High Speed Wobble/Down at 65MPH

Hey Guys!

I just wanted to know if any of you have ever had a problem with a high speed wobble? That is what caused me to lay my bike down at 65mph. It started when I was running about 75mph. I tried to control it by slowing down but it didn't work. I knew she was going to throw me, so I tried to make it to the grass. Well I didn't quite make it. I hit the pavement at 65, tucked and rolled for about 200 yards, and got up and ran to the side of the freeway. Luckily no one was following close behide me or I would have been roadkill. I"d had it wobble on me before, but it had never been uncontrolable. Anyway, my question is if any of you know what causes that, and if you do, what can I do about it? I know I needed new tires at the time. I am now in the middle of repairing my bike and found some tires that are suppose to reduce the high speed wobble. I was also wonder if using a steering stabilizer from a later model bike would be feasible. I have one more question as well. Does anyone know where I can find chrome aftermarket wheels to fit my bike. I am really wanting to make this a one-off motorcycle. Well hopefully someone can answer my questions. Thanks for your time!

Have you checked the play in the steering head, I had tank slappers on a goldwing once, slowing it down got worse lucky I was only doing 40, had to accelerate out of it then slowed down really slow, got back to the shop and found loose steering head. did not happen after that. I believe you can get uneversal steering stabilizers just have to find an appropriate place to mount it

So far I've been fortunate not to experience anything like that. My guess is to check the steering head bearings. After a while they'll wear a flat spot and a common replacement is tapered roller bearings.

I've not had this happen on a streetbike but on MX and Enduro bikes and quite often it is caused by not enough rebound on the rear shock(s), But I'd check the steering head bearings first.
For the steering dampener, yeah they definatly help.

Ive had that at 100 miles per hour .Its scary.Make sure the tires are balanced and steering head is tight and rear wheel is parallel to front wheel.U should measure the rear axle to the swing arm pivot and make sure both sides are the same.u cant always trust the marks on the chain adjusters.Good luck.

Sorry to hear about your mishap - never happened to me and I hope it never will. The wobble can be caused by a number of things: worn/unbalanced tires, worn or loose steering stem bearings, worn/loose swingarm bearings, worn wheel bearings or a combination of the above. That is what I would check, also check that all fasteners are tight and torqued to spec.

I have to disagree on the steering dampener though - first of all you shouldn´t need it on a 650 and it won´t make the problem go away, it´ll only disguise it. Much better to find out what caused the wobble and fix it instead.

650CSRrider as to your question about wheels. I've got the same bike and wound up swapping mag wheels off a 550 LTD onto mine. It is 100% bolt on no mods needed. I suppose you could have these wheels chromed if it were in your budget, I just met a guy the other day that did that on a 1000 ST he told me it cost him like $500.00. Your other options would be to just work like heck and polish them or I suppose you could also have them powdercoated. There is a huge choice of colors available in powdercoat I'm sure you could find a color that comes close to looking like chrome. That might be your best option since in order to make chrome last on aluminium you have to have them triple plated which can get expensive. I like both the look of the mags and the fact they are far easier to maintain than spokes. Here is what your bike will look like with mags.

uneven tire wear
worn steering head bearings
spindly forks
worn swingarm bearings
wire wheels out of true

The Z/KZ family is kind of famous for the tank slapper. If you haven't ever experienced it, it ain't no joke... usually, most of the bikes will be OK till they hit one of those reflective deals embedded in the middle of the road... then the bike start oscillating with the oscillations getting worse and worse... then it is called a TANK SLAPPER... It is probably worse to try and ease off the throttle... probably would be best to get on the power but it has happened to me and I never can remember this... good thing you weren't hurt! It has happened to me but at a bit higher speed and it gives you time to reflect on your own mortality!

About the only thing similar is to have a flat in a tube type rear tire at 60 mph... the air goes out REAL FAST and you are left on a squirming tire that is also causing the bike to wiggle like a worm...

Post edited by: wiredgeorge, at: 2007/06/23 10:17

Several more neglected items:

Correct air pressure in the tires
Even amounts of fork oil in the forks
Worn rear shocks (esp. where the damping fluid has leaked out)
Wrong tire sizes for the bike
Mismatched tires / wrong tire types
Rear wheel misaligned

Selecting the correct tire for your bike makes a huge difference in how the bike handles. Most of these older bikes benefit from ribbed or semi-ribbed tires on the front.

Post edited by: Jeff.Saunders, at: 2007/06/23 10:25

Jeff said it best, wrong tires. I have found this to be the tankslap problem on all the KZ bikes that were stricken with it. Ribbed front tires eliminate the problem completely most of the time.

The 550 I had would shake it's head around 90mph, found that the steering head nuts were loose, and that the tires I had at the time (Metzeler 880) contributed to it. The bike I have now was labeled as a twitchy tank-slapper, so much that Suzuki retrofitted steering dampers to them.

650CSRrider wrote:

Hey Guys!

Thanks for all of your input. If everything goes good, I will be completely rebuilding my 650 this upcoming winter. I will double check everything you guys metioned to make sure this problem doesn't strike again. Hopefully I will have my bike ready repaired enough to ride a little while before winter hits, but when winter gets here, the complete restore will begin. Thanks again for everyone's help!