Crazy Wobble in higher speed turns

My bike is a 76 kz900 A4 completely stock. I am not a racer. My riding skills are average and improving. I don't care that much for going fast until I see a corner. Whether on my mountain bike, in my car or truck, on skis, or on my motorcycle, I love to carve as quick as I can. Lately I've ridden the new Whistler highway a few times early in the morning. The posted limit is 80kph/50mph. This a new state of the art road.

I was going quick in the turns. Hard, but not that hard, maybe 7/10ths. 130kph/80mph in some of the curves. The bike had lots more to give and me too. Centre of the curve the bike wobbles and chops really bad. Both directions. Scares the shit out of me. The bike tracks well with no problem at 100 + mph even when decelerating hard.

Last spring had new fork seals, swing arm bushings, tapered steering head bearings, and tires (Bridgestone Battlax). I am 6ft tall and 160 lbs. I run the tires at 28 psi ft, and 32 psi rear.

What could be the problem? I was nowhere near the point where I had to hang off the bike. Is it me? Is it common with these bikes? There is no problem going hard in tighter turns or straight line. Just going fast in medium-long radius curves.

have you checked steering head gusset area for cracks? maybe tighten steering head bearings,wheels in line? could be many things

Plummen,

I believe the wheels are well aligned, no dog tracking, and no hands tracking is true as can be. The head bearings are as tight as can be without being stiff.

I just removed the tank and there is no sign of stress in the head gusset area. I used a flash light a magnifying glass for inspection.

The one thing I have noticed of late is that there is a slight amount of cupping of the front tire. It is even on both sides. I believe it is normal wear. Some people will dispute this I'm sure. There is about 8000 miles on the tires and they are in good condition.

if the tires are cupping that would be a good place to start, whats the max air pressure on your front tire?

Max is load is 507lb @ 42 psi cold front, 633lb @ 42 psi rear cold.

I,ve been running at 28-30 front and 32-34 rear. The FSM says 28 front and 32 rear.

id go with the air pressure rating on the tires.did this just start recently ?

I've had the same problem in the past. Tire had cupping. Changed tire and wobble went away.
In my opinion you are running to low of air pressure.
Here is a quote I found and it's the method I use:

The best rule of thumb is that your hot tire pressure should be between five and ten percent higher than the cold pressure. That is if you inflate the tires to 36 psi when cold, when the tire is hot it should be 38 to 40psi. Any more or less and the tire is over or under-inflated. This rule also takes into account the varying loads you could put on your bike.

I've used this method for years and it works for me. Also, I have no cupping on my tires.

Plummen,

I didn't notice it all until recently, and have pushed it quite hard in the past, but no more than recently either.

I'll take it back to the dealer on Tuesday and see what they say about the cupping.

Seems to me that with my light weight (157 lbs) that 28- 30 psi in the front should be OK.

Tony,

A friend of mine that I ride with quite a lot has a 83 GL 1100. He had quite a bad wobble any time he took his hands off the bars. New tires and the wobble went away.

My tires are relatively new. Only a year old, and running at recommended pressure. Shouldn't be a problem, but I'll look into it when I get a chance.

Any other ideas?

If u look at the "patch" that small front tire puts on the ground, and realize thatin an 80mph curve and u leaned over the patch is going to be even smaller,cupping and curves =disaster.I would replace that 8k tire with a new one,especially since u have tightened up ur steering head.If that doesnt work,mount a steering damper-I used one from a 600 Gixxer.I had a speed wobble on a new tire at 75-80 and the damper took it out.bj

Exactly what is a steering damper, what does it look like, how do you install it, and more importantly, how does it work?

i like what everyone said so far and i agree on all points....

i still think what i originaly thought after reading just the posts title though..

new rear shocks............


they can be found cheap but is once again ,just like the front rim dealy....you would have to watch the bids on a good used clean set...i had stiff s&w yellow shocks on my kz900 when i first got from the p.o and in any of the shocks settings they were still too much or not working right..another member here swears by em thoguh...anyway not your shocks..but my point is that rear shocks suck the same in too much or not enough...can cause the same type sweeper screw jobs....imo

i did all my little free tricks to set up the bike to behave like my old days kz's and could not get away from a shudder heading fast- half -fast into entries to big-medium sweeping corners...the shudder set up the rest of the corner/corners(think telemaking :woohoo: ) to handle like shit....i wanted to have a bike that was fun to pull the trigger on corners and was sad thinking i was dealing with a possible lemon....

i knew it was the shocks ,but untill i could find a set ,that conclusion was just a guess...

i soon scored a deal on koni's with clicker settings...

probelm solved 100%.......

s&w street strokers(the blue spring ones) are showing up but they're finish is weathered on most sets....they are a gauranteed improvment..even if a guy had to fix the paint....koni's are rare and cost$....these are the only two brands i have used with 100% rear end fixes...

i think your shocks are in need of an upgrade..it sounds like your getting to pushing harder and have expossed the shocks as ready to push harder too...imo

Galactica wrote:

Max is load is 507lb @ 42 psi cold front, 633lb @ 42 psi rear cold.

I,ve been running at 28-30 front and 32-34 rear. The FSM says 28 front and 32 rear.

Why are you not following the manufactures recommended air pressure? Is there a reason you are running 12 to 14 psi lower than the tire manufacture recommends. That is possibly the root to the cupping which is probably the root to the wobble.



The factory shop manual is for OEM tires and the technology has changed since then. Always follow the manufacture recommendation for any tire.