Rotor Warping Explained by a Brake Engineer [Archive]

Craig99SE2

07-02-2003, 12:24 PM

Myself and a fellow co-worker (a DSM guy) had a chat with our resident brake engineer. We were curious about the causes of rotor warpage. Here is a synopsis of what he told us:

Rotor warpage is ONLY caused by crap rotors!

Now the reasoning behind it ... A rotor is simply malleable metal which means over time, it will move. If you start with a true rotor, centrifugal forces have nothing to do except cancel themselves out and the rotor will run true. Even when the caliper depresses, by design they compress equally on both sides and front-to-back over the length of the caliper WITH RESPECT to the trueness of the rotor. Again, it will wear down the surface, but do so evenly!

Now, take the same rotor that is untrue. As you drive it, centrifugal force is magnified at the spot in which the rotor is untrue and the face will slowly move and worsen the untrueness.

Also, by driving in the city, this condition is lessened because the pad is grinding away the untrueness. However if you do a lot of highway driving, you are more prone to warp.

Bottom line is that Pontiac has junk rotors. I'd bet that it is a pretty loose tolerance for the supplier in order to keep cost down, thus the rotor faces are untrue. This would explain why EVERY Grand Am is prone to this and why EVERYTIME rotors from the dealer are installed, it happens again!

As for the guy with Brembo/EBC pads ... Brembo sent you some crappy rotors! I'd gaurantee it wouldn't happen with their $400/pair rotors!

You get what you pay for folks!

Gimli

07-02-2003, 01:19 PM

Originally posted by Craig99SE2
This would explain why EVERY Grand Am is prone to this and why EVERYTIME rotors from the dealer are installed, it happens again!

Really? Hmmm, must not be a Grand Am I bought then because I've never had a brake problem. Must not have been Grand Ams I've rented at least 10 times either cause I've never had bad brakes on any of them, and some had over 100k km on them.

I guess your "brake engineer" also never heard of warpage caused by uneven heat transmission to the rotor has he? Something that commonly happens when you're running hot rotors (because you just had to brake hard, your calipers are stuck pressing the pads on the rotors or race pads) and you drive through water.

Also, by driving in the city, this condition is lessened because the pad is grinding away the untrueness.

Really? What kind of hardass pads do you use? Pads don't grind away rotors, unless they're completely worn ant it's not the pad making contact but the metal plate behind them. If that was the case you'd change your rotors every 30k miles, not the pads. Rotors are made to be stronger than pads for that exact reason.

Even when the caliper depresses, by design they compress equally on both sides and front-to-back over the length of the caliper WITH RESPECT to the trueness of the rotor. Again, it will wear down the surface, but do so evenly!

Can your "brake engineer" explain why the inside brake pad usually wears off quicker then the outside pad? Methinks it's because the pressure isn't applied evenly on both sides...

Craig99SE2

07-02-2003, 01:59 PM

Originally posted by Gimli
Really? Hmmm, must not be a Grand Am I bought then because I've never had a brake problem. Must not have been Grand Ams I've rented at least 10 times either cause I've never had bad brakes on any of them, and some had over 100k km on them.
Whaddaya want a cookie? And your point is??? You want facts, look at the number of car models out there with the number of brake rotor warpage problems per model.
I guess your "brake engineer" also never heard of warpage caused by uneven heat transmission to the rotor has he? Something that commonly happens when you're running hot rotors (because you just had to brake hard, your calipers are stuck pressing the pads on the rotors or race pads) and you drive through water.
Yes he has, but that accounts for a whole ... what ... 2% of warpage issues
Really? What kind of hardass pads do you use? Pads don't grind away rotors, unless they're completely worn ant it's not the pad making contact but the metal plate behind them. If that was the case you'd change your rotors every 30k miles, not the pads. Rotors are made to be stronger than pads for that exact reason.
I never said x microns/day! When 2 objects rub together, there is friction, friction causes wear. Measure your rotors now and in 2 months re-measure. $200 says you get a different number. Now, common sense would kick in and say "Hey Gimli... we aren't talking about millimeters ... were talking microns"
Can your "brake engineer" explain why the inside brake pad usually wears off quicker then the outside pad? Methinks it's because the pressure isn't applied evenly on both sides...
Mine wear evenly. Yes, in theory it is a "floating caliper". In reality it is not 100% equal.

OK, is it me or did you come off as a total :knob:

Don't shoot the messenger jacka$$! And sorry, but the guy has done this for the last 10 years ... I think I'll keep my money on his theories ...

Kdawg207

07-02-2003, 02:01 PM

I know nothing about this kinda stuff...all i know is both My GA's had warped rotors before 12,000 miles. Maybe i drive too hard but they should make it longer than that. But $300 later I fixed that

PACE

07-02-2003, 02:09 PM

All I know is

2000 Grand Am GT- Brake pads and rotors replaced 3 times under warrenty before 24,000 miles....

2003 Grand Am GT- BRAKES SOUND LIKE CRAP!!!! I'll be taking it in this week to get brakes fixed....

My experience....GA brakes suck!

Gimli

07-02-2003, 03:27 PM

Originally posted by Craig99SE2
OK, is it me or did you come off as a total :knob:

Don't shoot the messenger jacka$$! And sorry, but the guy has done this for the last 10 years ... I think I'll keep my money on his theories ...

Wow, that's real mature, I should've known name calling wasn't far behind. Next time I'll just shut up and let you do your little know-it-all stunt.

...or maybe not. Because some people actually know they don't know everything and they might be interested in learning actual information instead of pseudo-expert opinions. I think I'm interested in their education more than in your 15 minutes of glory.

Tough luck... what new name are you going to find to call nme now or are you gonna be the perfect little kid and keep calling me the same?

Craig99SE2

07-02-2003, 03:49 PM

Originally posted by Gimli
Wow, that's real mature, I should've known name calling wasn't far behind. Next time I'll just shut up and let you do your little know-it-all stunt.

...or maybe not. Because some people actually know they don't know everything and they might be interested in learning actual information instead of pseudo-expert opinions. I think I'm interested in their education more than in your 15 minutes of glory.

Tough luck... what new name are you going to find to call nme now or are you gonna be the perfect little kid and keep calling me the same?

DUDE ... WTF?!?! What is your ailment? What have I ever said or done to you? Get a hobby! All I did was post the results of my conversation and I thought a few people here might want to hear what he had to say. If that's being a know-it-all, then so be it! You can address me as "Almighty Craig" from now on.

Then, you turn around and jump all over my sh*t ... and for what purpose? Your first response to my post was the most immature thing in this whole damn thread!

AMRAAM4

07-02-2003, 04:08 PM

Thank goodness Gimli has already handled it so that Craig won't have a bug up his ass again with me, because although true, I don't find the "brake experts" explanation very earth shattering. I tend to think it could be explained a different way

Craig99SE2

07-02-2003, 04:17 PM

Originally posted by AMRAAM4
Thank goodness Gimli has already handled it so that Craig won't have a bug up his ass again with me, because although true, I don't find the "brake experts" explanation very earth shattering. I tend to think it could be explained a different way

Somehow I knew Bob would chime in sooner or later! :D

luniz

07-02-2003, 04:17 PM

It is interesting to see the explanation; however, when it comes to Grand Am's, no explanation is needed. Everyone should just know that the rotors Pontiac uses for the GA suck!

The people I truly feel sorry for are the GA owners who pay the Dealerships to put on OE rotors when they can get better rotors for the same or less price.

The same thing applies to GA owners that replace their tires with the same crappy RSA's that came with the car. I mean the Goodyear store near me sells them for 175 a peice! Obviously you can get them much cheaper, but not everybody knows that.

PACE

07-02-2003, 04:26 PM

Originally posted by luniz024

The same thing applies to GA owners that replace their tires with the same crappy RSA's that came with the car.

I have Michilin Pilot Sport's.....but I think the RSA is a good tire....

luniz

07-02-2003, 04:36 PM

Originally posted by ECAP
I have Michilin Pilot Sport's.....but I think the RSA is a good tire....

Treadlife is good, but I am not happy with them. When I was looking for tires every salesperson I talked to said how bad the RSA's are. Then I go to tirerack.com and look at the reviews from customers and wonder how people would even pay 130 a tire let alone 175 a tire from Goodyear stores.:confused:

So the phrase 'you get what you pay for' doesn't always hold true. But then again, that is just my opinion.

PACE

07-02-2003, 04:42 PM

I hear ya....once you buy a performance tire you never go back.....as to the argueing above in this thread I present this award to one one in particular....just think its funny.....

cavingman

07-02-2003, 04:43 PM

Originally posted by luniz024

The people I truly feel sorry for are the GA owners who pay the Dealerships to put on OE rotors when they can get better rotors for the same or less price.

yea, but free warranty work is a whole nother thing... :D

luniz

07-02-2003, 04:48 PM

Originally posted by cavingman
yea, but free warranty work is a whole nother thing... :D

I feel the same way. Thats why I said I feel sorry for someone to pay for the OE rotors. I knew when my rotors were bad that I could either get new OE rotors for free or just buy better ones. I chose to get them serviced and when the warranty is up, buy either Brembo or Powerslots. Hell I would tell anyone to at least get the rotors serviced once before the warranty expires to prolong the time before you need to get new ones.

Gimli

07-02-2003, 05:33 PM

Originally posted by Craig99SE2
DUDE ... WTF?!?! What is your ailment? What have I ever said or done to you? Get a hobby! All I did was post the results of my conversation and I thought a few people here might want to hear what he had to say. If that's being a know-it-all, then so be it! You can address me as "Almighty Craig" from now on.

Then, you turn around and jump all over my sh*t ... and for what purpose? Your first response to my post was the most immature thing in this whole damn thread!

I'm sorry but I never attacked you personally. I did counter your arguments but when you say things like:

"Rotor warpage is ONLY caused by crap rotors!"
"Even when the caliper depresses, by design they compress equally on both sides and front-to-back over the length of the caliper WITH RESPECT to the trueness of the rotor."
and
"This would explain why EVERY Grand Am is prone to this and why EVERYTIME rotors from the dealer are installed, it happens again!"

that are simply not true you have to expect people to say something.

I never said you were a liar, never said you were stupid and never said that the rotors GM puts on the Grand Ams are perfect.

I did invalidate your arguments with verifiable facts though, which seems to have offended you. Then you called me names.

If there's one thing I,ve learned by frequenting internet forums it's that most "experts" are self-proclaimed and know a lot less then they think. When even I (who isn't a car expert by any measure) can counter their arguments in less than 5 minutes that makes me think twice about their opinions. maybe you should do the same with your expert friend.

You know, I'm sure there's an expert somewhere who thought putting a boat fan in front of his intake would make the best turbo. A lot of people buy these "turbos" because an expert says so. Fortunately I know better, and I think you do too...

AaronGTR

07-02-2003, 06:32 PM

Although I've never had any problems with my old brakes, I agree that pontiac put cheap brakes on the car. Mainly they are under sized for the weight of the car and that can cause overheating, which causes weak braking. It some times , though seldom, can lead to warping.

The brake pads do NOT wear evenly on the rotors however. The calipers are single piston floating design, which means when the piston moves out it pulls the caliper in and puts pressure on the outside pad. But it puts more pressure on the inside pad so it wears faster. It is this one single way that the caliper functions in addition to braking over bumpy surfaces that most commonly leads to warping. When you brake over rail road tracks for example, the tire bounces up in the air for a split second and locks up, then starts moving again when it hits the ground. The metal is malable over time (as craig stated) and the uneven pressure on the inside of the rotor when the pad grabs as the wheel starts moving is what deforms the metal. The solution is don't brake heavy over bumpy surfaces. Quality rotors and calipers can help the problem somewhat but not eliminate it. Take car of your brakes and they'll take care of you!;)

Licit

07-03-2003, 03:30 AM

I've never had warping on my 99 GAGT and I still have all stock rotors at 85,000 miles. It's funny though because I can compare between my car and my buddies 00 GAGT. I took my car in for brake work once and have done it ever since myself. He always takes his in for brake work at a shop. He'll be getting his 3rd set of rotors with 77,000 miles on his car later this summer. Turning the rotors is not necessary except if there is warpage or scarring. High rate of replacement for GA's probably does have alot to do with the fact the rotors are middle-of-the-road quality but if you get them turned every time you get new pads no wonder you need new ones often. Another friend works at Midas and he said the replacement size on GA rotors is fairly high, so he replaces rotors on them earlier than on another brand of car that may have the same rotor thickness. Plus it's up to the brake guy whether he tells you that you need rotors. As for the GA brake system they should have at least put a dual piston setup on it.

VaGT

07-03-2003, 07:52 AM

Originally posted by Gimli
Really? Hmmm, must not be a Grand Am I bought then because I've never had a brake problem. Must not have been Grand Ams I've rented at least 10 times either cause I've never had bad brakes on any of them, and some had over 100k km on them.

Well, even if the tolerance is off, they can still get lucky once in awhile. They go with the lowest bidder on rotors, then jack the price to $200 each if you want to replace them. My future brother in law is a GM tech and vouches for their low quality rotors.

Maybe the grand ams you rented 10 times were not running on their stock rotors.

The only thing Craig is "guilty" of is using the words "every" etc instead of "most".

I have owned 2 cars prior to this one. A 95 Escort that I bought with 11K miles on it, and a 98 Avenger that I bought new. I got 50K out of each before I had to do anything with the brakes.

I drove the Escort and the Avenger more than my wife at the time, so the driving on those was more aggressive than the driving has been on the GA... since I drive my beater car mostly.

Tack on that we have kids now, and we both drive more carefully. My wife is extremely easy on the brakes.

There is NO REASON other than crappy parts, tolerances, whatever that I should warp brakes. I don't speed and then slam them on. I rarely go above 70 because I only make about 3 long highway trips a year. GM puts HORRIBLE rotors on the Grand Am, and it is pathetic how long they have continued to do so. ADD $100 TO THE PRICE OF THE CAR FOR BETTER BRAKES. ONLY A MORON WOULD THINK THAT WAS WASTED MONEY.

scooby2

07-11-2003, 12:28 AM

Went through 3 pairs of OEM rotors on my '99 within the first 30k miles. Put the power slots on at 30k and 55k miles later they are still working as good as day 1.

They will probably need changed when i hit 90k in the next couple months but talk about a difference!

Avsguy01

07-11-2003, 07:10 AM

My rotors are already warped at 9,000 miles on my new 2003 grand am. The started warping at 5,000. Can i go to a dealership and get them to completely replace my rotors or do i just get them turned? I dont have the money to get all new brakes and rotors. I had a 2000 grand am before that and i had the same problems and had them turned 3 times and it just got worse each time. Until i bought my own cheap rotors and brakes is when my problem was solved. I think my warrenty should give me new rotors. 9,000 is too early to be having these problems.

Gimli

07-11-2003, 07:16 AM

They'll turn them first until they get too thin to be turned again. Then they'll change them (if you're still under warranty).

Avsguy01

07-11-2003, 07:18 AM

Okay gotch!! I have 75,000 warrenty so yes they will be changing them eventually lol Thats if i dont get aftermarkets by then. I think im getting them turned with my oil change next week:) I just cant believe 9,000 miles and these damn things need turning already. I love my grand am but the brakes suck!!

MIAaron

07-15-2003, 04:27 PM

64K miles and my rotors have been fine. I thought they were warping at one time but it was due to other issues. I am only replacing them now cuz the pads need to be replaced for the second time and I don't think they will last another 30K. And I tow a 2000lb BOAT frequently.

I have noticed one thing about the ga brakes though, they are a LOT more touchy when I tow the boat. When I say touchy, I mean very little fade, very less peddle movement, and an overall "firmness" to the braking. I wish it was that way all the time. :confused:

Avsguy01

07-16-2003, 06:39 AM

Just had my turned yesterday under warrenty at 10,000 miles.

atc3434

07-16-2003, 11:45 PM

I think I'd have to agree, the brakes on the Grandam are WAY undersized. IF you have to brake hard, you'll heat them right up. I have a brake problem right now, I'm thinking bad pads and rotors, cause under full braking force, I can feel the pedal bottom out, and she stops decently, but not anywhere near tire locking ability. And a hard stop from only 30 mph, and I can smell the brakes. Not cool. Definalty not a fan of the GA brakes. Not enough proportioning to the rears either. Makes those babies WORK.

mfuller

07-17-2003, 12:14 AM

The rotors really need to be an inch larger in diameter and .1" thicker. The front-to-rear balance is fine; you absolutely do not want your rear brakes locking up....ever.

Happiness is doing 10 back-to-back 60mph to 10mph stops with no loss of braking power....:thumbs:

Mike Jung

07-17-2003, 11:17 PM

Originally posted by MIAaron
64K miles and my rotors have been fine. I thought they were warping at one time but it was due to other issues. I am only replacing them now cuz the pads need to be replaced for the second time and I don't think they will last another 30K. And I tow a 2000lb BOAT frequently.

I have noticed one thing about the ga brakes though, they are a LOT more touchy when I tow the boat. When I say touchy, I mean very little fade, very less peddle movement, and an overall "firmness" to the braking. I wish it was that way all the time. :confused:
PSST!

The 99+ GA (with the 3400 V6 engine) is only rated in the owner's manual to pull/tow up to 1000lbs/450kg.

I hope you are using gear selection 3 (& NOT D, overdrive) when towing it.

atc3434

07-18-2003, 12:54 AM

I'd have to disagree about the brake bias being good. Strong rear brakes are nothing to be afraid of, IMO, just respected. I'd rather have all tires reach the limits of traction at the same time, or maybe the rears just a fraction sooner. I absolutely don't want to understeer braking into a cornor and slid straight when I can instead induce a little oversteer. After the Camaro, oversteer is a FWD is a snap. So healthy strong rear brakes, and respect for them, can make for sweet driving capabilities.