Bike is a XT660R wearing a set of Michelin Siracs with 20,000kms on them. The rear tire is almost bald, the front one is close to the TWI, not there yet, and horribly cupped. Problem: It weaves at low speeds (less than 30mph/50kmh) if I let go the handlebar. It pulls hard to one side, then it pulls hard to the other side and so on. The faster I go, the less it weaves. Seems to be less apparent under power. Handling at low speeds is scary, I can keep her going on a straight line, but if I try to lean/turn to the left when she is pulling to the right it will resist and then she will pull to the left, same thing to the other side, so it looks like if I was riding drunk :eek1 What has been checked: - Nothing is getting stuck in the handlebars or steering head. - Steering head bearings are fine, they are not notched, they are tight, etc. - Forks are straight. - Front wheel bearings are fine. Suspects? - The front tire? It's worn and I never had another bike with a front tire so badly cupped. Also I've read that carcass failures might lead to weird handling? A few months ago the inside of the tire had a seam open (the inner tire liner), and pinch the tube, it was fixed with a tire patch, but that might point to a carcass failure? - Not true front wheel? I've tried to true it to the best of my abilities (quite clear I should keep my day job). - Horribly squared off rear tire?
One tire bald and square, the other cupped, and you wonder why it doesn't stay true? Don't let go of the handlebars.
start with new tires. then align the wheels, and check that BOTH wheels are true and spokes not loose anywhere.
New tires are clearly in order- but you might have tightened your steering head bearings too much as well. I'd replace the tires, check alignments, and also ensure the head bearings are not over tightened. With the front tire off the ground the steering should be able to fall to it's heavy side (toward the brake caliper) under it's own weight.
OK, ok, I get it, I will change the tires... Gee, no need to get mad guys Yes, I was being cheap, I already have a set of Conti Trail Attacks waiting to go in, I just wanted to get my money worth out of those Siracs.
Tires are done, When you install the new tires try wearing off the little nubbies before the tire is bald..
I haven't touched the steering head bearings, I just checked them to make sure they were not notched or anything like that. To be honest, I don't think it was gradual, one day the bike just handled awfully. I don't even know how to describe it. And to me, those tires are badly cupped, it's my first DP bike and those are the first set of DP tires I've ever worn that far, road tires might get cupped, but not like those Sirac. The picture doesn't get the "full effect", it looks like the knobs that go past the center of the tire are more worn than those that don't, but those than don't go past the center are scalloped.
Well, took the bike to a place I know they are very good with spoke wheels as they specialize on low displacment courier bikes (90cc-250cc most of them with spoke wheels). They were about to get the bike into the shop when the head mechanic said "let me check that out..." Then he said, "there is nothing wrong with the wheel, I can't do much more than tightening the spokes and you'll ride away and come back, pissed off, because the bike feels the same", he kept spinning the wheel and said, "it's the tire, the cupping makes it vibrate, and there is a bump on it, the carcass may be damaged". I guess that pretty much confirms what I suspected. The wheel is not perfect, there is a small bump on it, or two... pothole or something, very small, but it is true. So I'll get the Conti Trail Attacks installed.
Well... It ended up being a combination of two things, the tires and the steering head bearings. I installed the Conti Trail Attacks and the weaving was gone, the bike was very smooth on the highway, but hard to keep going in a straight line at low speeds, it would pull to one side or the other (but not weave) if I took my hands of the handlebar... The steering also felt heavy, and she either refused to lean or wanted to lean too much, nothing in the middle... With the weaving, vibration and flatness of the rear tire fixed, I had no problem identifying the steering head bearing woes. Just had to clean them up, repack them with grease, and now she rides like a new bike! I guess that when your oil tank is right next to the steering head you shouldn't expect the grease to be there for too long. The front tire was definitely shot, it had a bump on it, the rear was already bald and I didn't notice until I had removed it from the wheel that it was also cupped. I guess 12,000 miles out of a set of tires wasn't bad. Actually, quite good. I also took the chance to replace the brake pads. The rear ones were squealing like a pig and the front ones were quiet, but I suspected they were done for. Turns out the rear ones were past the service limit, and the front ones past the friction material! I wonder why the front ones never made any noise.