Warped Rotors / Brake Judder / Tires Cupped (strut issue?)

[atruelunatic]

A whole lot of info here, but I think this will better suit the Suspension/Brakes/Chassis forum than the Wheels/Tires forum.

This is a bit of a read, but I wanted to get in as much info as I think is relevant. Thanks a bunch if you stick all the way through!

Here's the issue: When I brake from high speeds, I will feel brake pedal shake a bit (I believe the common term is brake judder?). I brought it in for a service and they have the issue caused by cupped tires. I took the wheels off and do see that all wheels are cupped in the inner corner. The fronts show the cupping a lot more than the rear.

The thing is, I do not have any shake while cruising/accelerating/most everyday braking. Again, I only get the brake pedal shake when braking at a bit past highway speeds coming down to about 20-30 mph. I am thinking this is due to the rotors, but not 100% sure.

I had a 3rd party shop take off the wheels and examine the rotors and they have the outer lip of the rotor measured at 29.9mm and the thinnest portion of the rotor measured at 28.44mm, a difference of 1.46mm. They threw out a number of 1.14mm being the largest difference in rotor thickness. Does anyone have solid facts about this being the spec for OEM rotors? I'll pull the wheels off and take a straight edge on it also to see if there's a big gap between the straight edge and rotor and will update later tonight (it's like 95 deg out there right now!).

Back to the tires cupping: This is probably due to running the struts (KW V3) at close to the fully hard setting for bump (rebound was set correctly at KW's recommendation for starting out with). Could anyone else confirm if they think this is the reason or if there could be another reason. The wheels are fine and are balanced. I have used this setting (ughhhh) for about 10k miles, do you think that I busted the struts by doing so and need to get them rebuilt? I just fixed the setting now so hopefully this'll be fixed--the tires have probably 4-5k of life on them.

Thanks again for sticking through! I hope I can get some good opinions and insight from everyone here.

[Helmsman]

Originally Posted by atruelunatic

A whole lot of info here, but I think this will better suit the Suspension/Brakes/Chassis forum than the Wheels/Tires forum.

This is a bit of a read, but I wanted to get in as much info as I think is relevant. Thanks a bunch if you stick all the way through!

Here's the issue: When I brake from high speeds, I will feel brake pedal shake a bit (I believe the common term is brake judder?). I brought it in for a service and they have the issue caused by cupped tires. I took the wheels off and do see that all wheels are cupped in the inner corner. The fronts show the cupping a lot more than the rear.

The thing is, I do not have any shake while cruising/accelerating/most everyday braking. Again, I only get the brake pedal shake when braking at a bit past highway speeds coming down to about 20-30 mph. I am thinking this is due to the rotors, but not 100% sure.

I had a 3rd party shop take off the wheels and examine the rotors and they have the outer lip of the rotor measured at 29.9mm and the thinnest portion of the rotor measured at 28.44mm, a difference of 1.46mm. They threw out a number of 1.14mm being the largest difference in rotor thickness. Does anyone have solid facts about this being the spec for OEM rotors? I'll pull the wheels off and take a straight edge on it also to see if there's a big gap between the straight edge and rotor and will update later tonight (it's like 95 deg out there right now!).

Back to the tires cupping: This is probably due to running the struts (KW V3) at close to the fully hard setting for bump (rebound was set correctly at KW's recommendation for starting out with). Could anyone else confirm if they think this is the reason or if there could be another reason. The wheels are fine and are balanced. I have used this setting (ughhhh) for about 10k miles, do you think that I busted the struts by doing so and need to get them rebuilt? I just fixed the setting now so hopefully this'll be fixed--the tires have probably 4-5k of life on them.

Thanks again for sticking through! I hope I can get some good opinions and insight from everyone here.

Hey man, front apparently 30mm new and 28.4mm done: Have a look here for further details: http://www.m3post.com/forums/showthread.php?t=698382

Cheers

[I///MBack]

Im pretty sure you will need new front rotors, if your car is under warranty still, be sure to remove the front spacers if you have any before you take it in. If not BMW will try to blame spacers, the brakes on the M3 are good but not for long. Im on my second set of front rotors, because of the vibration due to warping

[1MOREMOD]

Warping highly unlikely. Pad deposits almost always the culprit when brake judder. Bmw dealer doesn't know the difference.

[roastbeef]

brakes could be shot, but if you have a higher mileage car and you track, maybe its time to start looking at control arm bushings. sometimes problems like this aren't just one thing like just the brakes. it could be worn bushings wearing on other components causing the brakes to feel juttery, but its your alignment that is out of spec causing your tire wear.

[dazzabb]

Have a look at this from Stoptech...pretty much disregards warped discs - in fact he says he has NEVER seen a warped disc.

http://www.stoptech.com/technical-su...nd-other-myths

I only post this as I have an intermittent, braking from high speed only shudder...I also have 380 mm Brembo's so I would be amazed if I could get them to warp on the roads around here!

[M3Bimmer77]

I suggest doing a test: speed up to about 60 mph and brake 25%, do you feel anything? Then brake 50% and then all the way. Does the vibration increases? If yes I will guess it's rotor wrapping. You can check them. House version test: Take the wheel off and set some kind of a plastic stop perpendicular to the rotor. Then start rotating the wheel and see how much the stick moves. If it moves a lot I suggest taking the car to a brake shop to make a better testing of them.
The tire cupping might be caused by several things, bad shocks, bearings, bushings, alignment, balancing....

[techwhiz]

Originally Posted by M3Bimmer77

I suggest doing a test: speed up to about 60 mph and brake 25%, do you feel anything? Then brake 50% and then all the way. Does the vibration increases? If yes I will guess it's rotor wrapping. You can check them. House version test: Take the wheel off and set some kind of a plastic stop perpendicular to the rotor. Then start rotating the wheel and see how much the stick moves. If it moves a lot I suggest taking the car to a brake shop to make a better testing of them.
The tire cupping might be caused by several things, bad shocks, bearings, bushings, alignment, balancing....

Rotor warping a myth. See what Stoptech says:
http://stoptech.com/technical-suppor...nd-other-myths

[1MOREMOD]

Originally Posted by techwhiz

Rotor warping a myth. See what Stoptech says:
http://stoptech.com/technical-suppor...nd-other-myths

+1000. people keep thinking they are warping rotors on the street. Right near imposible to do at track.

[atruelunatic]

Originally Posted by M3Bimmer77

I suggest doing a test: speed up to about 60 mph and brake 25%, do you feel anything? Then brake 50% and then all the way. Does the vibration increases? If yes I will guess it's rotor wrapping. You can check them. House version test: Take the wheel off and set some kind of a plastic stop perpendicular to the rotor. Then start rotating the wheel and see how much the stick moves. If it moves a lot I suggest taking the car to a brake shop to make a better testing of them.
The tire cupping might be caused by several things, bad shocks, bearings, bushings, alignment, balancing....

What do you think would be the best way to go about figuring out what's the source of the cupping?

C&C have my car right now for other work and verified that the alignment was good.

Is it possible that it was because I set the bump too stiff on accident?

Pretty sure BMW won't cover anything under warranty due to adding coilovers so pretty much gotta go through independent shops.

[M3Bimmer77]

Originally Posted by atruelunatic

What do you think would be the best way to go about figuring out what's the source of the cupping?

C&C have my car right now for other work and verified that the alignment was good.

Is it possible that it was because I set the bump too stiff on accident?

Pretty sure BMW won't cover anything under warranty due to adding coilovers so pretty much gotta go through independent shops.

Cupped or sometimes called scalloped dips on the surface of the tread could be suspension issues, such as loose or worn ball joints, wheel bearings or even bent parts. Worn shock absorbers or unbalanced tires or wheels can also cause cupping. I have heard that even bad brake rotors can also cause cupping. I guess this is your case.

I would lift the car on jacks and start moving things around. Nothing should be loose or have any play. Most of the times the alignment shop will tell you what's causing the cupping.

Where on the tire is the cupping? Inner, outer or middle?
How old are your shocks? check the rotors for evenness or if they are worn over the min thickness I would just change them. It's a DIY thing. It requires a little bit of elbow grease, 12 pack....of Gatorade and some $$$$. But it's a doable DIY.

I am not the guy to ask about shocks and coil overs. I know very little about them. The only coil overs I would use are Dinan.

[WingZeroX5]

Buy / borrow a set of the most abrasive racing pads you can find and use it for a few hundred miles with city traffic. The pads will pretty much scrape the brake surface clean for your equipment of choice.

That's how I fixed my brake judder issues. No such thing as warped rotors, it's your brake pad deposits if you did the above mentioned brake test. I've spent a long time diagnosing issues like this when it becomes apparent on my vehicles. Now I have a set of Hawk racing pads just in case it comes up again. Much more economic solution than replacing rotorss and suspension if everything else checks out.

[1MOREMOD]

Brilliant.