USD forks?

I guess I should state exactly what I did, so as not to offend.

I put a ZX9R inverted front end on an '81 'J' and a ZX9R front end on an '82 GPz1100 and am in the process of putting an FZR1000 front end on my '78 Z1R. I guess I should have recorded the results as we (me and a couple friends at a motorcycle shop) weighed everything on scales when we made the swap. We were shocked, but we had a lot more stuff to be concerned about so I don't know if anyone even wrote down the differences. I'm guessing the weight difference is because of materials used and material wall thicknesses. When I do the Z1R I'll make sure to record the differences in the weights, component::component.

The handling results are night and day.

nice one guys, i'll be keeping my eyes open for second hand front ends on ebay, theres no hurry for now as i'm off to new zealand in about 2 weeks so will have to wait until i get back!

badkaw, what year ZX9's did you retrieve the usd front from?

I think they were USD from '94 - '97 or maybe '98(?). Anyway, they're 2.75" longer than ZX7R forks (which - outwardly - are very simlar in appearance). That extra length has been crutial for me in clearance issues.

-KR

does that raise the front end or do you lower it down by putting the forks further through the yokes?

iandz500 wrote:

does that raise the front end or do you lower it down by putting the forks further through the yokes?

No, actually with the 9 forks I left the top of the forks level with the top of the top triple clamp and it gives me plenty of ground clearance. So much so that my 'J' project has clip ons and I'm able to slide the tubes up enough to mount the clip-ons to the top of the triple clamp. I strongly suspect that it (the USD front end) lowers the front end just slightly; I am certain that the motorcycle itself has been lowered slightly. The stock 'J' rear wheel is an 18" with high bias-ply side-wall; the new wheel is a 17" with low-profile radial, so I suspect the rear to be riding closer to the ground as well.

On my first build (the 'J'...10yrs ago) the wrenches were flying and it happened so fast that I experienced the change to the suspension so fast that I was just extatic about how much better it was.

The Clone (ELR) suspension swap has gone a bit differently and it was only during the build that I even thought of taking before/after measurements ... and I didn't take the measurements b/c the massive improvement that occurred with the first build had no bad side effects ... I just figured it didn't matter.

My third build (I know: I have project-itis:blush: ) will be the Z1R during the spring/summer, swapping an FZR1000 front end and rear onto it. I WILL be taking measurements during this mod (to include ride height and the weight of individual components taken off and installed) ... that way I can give concrete data to those who doubt.

Post edited by: Bad Kaw, at: 2007/12/12 18:54

What about length? I think most sportbikes have forks 2 or 3 inches shorter than a KZ. Thus your front end rides lower and the rake is steeper.

This is because the KZ steering head is higher than most modern sportbikes.

And then- you put modern (longer) shocks on, which raises the back and steepens the rake even more. Seems like a twitchy ride to me...shopping cart handling?

I've got ZRX shocks on mine with stock front end. It's definitely quicker turning than it was with stock shocks.

Anyone?

Again: shame on me for not taking before/after measurements.

But: yes, the front is lowered a bit (how much?...:pinch: ) But, the rear is lowered also due to the 17" wheel being an inch smaller in diameter and the side-wall profile being so much smaller (lower) with a radial than on a bias ply that the rear seems to have been lowered at least as much as the front. Next time I'll take measurements FOR SURE, but as for the two bikes that I've done so far the handling is vastly improved...the stock set up doesn't compare.

-KR

I built mine with modern sport bike geometry in mind. The forks are 3" shorter, the rear was raised an additional 2" to get approx 25 to 26 degrees of rake. Because there is less offset in the modern USD triple clamps, there is enough trail even with the steep rake to maintain stability. Also, the shorter front end lowers the centre of gravity. The overall handling and control is like night and day - the bike went from a wallowing overweight, high centre of gravity underbraked evil/dangerous handling UJM to a quick handling, flickable but stable ride. Even if the geometry wasn't changed, the handling and control is improved with modern suspension. The modern wheels are 9 pounds lighter than stock also improving all aspects of handling and braking.

At LAST! Someone who was wise enough to take before measurements...as well as have goal measurements in mind...who'd o' thunk it!

Fossil, even if that bike is not in your garage now...you still da man! Always loved that ride...

Thanks Bad Kaw, I appreciate it. Post some pics of your projects as you go along, love to see them. Only wish I had documented my build.
People have posted in the past, they didn't understand why go to all that trouble, why not just buy a new bike? Anyone can buy a bike, there's much more satisfaction building and riding your own than plunking down the VISA card. The old air cooled carburated engines are advanced enough to make a lot of power and stay together, but primitive enough to have some character, to have that smell when you shut it off, clicking as it cools down. I refer to built up air cooled motors as "thermal-mechanical violence".
Those who understand, get it. At bike nights, some people asked what year it is and walk away. One night a guy on a Ducati Monster parked beside me and sat there looking at the GPZ for a minute. Asked, is that yours? Yep. Next thing out of his mouth was "holy sh!t".

I'm in the midst of deciding how far to go with my project bike. I thought I was gonna keep the suspension and wheels stock (except rear shocks), but maybe not.

I have a modern SV1000 that's light years faster and better handling. The KZ is more of a funky fun bike. but dangit the modern stuff sure handles better. tough decision - lots more work if I go for it.

Mark's got USD forks on his 650. Check with him as well on the conversion and specs. Not sure if he's been able to test ride her yet.