USD vs Conventional Forks

redzedx7r · Post by **redzedx7r** » Fri Jun 09, 2006 10:49 pm

Hey you moto tech geeks can someone 'please explain' the benefit or diadvantages of each. Manufacturers advertise that their sports bikes are fitted with USD's but still produce sport tourers and nakeds with conventional forks..why is it so?

Felix · Post by **Felix** » Fri Jun 09, 2006 11:28 pm

USD's are stiffer - less flex = better handling & control...Oh and lesser unsprung weight too, I think...

Dunno really, but I suspect "normal" forks must be cheaper. I suspect that if it made enough difference, then they'd all be USD's. But obviously it is only sports machines where it really matters.

I do know that one of the yammy cruisers uses USD's, but that is really to keep costs down - they needed big brakes, so they basically just used R1 forks as a complete unit, maybe tuned differently, but no need to develop the whole thing from scratch.

RG · Post by RG » Sat Jun 10, 2006 12:01 am

Including those Felix had mentioned, my guess is that it's got something to do with impact protection. It's abit of 'handling in corners' vs 'impact n cost of replacement'.

A general example, a CBR1000 vs a ST1300.
If both were to have a same low speed(eg: 50km/h) collision with a car, chances are that the CBR rider will be thrown very far forward and the ST rider might not be thrown very far(or not even thrown forward at all).
The conventional forks on the ST might have absorbed the impact and thus destroying itself in the process. Cost: replace fork n cosmetic damages.
The inverted forks on the CBR is stiffer n heavier, upon such low-speed impact, it might not give way, force is transferred to the bike frame, and thus the rider is thrown forward (due to riding position too). Cost: replace bike.

(Note: We are considering a low-speed collision. Everything will fly in a high speed crash.)

I guess that's the reason why we see heaps of write-off for these big sports bike. They are made to handle well but not crash well.

That's only my theory, not meant to be an arguement. It most probably won't make any sense to most ppl.

Cheers

photomike666 · Post by **photomike666** » Sat Jun 10, 2006 11:39 am

I think it's down to stiffness (or flexibility) Vs cost.

Both types have an internal stansion (sp) that runs the whole lenght of the fork, they also have a large strut that holds all the internal workings.

With conventional forks the leg is fairly short, and lots of stansion sticks out the top. A thin chrome tube is a lot cheaper than the leg part, but has more flex.

With USD forks the leg (now upper) is much longer, and thus stiffer - but much more expensive. Having a larger leg also increases the amount of iol and thus improves damping ability.

Note that the stansion will be the same lenght in both types, but the leg length will differ. It is also worth noting that the USD forks require much larger tripple clamps.

FrogZ · Post by **FrogZ** » Wed Jun 14, 2006 9:45 am

What everyone else said PLUS

....MARKETING....

you KNOW you NEED titinium nitrided USD's....

mike-s · Post by **mike-s** » Wed Jun 14, 2006 12:56 pm

titanium nitrided us Dollars? yes please, as long as its worth a lot more than a normal USD!

Stace · Post by **Stace** » Wed Jun 14, 2006 1:05 pm

frogzx12r wrote:What everyone else said PLUS

....MARKETING....

you KNOW you NEED titinium nitrided USD's....

titinium nitriding is basicially just a coating on the outside of the fork slider. All it does is provide a smoother, slicker surface for the seals to slide over, thus reducing stiction and improving the performance of the fork. The factory bikes in road racing, motocross and trials have been using it for years in different forms.

Smitty · Post by **Smitty** » Wed Jun 14, 2006 1:45 pm

Stace wrote: titinium nitriding is basicially just a coating on the outside of the fork slider. All it does is provide a smoother, slicker surface for the seals to slide over, thus reducing stiction and improving the performance of the fork. The factory bikes in road racing, motocross and trials have been using it for years in different forms.

aaah..tis a luvverly word 'stiction'

for those who don't know it means
sticky friction

or in other words...
unsmooth sliding (and thats bad english

)

Maty10 · Post by **Maty10** » Thu Jun 15, 2006 7:04 pm

Smitty wrote: or in other words...
unsmooth sliding (and thats bad english )

Not really. Stiction is the force that opposes an object from BEGINNING to move, key word beginning.

Friction is the force created as two objects slide against each other.

Stiction, usually, is a much stronger force to overcome than friction.

photomike666 · Post by **photomike666** » Fri Jun 16, 2006 12:47 am

So stiction is the laymans terms for the coefficient of friction - the force required to break friction.

Strika · Post by **Strika** » Fri Jun 16, 2006 7:41 am

photomike666 wrote:So stiction is the laymans terms for the coefficient of friction - the force required to break friction.

No Milke! Friction is the force created by two objects sliding across each other. Stiction is a measurement of how much force is required to commence the movement! HTH

So In other words, stiction is how big the bump needs to be to overcome the grip that that inner fork tube has over the outer fork tube to get it to initially move.

photomike666 · Post by **photomike666** » Fri Jun 16, 2006 9:52 am

Strika wrote:
photomike666 wrote:So stiction is the laymans terms for the coefficient of friction - the force required to break friction.
No Milke! Friction is the force created by two objects sliding across each other. Stiction is a measurement of how much force is required to commence the movement! HTH

So In other words, stiction is how big the bump needs to be to overcome the grip that that inner fork tube has over the outer fork tube to get it to initially move.

OK, coz the coefficient of friction is a measure of grip. If you're cornering the friction is holding you from sliding out, once you reach a certain piont the the friction will no longer hold the force and you slide - you have passed the coefficient (or maximum load) of friction.