Front end wobble under heavy braking

[Teh_K]

Hey all,

It seems like my handlebars have a slight left/right wobble when braking very hard (braking for T1 at VIR S, for example). It doesn't happen most of the time, but if I'm really diving those brakes down, a slight wobble emerges.

Any ideas on what it could be?

The bike is all stock for an 08 GSXR, but I'm running Vesrah pads. My first guess would be maybe low front tire pressure? I'm running Pirelli's (DRC), which have a softer sidewall, so I wonder if the tire is deforming too much. I run about 30F/29R hot.

Thanks for any help.

 

[moto1320]

Ever have Chuck set up your suspension? Can you tell if you're blowing through the travel on your forks?

 

[avizpls]

30/29 seems more like a cold pressure set up to me (tho I'm first to admit no experience with pirellis)

Head bearings could also be a factor, and definitely, as the banana jockey suggests, have your suspension set up-- or at least do a zip-tie test

 

[dickiedoo]

Is it possible you're feeling the tire slide for the first time ever? It's a strange feeling, but when I push a front under heavy braking It makes a feeling similar to what you're saying.

 

[finny47]

Have you checked the rim and rotors for wobble? Put the front on a stand or wheel balancer and see if one of the rotors have an issue. Hard braking you will feel the carcass moving around more.

 

[Teh_K]

moto1320;279263 wrote: Ever have Chuck set up your suspension? Can you tell if you're blowing through the travel on your forks?
I keep meaning to get it setup, but haven't yet - I'll do it next time I'm there. I don't think I'm maxing out fork travel, but I guess that's a possibility. I did a zip tie test last year just to see how low it was getting, but without knowing the bottom-out height, I guess it's of little use.

avizpls;279273 wrote: 30/29 seems more like a cold pressure set up to me (tho I'm first to admit no experience with pirellis)

Head bearings could also be a factor, and definitely, as the banana jockey suggests, have your suspension set up-- or at least do a zip-tie test
It's hard to nail down track pressure for the DRCs... I should contact Pirelli. This last weekend, my rear was looking really good as far as wear (i.e. not tearing), but my front consistently has melted-on rubber pieces (debris patch) in the center. Not sure if that's relevant.

dickiedoo;279278 wrote: Is it possible you're feeling the tire slide for the first time ever? It's a strange feeling, but when I push a front under heavy braking It makes a feeling similar to what you're saying.

Is it possible to push a front under braking when straight up and down? I'm not sure how much a tire could slide when not leaned over.

finny47;279279 wrote: Have you checked the rim and rotors for wobble? Put the front on a stand or wheel balancer and see if one of the rotors have an issue. Hard braking you will feel the carcass moving around more.

I put new tires on this year, and the rim looked great on the balancer, but I didn't check the rotors... I would think that warped rotors would cause a wobble at all braking intensities.

 

[bboynicku]

dickiedoo;279278 wrote: Is it possible you're feeling the tire slide for the first time ever? It's a strange feeling, but when I push a front under heavy braking It makes a feeling similar to what you're saying.
Yea when i'm really braking hard (summit main down the front straight for T1) is used to feel the same. It a slow left and right movement of the bars. I'm curious now too...

Teh_K;279253 wrote: Hey all,

It seems like my handlebars have a slight left/right wobble when braking very hard (braking for T1 at VIR S, for example). It doesn't happen most of the time, but if I'm really diving those brakes down, a slight wobble emerges.

Any ideas on what it could be?

The bike is all stock for an 08 GSXR, but I'm running Vesrah pads. My first guess would be maybe low front tire pressure? I'm running Pirelli's (DRC), which have a softer sidewall, so I wonder if the tire is deforming too much. I run about 30F/29R hot.

Thanks for any help.

 

[barry38]

My bet would be your bottoming the suspension. And if you are locking your arms under braking and transmitting that energy into the bars/forks, all you have left is the flex in the tire carcass. If the forks aren't sprung for your weight, and you haven't set the compression/rebound properly, you are asking for issues. Get your baseline suspension set-up, ride it, and if you are still having issues, then start looking at other things.

 

[vinny337]

+1 to what Barry said have your baseline, sag, etc. setup. You may want to make sure you have your forks serviced with fresh fork fluid.

 

[TProc]

spring rate

How much you weigh???? Are you within range???


Co-signing on Barry's post.

 

[avizpls]

you know, another thought is that the front wheel may be straight, but in fact the rear end is sliding around? Could be from downshifting, engine braking or actual rear brake combined with all the weight on the front. And it sort of gives the same feeling of the bars wobbling. With the gopro mounted on the bars, another guy has a good video of this sitting on a memory card from this weekend.

 

[Meat]

Once I had a front end shake under hard braking into T10a at Rd Atl. I sprayed tons of brake cleaner on the rotors, scrubbed them with a greenie, and went back out. The shake was gone and never returned.

 

[matt2212]

Meat;279392 wrote: Once I had a front end shake under hard braking into T10a at Rd Atl. I sprayed tons of brake cleaner on the rotors, scrubbed them with a greenie, and went back out. The shake was gone and never returned.

^^^^^^
This


Sent from my iPhone using Tapatalk

 

[ritelite77]

That debris field on your front tire is an indication of too low of pressure. I too get this debris field. You can clean it up by gradually adding pressure, but keep in mind it may change your feel for other portions of the track. I prefer a softer front for more feel. But I I've never had a wobble of worry due tire flex under hard braking. I'd check/correct stem bearings, suspension, brakes, and geometry. Your problem will be there somewhere.

 

[matt2212]

ritelite77;279433 wrote: That debris field on your front tire is an indication of too low of pressure. I too get this debris field. You can clean it up by gradually adding pressure, but keep in mind it may change your feel for other portions of the track. I prefer a softer front for more feel. But I I've never had a wobble of worry due tire flex under hard braking. I'd check/correct stem bearings, suspension, brakes, and geometry. Your problem will be there somewhere.

Are you sure you are getting more feel? Or are you deadening the feel with soft tires?

 

[avizpls]

"feel" is ambiguous. TO ME a lower pressure tire has more feel in the snese that it has more flex and motion and the fronts moving around on you more. A firmer tires gives more feel in the sense of feedback; you can feel the tire's grip level and bumps in the road etc more.

 

[matt2212]

avizpls;279446 wrote: "feel" is ambiguous. TO ME a lower pressure tire has more feel in the sense that it has more flex and motion and the fronts moving around on you more. A firmer tires gives more feel in the sense of feedback; you can feel the tire's grip level and bumps in the road etc more.

What do you call soft? 2lbs low or 5?
I asked the question to the op so he would think about it, I understand what you are saying but my question still stands are you truly feeling what the tire is doing in regards to grip if it is flexing and moving because of pressure?

 

[avizpls]

matt2212;279470 wrote: my question still stands are you truly feeling what the tire is doing in regards to grip if it is flexing and moving because of pressure?

Concisely: No. You feel it doing something, but i don't think its telling you much about grip at that point.

 

[virtualsolitude]

barry38;279313 wrote: My bet would be your bottoming the suspension. And if you are locking your arms under braking and transmitting that energy into the bars/forks, all you have left is the flex in the tire carcass. If the forks aren't sprung for your weight, and you haven't set the compression/rebound properly, you are asking for issues. Get your baseline suspension set-up, ride it, and if you are still having issues, then start looking at other things.

A guy named Peyton mentioned getting my suspension setup as a 'must-do' for anyone. That it could be done for $40.00, I recall. I need to get my suspension setup. It was pretty bouncy at JC. Can someone provide Chuck's name?

 

[avizpls]

chuck