Rear-end wiggle when braking

[d3vi@nt]

During a recent quick stop from 40mph I felt the rear of the bike (M695) kind of wiggle side to side a bit, not sliding almost wobbling. Conditions were warm and dry and no skid --I felt it was a controlled stop. I've read that this can be due to suspension, or rider technique. The bike is new to me, so I don't really have a point of reference for this behavior.


FWIW, the tires are the stock Bridgestone Battlax's with about 6300 miles (previously owned by a non-aggressive rider). They still have plenty of tread and proper inflation. I had the local dealer do a safety inspection after I bought it and everything checked out.  If it's rider-caused, I assume I need less front brake and more rear. Otherwise, I'm not sure...

[thought]

it sounds like you applied too much rear brake and just had it break loose.  how old are the tires?  if it's over 3-5 yrs old, they might be just too old and hard to be giving you enough traction and thats why it broke free.

seeing that it's a 695, i'm guessing that the tires are at least 4 yrs old if it's a 07 model.  you might want to look into spooning new rubber on even though you have enough tread... dry rot and age are a distinct possibility now.

[stopintime]

When you apply the front brakes, the bike really wants to keep moving - so the rear will try to find a way through. It's not possible to find a way through, so it's forced to/ tries to go around or over. The result is a light rear end and often a wiggle..

Apply brakes with better modulation, if you can, then the wiggle won't be serious.
(little or no rear braking)

+1 on new tires - stock Battlax 14s are not very good and on their way to being off by age.

[d3vi@nt]

Thanks for the feedback.  I neglected to mention that it was a straight-line stop. If I locked the rear, I would've expected a pretty smooth skid, though. Guess I better go find an empty parking lot again.

@thought: you're correct, it is an '07.  Sounds like I better heed everyone's advice and find some new tires.

I wonder, would tweaking the suspension in any way help to reduce the lightening of the rear under braking, or is that even remotely logical?

[stopintime]

Thanks for the feedback.  I neglected to mention that it was a straight-line stop. If I locked the rear, I would've expected a pretty smooth skid, though. Guess I better go find an empty parking lot again.

@thought: you're correct, it is an '07.  Sounds like I better heed everyone's advice and find some new tires.

I wonder, would tweaking the suspension in any way help to reduce the lightening of the rear under braking, or is that even remotely logical?

For the bikes with Marzocchi forks there's not an easy fix, but changing the springs and using heavier oil will help quite a lot.
The stock fork compresses too fast, it changes the bike geometry and weight distribution = easier to skid because of a light rear end.
If you weigh more than ~160 - it's a good modification. New rear spring while you're at it.

[thought]

Thanks for the feedback.  I neglected to mention that it was a straight-line stop. If I locked the rear, I would've expected a pretty smooth skid, though. Guess I better go find an empty parking lot again.

@thought: you're correct, it is an '07.  Sounds like I better heed everyone's advice and find some new tires.

I wonder, would tweaking the suspension in any way help to reduce the lightening of the rear under braking, or is that even remotely logical?

np man, and that rear end wiggle happens in a straight line with too much rear brake applied.  in general, you just want to try to be easy on the rear brake to keep that from happening.

[IdZer0]

Not sure, but I think rebound to slow on the rear shock can also cause this. Maybe check that rebound is in the middle of the range (i.e. default setting).

[ODrides]

I'd bet you had the clutch engaged. The wiggle comes from the discrepency in speed between the front and rear tires. The rear wiggle is a very common occurence at the track under hard braking, in which case the front tire is braking hard and the rear is engine braking after down-shifting (with no conventional brake applied). Remember, as you brake, weight goes forward, so the front tire has more traction to brake harder. The rear will get light. Clutch in and the rear won't object. That's fine for a panic stop, but not for cornering, when you want to have the clutch engaged so you can get back on the gas.

[d3vi@nt]

I'd bet you had the clutch engaged.

Ok, now I'm busted. Clutch was disengaged and I didn't have enough time (or reflex) to downshift. I wonder if I had downshifted quickly enough things would have seemed more normal.  Still, the front seems to dive significantly under hard braking.

All in all, I've gathered it's a traction issue due to weight distribution. So, new tires = better traction, tuned suspension = better traction, and improved technique/braking modulation = better traction.

Thanks again guys/gals.

[CDawg]

I wonder if I had downshifted quickly enough things would have seemed more normal. 

If you do not have a slipper clutch, make sure you rev match otherwise you may chirp the rear tire.