Front Rotor how far out of round is OK?

[lbk]

I have a 97' GSXR-750 that I just purchase for next seasons track riding. I've ridden it on the street a little bit to try and get used to it, and I noticed a noise in the front wheel.

It sounds like the rotor is out of round a bit, basically at slower speeds you can hear it touch the pads, then not then touch agian, so on.

I took it to the dealer because originally I wasn't going to have time to look at it before my next track day, anyways that day got canceled.

They said the pads on one side looked a little worn, and put some replacement "race" pads on there. It stops fine, but I'm wondering if I should be concerned. How far out of round, do you guys think is OK for rotors. He showed me with a screwdriver that it was a bit out of round, but the mechanic said he wouldn't replace them yet, and they know I'm using it for track duty.

Thanks in advance for any help.

[EX#996]

With out actually looking at you bike and seeing for myself, I wouldn't offer my opinion.  But I would like to offer one thought.

On the street, the front brakes provide 75 to 80% of your stopping power.  Under race conditions the speed is a lot higher and brakes are used more heavily.  How lucky do you feel?

If you can afford to replace them, do so.

My $0.02

Dawn   :)

[lbk]

The cost of replacing them is not an issue at all. If I couldn't afford parts, repairs, and tires. I shouldn't be doing this.  :D

More or less I was wondering if I was being overly anal, since the mechanic said it didn't need to be replaced. My first thought was as you said, I'm riding this bike at my limits, do I really need to waste attention even thinking about the brakes.

Thanks, more or less I just needed some second opinions. Besides I have all winter to replace them.

[Litespeed]

The fact that you asked about it defaults it to needing replacement.  When you are on the race track, you do not want to be second guessing any part of the bike.  If it's bad enough to have to ask a mechanic, it's bad enough to think about while racing...

[tcchin]

Typical factory service limits for rotor lateral runout range from .008-.012". However, as little as .006" lateral runout can be felt as pulsing in the brake lever or wheel hop during hard braking.

All brake rotors will warp slightly under racing conditions and regular maintenance/race prep should include measuring your rotors for warpage. Fortunately, rotors can be trued inexpensively, but only trust your rotor repair to an experienced professional. Also, be sure that the rotor your wish to have trued has sufficient thickness, or you'll just be asking for trouble.
The frame repair shop that we use for rotor truing is capable of achieving >.001" lateral runout and charges $40 per rotor.

[Eric Kelcher]

Hey Tim who do you use for Rotor work?

I discrard rotors if you feel any pulsing in the brake lever. They get worse very quick once they start to warp. You have all winter to deal with it. I would findsome new ones or send them in to get straigthened I have never done that and have a stack that would be great to have useable again.

[tcchin]

I use Doctor John's Motorcycle Frame Straightening at 1161 North Cosby Way, Anaheim, CA  92806, 714-630-4075.

[schpreck]

Replace them.  If you have to brake hard while leaned over, your front will wash out.  I speak from experience.  get new rotors, for christ's sake!

[tcchin]

1) The performance level of straightened rotors that still meet the minimum thickness service limits is identical to that of new rotors.
2) Even the best brakes in the world cannot compensate for blatant riding errors.

[MELK-MAN]

i had warped rotors on my f4. when stopping from 75mph or so, you could feel a hard pulsing, and SEE the fork tube ends moving back and forth quickly when you looked down under the hard braking.. not fun. I went to EBC pro-lite streets, but warped these too. Finally, EBC sent me pro-lite RACE rotors at cost... and viola... no more problems after 10 track days. You do need to insert the high tollarance buttons provided after the red buttons can no longer be turned with your thumb and finger..the rings can be replaced and you keep the hub..
later.

[lbk]

Already got them, now I just have to find time to put them on, that and finish prepping the bike. Haven't had much time lately.

[mdr14]

If you can seel a wobble in the rotor when you spin it or feel a pulsing the rotor is bent.

Most likely the carrier would bend and not the rotor. I basically have never seen a bent rotor, only carriers ( which does cause a rotor to bend). As long as rotor is less than .004"-.005" your golden.

I have straightened many carriers with 100% success.

Barring a good crash, carriers can be easily bent if your not careful tieing a bike down using wheel chocks.

Also check to see if your front wheel is centered correctly. I believe on the 97 GSXR you can do this as follows: Tighten both calipers with front wheel in place. Have the the axle snugged, then loosen both sides pinch bolts. Bounce the front end several times, then snug pinch bolts, If you place the front end up on a stand, the front wheel should spin smoothly with little brake pad resistance. On the captured nut side it would be normal for it to not be flush with the fork leg.
Bikes that have the threads as part of the fork do not really have this option.

You would think that the brake pistons would be self centering, but I have not really seen this to be the case on production calipers. Every little bit helps.
If you can reduce brake drag just a little bit, you do make the brakes more effective. Brake drag can cause uneven pad wear too.

Matt Drucker