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One of my bikes is an old XS650 Yamaha 650cc vertical twin that I have tweeked out the suspension and installed some stickey tires. I love to run the twisties on the old bike because it has tons of torque and is pretty nimble. On a recent ride, I was on one of my favorite roads which has a long steep up hill left hand sweeper, I love to enter at about 45 mph, and hit it hard and squirt out the other end about 85 mph. The last time I did this, the bike went into a head shake and speed wobble at about 75 mph that nearly turned my hair white. On the way home I was trying to figure out what happened to the bike, in a streight line I could actually feel the bike resist if I tried to lean right of left. A quick trip to my workshop reveled nothing wrong with the steering head bearing, forks, swing arm, or chain line up. Much to my chagrin, I found the rear tire had lost it's crown, with only 3,500 miles on the clock, it looked like a big wide racing slick. The sides had plenty of rubber, but the center was gone from streight line acceleration. $120.00 later and a new tire, I think I have the problem corrected, but I don't know if I have the nads to find out . XS

You might want to add a steering dampener/fork brace.

DivideOverflow wrote:You might want to add a steering dampener/fork brace.

Either that or balance. Have you bothered to check the balance of the front wheel?

Sticky tires and skinny forks.... headshake is bound to crop up when hammering corners. Physics can be a blitch. Firm up the front end with a brace..... or different(thicker, stiffer) forks would be ideal, but more involved in terms of work and cash outlay.

When modifiying any motorcycle it usually turns into a quest for the weakest links. Adding a few ponies and stickier tires normally results in finding suspension weaknesses. Wobble/head shake can usually be corrected with the addition of a steering dampener which is where I would start. Then i would go to a fork brace, but you probably won't need one.

Might be that you unknowingly switched to radial tires on an older frame that was designed with bias ply tires in mind...

Perhaps its something those bikes are prone to? I also had an XS650 twin that went into a tankslapper (at 100+ mph). At the time, I thought it was the handlebar mounted windshield that caused it. So, I took it off and replaced the front tire. But, to be honest, I didn't have the balls to go over 65 on that bike ever again.

Outlaw, I heard that ! The problem is, if the problem has been fixed, where can I get a volunteer with big enough nads to test it for me?

Know any squids?

ride it on out to harrisburg...one of my crew mates would be happy to tear up some moutain roads for you. he rides one. he is crazy good on it. he'll keep up with the ducatis we run with.