bottom of the assembly. This is done for two reasons: to reduce unsprung weight by having the heavier components be suspended, and to improve the strength and rigidity of the assembly by having the bulkier and stronger component being directly supported by the pivot. Such a system is referred to by many as upside-down forks or USD for short.

[R6_kid:Me]

skidmarks answer: the zxr has them and the cbr doesnt, hondas are gay therefore USD for the win.

[TDC]

My new bike has them, don't think they are standard with the model but interested in the advantages/disadvantages of them.

The whole USD fork question is quite interesting. They are probably not quite as rigid (bending wise) as a conventional fork size for size and as a result tend to bigger in diameter (and as a result more rigid). More difficult to mount brakes on. The unsprung weight in some instances can be a little lighter, but only due to quality of design / materials. The clamping area on the triple clamps is much improved which tends to improve the resistance to a head shake twisting the front end out of alignment. The real benefit is when fitted a cartridge damper it does not suffer the same undesirable critical flow problems that conventional forks do when fitted with a cartridge damper. Simply the oil on the bottom of a conventional fork has to pass between the cartridge and the fork tube in the conventional design in comparatively large volumes, this imparts undesirable damping "artifacts" in to the action of the fork and limits the maximum size of the cartridge that can be fitted for a given fork tube diameter. The USD fork does not have these problems and as such was used in racing, them became fashionable, now its probably more expensive to make a conventional fork due to the numbers game.....

[Cruisin' Craig]

The next question that occured to me was: why do we necessarily want to reduce the unsprung weight?

I found that this wikipedia article explaned the reasons very well.

http://en.wikipedia.org/wiki/Unsprung_weight

[Fastchick]

they look cool

[Cruisin' Craig]

..... They are probably not quite as rigid (bending wise) as a conventional fork size for size and as a result tend to bigger in diameter (and as a result more rigid). More difficult to mount brakes on.

Can you explain why they would be less rigid for the same diameter? Personally I don't understand why there would be a difference either way

The unsprung weight in some instances can be a little lighter, but only due to quality of design / materials.....

Also, I think the reason the unsprung weight is reduced is because the oil reservoir is shifted above the triple clamp and has hence become part of the sprung weight. So I don't think it's just to do with materials.

[HDTboy]

Also, I think the reason the unsprung weight is reduced is because the oil reservoir is shifted above the triple clamp and has hence become part of the sprung weight. So I don't think it's just to do with materials.

Oil reservoir? Please explain.

[Cruisin' Craig]

Oil reservoir? Please explain.

I mean that with UPS forks the part where all the damping oil is stored is up top above the clamp instead of down the bottom where it would otherwise contribut to the unsprung weight.