Benifits of USD forks?

[HDTboy]

Would an extra bush between the upper and lower ones fix it?

[TDC]

Would an extra bush between the upper and lower ones fix it?

Maybe from a rigidity perspective, but three bushes on a pair of disimilar tubes in a bending moment environment spells lots a stiction, so sadly no....

[HDTboy]

I should've known that

[TDC]

I should've known that

Don't beat yourself up! Most of the time I enjoy your questions, except for the one that require lotsa typing late at night

[HDTboy]

Is it late yet?

I understand that cartridge forks are better than damper rod forks, but I don't understand why. And where do I mount a fork oil reservoir on my bike?

[Pussy]

Is it late yet?

I understand that cartridge forks are better than damper rod forks, but I don't understand why. And where do I mount a fork oil reservoir on my bike?

You're a cruel bugger, Gav!!

[TDC]

You're a cruel bugger, Gav!!

No Puss he's a count!

[TDC]

You're a cruel bugger, Gav!!

Actually there is no 'o' in that is there.....

[JD Racing]

The USD fork has two bushes mounted at a fixed length of about 250mm apart in the upper tube, the lower bush is at the bottom of the upper tube and is quite poorly supported.

Not all USD Showa forks have fixed bushes, on most of their forks the upper bush is mounted on the stanchion so the bush moves up the slider as the forks compress. KYB, Soki and Ohlins use the fixed bush, Marzocchi use a sliding bush as do WP on the Roma fork.

[JD Racing]

Sort of but don't underestimate how much the freedom to put larger more capable cartridges has done to front end performance! For this reason alone the other trade offs are well worth it!

Has it never been possible to fit 25mm cartridges in conventional forks?????

[JD Racing]

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.....

Why is the oil flowing into the fork from the cartridge comparitively large compared to a USD fork, how much damping does this create, is it measurable on a dyno?

[JD Racing]

A negative of USD forks is that because of the bushing positions in the upper tubes ( one at the bottom of the upper tubes and one above the lower triple clamp ) they deflect off centre due to the tubes being distorted under braking loads or abrupt bump deflection. That causes friction so it is not all a bed of roses......

True, but all forks flex under braking and turning whether they are USD or conventional, it's not ideal from a stiction point of view but is a necessary evil for feel, if you made a set of forks that didn't flex at all nobody would like them.

[skidMark]

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

Pretty much.

[TDC]

Not all USD Showa forks have fixed bushes, on most of their forks the upper bush is mounted on the stanchion so the bush moves up the slider as the forks compress. KYB, Soki and Ohlins use the fixed bush, Marzocchi use a sliding bush as do WP on the Roma fork.

Agreed, it was the majority I was representing for the purposes of discussion.

[TDC]

Has it never been possible to fit 25mm cartridges in conventional forks?????

Technically yes but practically not so easy see next