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Speed wobbles

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Each of the last two races, I got a case of the speed wobbles. Two weeks ago I was doing full on tank slappers for a hundred yards. I was in a soft spot and tried to wreck myself to end it, but I ended up highsiding myself back on to the seat and kept going. Last week, I tank slapped right into a turn and the front end stuck and I was able to ride away. Very lucky both times.

I know a stabilizer helps. My RTT is a POS and doesn't do anything, but being budget challenged (i.e. broke now), I need to wait before I get the triple clamps to mount up my Scotts.

What causes the wobbles? I am hoping that if I know what makes it happen, I can adjust the throttle or my body position to avoid them for now.

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I believe they are cause by a gyration effect initiated by the front wheel getting out of alignment with the back wheel from hitting a small rock or a bump. When you are going down a strait transfer your weight to the back of the bike and keep a solid grip on the bars. Once they have started they are very hard to stop. However, they are relatively stable and you shouldn't freak out if it starts. They only way i know of how to stop them is to stop the bike.

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Beside accelerating / decelerating, feather the front brake or if its really bad apply a bit more. Loading the front suspension seems to help stabilise things.

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I know every situation is different and this seems to be one of those topics that everyone has their own personal opinions on but here's what seems to work for me. Loosen up your grip on the bars, get your weight off the front wheel and be smooth with the throttle either giving it more or getting out of it. On streetbikes I've noticed that the steering dampers help, but they're not a cure all as I've still had a few nasty ones on my GSXR. I've not yet felt the need for a damper on my dirtbikes, the tank slappers I've had there have seemed a ton mellower! Good luck!

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I had tank slap on a freinds modified Katana 750. I'm sure my dirt bikes all do it but after that nasty slap doing 100 I probably don't feel it.

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Perfect race yesterday to "practice" the speed wobbles on. Really long, fast valley crossings. I had a couple minor instances of them, and I was taking notes. Thankfully they never turned into full fledged tank slappers.

It seemed that when I was in a neutral bike position they were more prevalent. Hanging over the bars when cruising or leaning way back and pulling up to speed, they never seemed to happen. The only thing that I changed was cranking my stabilizer all the way up. With about 100 yards of tight stuff over a 41 mile loop, there was very little need to have the bars loose.

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are you riding a 04 YZ250? if so then you shouldn't have any tank slap at all, I think you need to check the balance between the fron and rear suspension.

Push down on the bike and see if either the front or the rear come up first - I think your answer my lay there somewhere.

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My understanding is it is from the forks being to vertical, which is unstable. (think shopping cart wheel) This could be not enough rear sag or to much front sag or a bad design. (prob not in this case) Once the wobble starts your in trouble because it tends to magnify itself. The trick is not having it happen in the first place. Check your suspension setup, odds are that's it. If it does happen (and we are talking headshake, not a back end swap here) get ur weight all the way back and give it full throttle, smoothly. If you can make the front end light the fork angle will increase and no more problem... or your gonna be going twice as fast when you crash if it doesn't work.

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I would lean towards a suspension problem for consistent tank slapping. A steering damper can mask the problem if you crank it up tight. It has to do with suspension and steering geometry. The next time you push a grocery kart watch for wheels that essentially flop back and forth like your handlebars do - this is with a vertical or 90° pivot.

The more you rake your forks out like a chopper the harder it is to steer and technically harder to tank slap. The closer your steering axis is to vertical (shopping kart or older metal kids tricycle) the sharper you can turn, but it's usually too twitchy and difficult to control at any real speed. Crotch rockets typically seem to have sharper steering and are more prone to tank slapping.

So, to potentially fix the problem check your bike to make sure the front end isn't diving when you jump on the pegs. Also having your forks too high in the triple clamps has the same effect - for high speed stability put your fork caps flush with the top of the triple clamp. Once this problem is solved you can use your steering damper for its intended purpose instead of masking a suspension/setup issue.

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Thanks for the input guys. I know it is hard to pin down a problem that someone types into their computer, but taking a little bit from each of you seems to be pointing me closer to the problem.

Forks in the triple clamps, a contributing factor I believe. In checking on my bike, it looks like I have them about halfway up. I prefer the technical and twisty stuff, and now that it is mentioned, I don't remember sliding them back down since I laid out our enduro. I will try to remember that for the next fast race.

Suspension, another likely factor. I have had my suspension revalved and sprung and ever since then, I have been chasing my tail. My suspension guy is at almost all the races, and is continually tweaking on it to try to make me happy. The back is good, I am happy with it and the sag is checked very regularly, but the front is giving me problems. Thinking back, it was at the beginning of the latest round of changes that this started happening. I will be passing this along to him so we can go back to where we were last month and try something else.

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