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Discussion Starter #1
I found this on Turner Motorsport's page:

"New M5 Euro 2pc. front brake rotors, only 22.5 pounds each. These two piece floating rotors are lighter and transfer less heat to the hub assembly than one piece rotors. $279"

Naturally, the question is raised, why did BMW put on better brakes for our pals on the other side of the Atlantic? There has to be a caveat, but what?

I mean, what's the DEAL?! <seinfeld>
 

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Someone humming down the A1 at 140+ may well have occasion to use their brakes hard repeatedly as the occasional Ford Fiesta pulls out to pass.

You have a lot of thermal shock asking a stone-cold rotor to dissipate 100mph in a hurry, and the floating rotor design is less likely to warp/crack in these conditions.

I suspect the reasons Americans don't get them are:

1) A perception that Americans don't have occasion to use their cars in this manner.

2) Experience shows that Americans tend to run weeping to their dealers at the slightest noises coming from their brakes; floating rotors tend to be noisier.

3) The rotor-to-hat interface is a wear point, and BMW warrants the cars longer in the US.

So, BMW puts (a) quieter (b) cheaper and (c) less likely to cause warranty replacement (if not used hard enough to warp/crack them) one-piece rotors on the US cars to save themselves grief.
 

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Discussion Starter #3
Thanks for the explanation JEM! Guys like you make this board kick ***.
 

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This has been asked many times before. My understanding then, and now, is that for BMW there is some sort of legal issue regarding liability. Not to say that the Euro rotors are weak... I am sure that someone has the exact details out there.

Depending on how you drive, you may not notice. The US brakes will fade more due to heat transfer, which will become apparent on the track or when stopping frequently from autobahn speeds... but you shortest initial braking distance from 60 or 80 will not change (not on the first try, anyhow). Dan.
 

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i thought the design was floating calapers, not rotors?!?

my understanding is that bmw was concerned about liability in the us. ie, getting the crap sued out of them, with a class action claiming neglegence on bmw's part

apparently, the floating rotor/calaper design is such that if it fails, it fails catestrophically, where as the standard design, if it fails, it tends to still partially work so you can limp home.

that was the word that i heard
 

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Discussion Starter #7
I can't see how catastrophic it can be if happens to only your front brakes (keeping US spec rear brakes) sure the braking would suffer greatly, but you could still "limp" around.
 

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No, it's floating rotors.

The rotor and hat are two separate pieces so that the rotor can expand/contract as it heats/cools.
 

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"...can't see how catastrophic it can be if happens to only your front brakes..."

Just the opposite... if your front brakes go, and your rears are engaged, you will end up with massive oversteer and a likely disaster if rounding a corner with any speed. Dan
 

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I read about this subject about a year ago.

Appearently the floating discs will only last about 100K miles, or Km. But it had to do something with European owners keeping their cars longer than owners do in the states. So an origional owner is going to know the whole history of the vehicle. So they will know when it is time to replace them. So in the U.S. when the car reaches 100K, it may be on its 3rd owner and that important fact about the rotors may not have been passed on. So the BMWNA has the cars built with the solid rotors.

It's not that the 2 peice rotors are illegal, it's just a liability issue.

* When the 2 peice rotors fail they will crack, which can be very dangerous. (A peice of the rotor will break off.) Now imagine what would happen when you apply the brakes hard and the disc has a peice taken out of it. So they put on the cheaper and more durable rotors common to most every other car.
 

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here in europe we do a much more intensive use of our cars....and if the brakes weren't floting to prevent cone distorsion and fissures we have to change rotors every month....in my porsche i do 25.000km with the rotors...and then they crack..........
 

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and the e39 m5 floting rotors have a cryogenic treatment.....much more harder then convencional steel rotors...
Never knew that.....mind me asking...where you got that info ?
 

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Factory BMW Motorsport Floating rotors that have been Cryo Treated to offer better longevity.

Floating Rotors offer some of the best advances in Brake Technology. Lighter weight means better performance. The unique bonded hat and rotor face allows greater heat dissapation. This means better performance, and better longevity. What more could you ask from a brake rotor?

These rotors are not cross drilled.



Brakes // Brake Rotors // BMW E39 // HMS Motorsport
 

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The describtion is a little vague...

Factory BMW Motorsport Floating rotors that have been Cryo Treated to offer better longevity.

Brakes // Brake Rotors // BMW E39 // HMS Motorsport

From the description, on this supplier's website, it seems to me that they are the ones that subsequently cryo treat the factory BMW Motorsport floating rotors.
I have these rotors and the dealer never mentioned any factory cryo treatment.
 

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Factory BMW Motorsport Floating rotors that have been Cryo Treated to offer better longevity.

Floating Rotors offer some of the best advances in Brake Technology. Lighter weight means better performance. The unique bonded hat and rotor face allows greater heat dissapation. This means better performance, and better longevity. What more could you ask from a brake rotor?

These rotors are not cross drilled.



Brakes // Brake Rotors // BMW E39 // HMS Motorsport

they are not bonded, its simply a heat shrink.

Is there any record of a M5 compound brake disk ever failing catastrophically?

I suspect BMW was cutting corners for the US market, as the car prices there are much lower than here.
 

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there are no records of floating rotors failing... these type of rotors isn't used in normal production because they are very expensive to manufacturer, they are special rotors, and even the new m5 has floating rotors... i never driven a car with floating rotors but i imagine they must be suberb... in my porsche sometimes i avoid to use the maximum brake force at high velocities to avoid cone distorcion...
 

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I had the stock US rotors on for 77k miles, and have had the Euro floaters on for the last 31k miles. Haven't noticed any particular difference in street driving, and I do not track the M5 (have a Porsche for that). Noise-wise, I've never heard the slightest sound from either setup.

At the time that I did the replacement, I found the Euro disks online somewhere for less money than the local dealer wanted for US disks.


Steve
00 M5
 
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