Lonnie"s suggestion of Progressive suspension is spot on!
You might, however, go ahead and try adding spacers to the front to stiffen it up. Cheap experiment which may give good results.
Remember if you have a lot of sag in the front and take it out with spacers or stiffer springs you might change the rake and trail back to what it was before or even more, reversing the gains you've made with your shimmy and steering effort.
If stiffening your forks results in the shimmy coming back or increased steering effort, look at your rear suspension too. Stiffen or jack up the rear so you you keep the steepened rake. you can use stiffer springs and heavy shocks to reduce sag. If you have room you may be able to use longer shocks or spacers. Sometimes changing the shock angle by moving the mounts will raise or lower the rear of the bike. You want to raise it to steepen the fork angle. This is going to take some fiddling with to get right, but you will have a better ride when you get done.
The 1/2' gained by changing front tire size may or may not be important in the overall equation. Also the difference in tread patterns front and rear may work for or against you as far as the shimmy goes.
Change one thing at a time. Since you have clearance problems at the front fender and the perception that the forks are too softly sprung, start there. If the shimmy comes back after you modify the front suspension, see if you can get it right again by adjusting the rear suspension.
Then, if you need to, play with the tire/wheel size.
Originally written by skiri251 on 4/23/2007 5:24 PM
...Maybe I should get another set of CB forks on eBay. It usually goes less than 50 dollars a set.
If you look at buying a second set of forks, seee if you can find forks that will fit your triple trees that put the axle in front of the forks. It looks like your current forks have the axle centered. Moving it in front of the forks is an effective way to reduce trail.
I remembered that I do have that Bridgestone S11 front tire in my garage!
It came with the CB750 when I bought it. It's mounted on cast wheel.
I compared the two (bridge and dunlop) but I didn't see one inch difference in diameter... Nonethless I will try putting it on (with cast wheel) to see if that makes any change. (After I try the spacer..)
As for the leading axle fork legs, I found one from '82 CB750C on eBay ($54+S/H).
The question is the brake caliper. I want to keep my spoke wheel so CB750K caliper must be mounted on CB750C fork leg (unless CB750C rotor can be mounted on K spoke wheel). The design is completely different so it may be a challenge. I sent email to the seller for the fork leg dimension.
My superviser (in NY) wasn't there yesterday. So I sent him an email today. Hopefully he will respond so that I can make a reservation for STEP.
Spacers worked!
I put 30mm ones in. It raised the ride height but no wobbles!
I guess soft springs lowered the resonant frequency.
Now the soft rear suspension is even more noticeable.
I found shocks for '80~ CB750 (about an inch longer than mine) on eBay so I will get them.
I think that once you mount the shocks that the 1 inch difference will go away because of preload unless you measured your shocks in a free state (off the bike)
Ted
The seller states that '80~ CB750 shocks measure 14" eye to eye whereas pre-80 CB shocks are 13.25".
Mine got very little preload (the 2nd from the softest) right now so I figured 14" shocks with full preload even if that does not raise the rear would be an improvement.
Besides, it's only $9.99 (hopefully stays that way..) + S/H.
I have rear lowering kit (again came with the bike when I bought it) so if I can put it backwards then that will work also.
>>>I have rear lowering kit (again came with the bike when I bought it) so if I can put it backwards then that will work also.<<<
Note that if the lowering kit is the type that changes the angle of the shocks it will typically create a softer feeling suspension than stock.
It is of changing the angle type.
It's not on the bike now. I took it off long time ago because the exhaust header scratched the ground on right turns.
Shigeo,
I tried to pm a reply to you but it didn't send.
Email will work better than the pm system here if you have questions about the class. you can reach me at info@adventuresidecar.com.
Weather in June is usually pretty good, mild temps little or no rain, but anything is possible in the Pacific Northwest. We could hit a rainy weekend or it could be sunny. A little of both is at least an even bet. Bring raingear and hope it isn't needed.
VW
