Here's the big brake track testing write-up I promised - Page 2

DZeckhausen · 24th February 2003, 17:39

Quote:

Originally posted by pride355
On most of the cars, fronts always have bigger rotor size than rears. However on E46 M3, fronts have 326mm rotors and rears have 328mm. M3 has 50/50 weight balance; so why have bigger rear rotors?
Do you know or can guess the reason??

Actually, diameter is only half of the equation. You also need to know the thickness. The thermal capacity of a rotor is determined by its mass, not its diameter. For example, the BMW X5 4.4i has 332mm front rotors and the X5 4.6i has 356mm front rotors. So the 4.6i rotors seem to be slightly bigger. But that's only half the story. The 4.4i rotors are only 30mm thick, whereas the 4.6i rotors are a MASSIVE 36mm thick. They weigh over 30 pounds each!

Getting to your point about the E46 M3, while the rear rotor is indeed slightly larger diameter, at 328mm vs the 325mm front rotors, it is substantially thinner. The rear rotor is only 20mm thick, whereas the front rotor is 28mm thick.

The reason BMW picked the larger diameter rear rotor probably has something to do with a combination of getting the other brake componenets to fit within the constraints of the suspension and wheels as well as the need to come up with a balanced brake torque. They probably have a set number of caliper pistons they can play with and they decided that, given the piston they chose, they needed a 328mm rotor to generate enough brake torque to balance the combination of components used in the front.

tfung · 24th February 2003, 19:15

wow.. long article.. I'll read it in depth later.. but I wonder if the new brembo rear brake kits would match Stoptech's as being more balanced than front biased...

DZeckhausen · 24th February 2003, 19:39

Quote:

Originally posted by tfung
wow.. long article.. I'll read it in depth later.. but I wonder if the new brembo rear brake kits would match Stoptech's as being more balanced than front biased...

I would expect the new Brembo rear kit to improve the balance over their front-only kit. The 345mm rotor and the 28/30mm pistons should produce more brake torque than the stock rears and help offset the front bias.

However, there hasn't been any comprehensive track testing done, or at least none that I'm aware of.

It would be fun to repeat the tests described in my 350Z write-up on a Brembo front and front/rear set-up. Perhaps there will be an opportunity when StopTech takes the E39 4-wheel kit to the track next month. Any owners in the LA area with Brembo front brakes and stock suspension?

TriflowM5+M3 · 24th February 2003, 19:46

LUCKY BA@TARD! I would love to have been in your shoes for a day of testing like that...yummm chicken wings!

DZeckhausen · 24th February 2003, 19:53

Quote:

Originally posted by TriflowM5
LUCKY BA@TARD! I would love to have been in your shoes for a day of testing like that...yummm chicken wings!

Keep in mind that I was jet-lagged and only got 4 hours of sleep the night before. We left for the track around 6 AM and by the time we finished cleaning up, it was around 8:30 PM. I didn't get back to the hotel until midnight. I was a zombie!

But you're right! Those drumsticks (not wings) were almost worth it and getting to zoom around on the test track in the 350Z, plus getting to participate in the testing was very much worth it. I would go back and do it again in a heartbeat. But I would bring more food next time and some sunblock.

m5monster · 24th February 2003, 20:07

Good job DZeckhausen...

TriflowM5+M3 · 24th February 2003, 20:08

I love it! I'd be a zombie for something like that...but not eating? Im not a happy camper when I dont eat for 2 hours...so i would be "Mr. Cranky"!

By the way...im anxiously waiting my pads. I wrote Tirerack a nice letter that I am sending with my Hawk Pads tomorrow. Thanks again dave...

ps...The shipping weight in my confirmation email states 8lbs. I know the "free" stoptech kit that we talked about has a weight savings but....pads and a big brake kit only weigh 8 lbs! WOW

atomic80 · 24th February 2003, 22:37

Quote:

Originally posted by DZeckhausen
At the very bottom, I have a table that summarizes all the data. So you don't need to jump back and forth.

I did see that table at the very end. I was talking about maybe building up the data tabulation as the article progresses. That way people won't have to move up and down throughout. Know what I mean?

pride355 · 24th February 2003, 23:02

Quote:

Originally posted by DZeckhausen
Actually, diameter is only half of the equation. You also need to know the thickness. The thermal capacity of a rotor is determined by its mass, not its diameter. For example, the BMW X5 4.4i has 332mm front rotors and the X5 4.6i has 356mm front rotors. So the 4.6i rotors seem to be slightly bigger. But that's only half the story. The 4.4i rotors are only 30mm thick, whereas the 4.6i rotors are a MASSIVE 36mm thick. They weigh over 30 pounds each!

Getting to your point about the E46 M3, while the rear rotor is indeed slightly larger diameter, at 328mm vs the 325mm front rotors, it is substantially thinner. The rear rotor is only 20mm thick, whereas the front rotor is 28mm thick.

The reason BMW picked the larger diameter rear rotor probably has something to do with a combination of getting the other brake componenets to fit within the constraints of the suspension and wheels as well as the need to come up with a balanced brake torque. They probably have a set number of caliper pistons they can play with and they decided that, given the piston they chose, they needed a 328mm rotor to generate enough brake torque to balance the combination of components used in the front.

Thank you for the explanation Dave. You help a lot on this topic.

MIB · 24th February 2003, 23:40

Quote:

Originally posted by DZeckhausen

I'll keep you posted as progress is made. I'm sorry to have pre-announced by so long and raised hopes. I feel like Microsoft, announcing Windows 2000 in 1998 and releasing it in 2002.

They are a good value if you compare them to other 4-wheel kits. But if you compare them to other modifications in bang-for-the-buck, they don't hold up too well, unless you include aesthetics in the equation.

It was driven by the marketplace who has been screaming for big red calipers at all four corners. (Not that there's anything wrong with that!)

If you want these for looks and for the slight improvement in pedal feel, the convenience of having the same brake pads at all four corners, and ease of rear pad changes, then go for it! But don't think you need these for extra safety or an extra edge at the track. Your money would be better spent on a Stage III suspension.

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Quote:

LOL. Your forgiven for all the great info anyway.

50 % want them for Looks. The BEast Rear wheels are far more impressive than the fronts. But everyone tends to photograph the fronts because of the big disks and pretty calipers. How much better will it look on the Big wheel.

35% is I want to track the car. I want to change pads. Probably Pagid Orange for the Street, and Pagid Black for the Track. So I can change both easily.

10% Performance increase.

5% Weight saving. Lightweight Wheels,Brakes,Hood- It all adds up.

Conditions on buying them. NO SPACERS. I always have balancing problems with spacers. It always takes Three hours to do a Balance Job. So No spacers. And they must fit under Dinan Light weight Wheels.

Our dollar just went up to .60c US today. They are getting cheaper everyday.