Tank slappers/tyres

[slopster]

I've got a 96 gsxr 750 and have been through a couple of sets of tyres on it now. It has always been prone to having a bit of head shake when the front end is light under power but once your used to the feeling it doesn't really bother you too much because its fairly predictable and not severe. Anyway I just replaced my pilot powers with a set of m3's and while I'm generally pretty happy with the tyres I noticed straight away that it was head shaking a lot more under similar conditions in fact I even had my first lock to lock tank slapper (It was a pretty rough bit of road and I powered through it without any real drama fortunately). Its shaking my confidence a bit. What can I do about it given that the only factor that has changed is a new set of tyres and also I went from a 180 rear to a 190.

[98tls]

Does that thing have a steering damper ?

[slopster]

No no steering damper I realise a damper would improve things but I'm more concerned about how the tyres have changed things.

[98tls]

Some will say it will be slower to turn in with a 190 but it shouldnt give you slappers,what size rear rim on the 750?

[slopster]

17" rear rim

[98tls]

I meant the width mate,Just a theroy and dont quote me on it at all but maybe its the 190 on a rim thats not as wide as it should be,i have a 190 on my TLS and am betting its got a wider rear rim than the Gixxer,as i say may be off the mark but worth considering,hopefully someone with some expertise will chime in.

[slopster]

It says 17X6.00 in the workshop manual so I'm guessing 6" width. On paper it is supposed to have 190 on the back but I've always had 180 but thought I'd try a 190 this time round.

[98tls]

OK well thats my theroy fucked then,best of luck getting it sorted eh.

[HDTboy]

I've just worked through this problem on the 1000, it's at a point now where I'm comfortable riding it fast, and it's on Dunlops (notorious for wiggling).
Bring it over some time if you want to have a bit of a play with suspension settings

[Gremlin]

off the top of my head, first, when getting fresh tyres the profile will obviously be heaps better than the worn tyres. Profiles also differ between models of tyres. I also never found much difference between a 180 and 190 (even same model of tyre) on my 7r, which didn't have a damper either. Had some pretty wicked lock to lock slaps a few times too.

Is the suspension set up for you? Rough roads can also make the bike more prone to misbehaving, as it gains and loses contact with the road.

[F5 Dave]

Well here's a theory, probably not very palatable but here goes; Your suspension is old & needs a thorough recondition + the springs could also have sacked out. Steering head and swingarm/linkage bearings play a part if knackered.

Still it is worth persevering, they weren't a bad bike. Time to bring it back to new or better.

[riffer]

Going up from a 180 to 190 shouldn't stuff up the steering too much but if your steering head bearings are getting loose you'll definitely get tank slappers happening.

My FZR used to tank slap something stupid under power until I redid the steering head bearings. The RF shook its head as the front came up when coming out of corners fast but tightening the head bearings fixed that.

Check your steering head.

[Jinx3d]

Is that the 750 T? Awesome bike.

The first thing I'd do is check your tyre pressures, my bike was 10 psi low stright out of the tyre shop, - must need there gauge calibrating.

Then I'd get the steering head bearing replaced, not just tightened. I have had a set that felt perfect but the bike had a shake. I replaced them and the old ones had the tiniest marks but after replacing them it was solid as a rock.

Next, I'd look at you free sag and +rider sag, to make sure the front and back are resonably similar. If the problem is on bumpy roads it may be your spring rate is too high, but unless you are exceptionaly light I would think this would be the problem.

You could also check the rear arm bearing and chain tension to make sure the back it able to move freely.
Finally, if the new tyre is higher, this could be steeping the rake angle enough to aggravat e teh shake. Apparently (Super bike magazine) ajusting the rear ride height to account for tyre wear is actually a good thing to do if you are trying to achieve optimum set up.)

I'm a bit of an arm chair expert, but I have just been through all this on my own TL.

Good luck!

[notasothers]

My mate had a similar problem on his bike, I took it for a spin and it totally freaked me out, this thing was all over the show. As it turns out his front forks were a little loose (the bike shop picked it up with his last service). Now its sweet as... and he still cant keep up.
Could be something worth checking out?