[Yogijet]

Nice work, BMW.

[S i n i s t e r]

BAD ASS! Cant weight

[lostkhan]

Losing weight from rotors and suspension counts alot more than inside the car. It's a smart move from Bmw side

[mycoupe]

It would be interesting to know the actual dimensions of those new rotors...I mean, they are saving a bit of weight, but they are also moving the moment of inertia further away from the center at the same time. So, if the weight reduction isn't high enough, those new rotors could actually hurt the cars acceleration!

[JIM E92]

very impressive stuff

[Finnegan]

Wonderful news on weight reduction efforts--especially unsprung weight, springs and wheels.

But I have to wonder what reducing that weight does to the thermal capacity of the rotors. Unless I'm way off the weight of a rotor to a large degree influences its ability to handle heat as a heat sink. M brakes have limited capacity as is in recent models, and I'm not seeing how this is going to help that much.

I can see this on family sedans and the like, not performance cars. Feel free to disagree....

[mycoupe]

Originally Posted by Finnegan

Wonderful news on weight reduction efforts--especially unsprung weight, springs and wheels.

But I have to wonder what reducing that weight does to the thermal capacity of the rotors. Unless I'm way off the weight of a rotor to a large degree influences its ability to handle heat as a heat sink. M brakes have limited capacity as is in recent models, and I'm not seeing how this is going to help that much.

I can see this on family sedans and the like, not performance cars. Feel free to disagree....

different metals have different thermal conductivities. I'm not too familiar with the figures, but the new materials could absorb and cool faster than iron rotors. I know the aluminum hats should help quite a bit with heat dissipation.

[Mooreski]

Originally Posted by Finnegan

Wonderful news on weight reduction efforts--especially unsprung weight, springs and wheels.

But I have to wonder what reducing that weight does to the thermal capacity of the rotors. Unless I'm way off the weight of a rotor to a large degree influences its ability to handle heat as a heat sink. M brakes have limited capacity as is in recent models, and I'm not seeing how this is going to help that much.

I can see this on family sedans and the like, not performance cars. Feel free to disagree....

I agree. Feel free for that?

The Swiss cheesing of the center will increase surface area and allow heat to escape to the air better, but maybe not enough to compensate for the lower amount of mass. Hopefully that is addressed somehow!

[Uli_HH]

If you take a closer look on the pics of the upcoming M3 E90 CSL/LightWeightConcept, you would see that this new lightweight brakes are on this car ... I think the new springs would also debut on the LWC!

Uli_HH

[FrankiE90]

Oh man this needs to be available now! Hopefully it fits on 06-11 e9x.

[Artmasterx]

Originally Posted by Finnegan

Wonderful news on weight reduction efforts--especially unsprung weight, springs and wheels.

But I have to wonder what reducing that weight does to the thermal capacity of the rotors. Unless I'm way off the weight of a rotor to a large degree influences its ability to handle heat as a heat sink. M brakes have limited capacity as is in recent models, and I'm not seeing how this is going to help that much.

I can see this on family sedans and the like, not performance cars. Feel free to disagree....

Originally Posted by mycoupe

different metals have different thermal conductivities. I'm not too familiar with the figures, but the new materials could absorb and cool faster than iron rotors. I know the aluminum hats should help quite a bit with heat dissipation.

Originally Posted by Mooreski

I agree. Feel free for that?

The Swiss cheesing of the center will increase surface area and allow heat to escape to the air better, but maybe not enough to compensate for the lower amount of mass. Hopefully that is addressed somehow!

For some data:
Thermal conductivities are about (W/m-K):
Cast iron: 52
1% Carbon steel: 45
308 stainless steel: 16
Aluminum: 206

Heat capacities by mass and volume are about (kJ/kg-K // kJ/L-K):
Cast iron: 0.47 // 3.5
1% Carbon steel: 0.47 // 3.7
308 stainless steel: 0.46 // 3.6
Aluminum: 0.90 // 2.4
(Aluminum is about 35% the density of steel)

Aluminum is about 4x better at conducting energy than iron or carbon steel, but with the aluminum center they have also reduced the heat transfer area (from outer ring to hub) and probably introduced some interface resistance where the hub bolts on. You have maybe 1/2 the heat transfer area of a solid steel cap, so you better off in the heat transfer by 2x.

For heat capacity, it looks like about 1/2 the volume of the hub is gone, and on a volume basis aluminum can't hold as much heat as iron. Compared to a solid iron hub, you are probably 3x worse from a heat capacity perspective (in the hub; the friction surface will still hold a lot of heat since it is heavy and iron/steel). But then the new aluminum, swiss cheese hub is probably ~25% the weight of a solid steel one.

As mentioned the hub may be more efficient at removing heat since you have more area in contact with the air, but in reality, it is probable that most heat is dissipated through the venting in between the friction surfaces since those are the hottest areas and probably have the fastest air flow.

Regardless, I am sure BMW will have thoroughly tested these to make sure they are appropriate for their application (keep fuel pump comments to yourself).

Of course, you will probably now be paying $400 for a new rotor instead of $150.

[ENINTY]

My first thought, as has been stated, is a massive increase in cost. That rotor while neat looking will be expensive to produce. Second thought is fiberglass reinforced springs... hum... where have I heard that before? Oh yes, the Chevrolet Corvette. IIRC the C3 had the first set of fiberglass springs.

Why not take the Buel motorcycle approach and integrate the rotor surface area into the inner wheel rim (basically flipping the brake inside out - putting the caliper next to the wheel hub). That would provide a huge surface area, and make the wheel extremely strong at the same time.

[hks786]

I'm all for weight saving so that is good news for sure. However, I guess I'm the only one who thinks those rotors look bad. I wouldn't want to see them things behind my wheels.

[Artmasterx]

just think of all the colors you could powercoat the inside part... the possibilities are endless.

[Imola.ZHP]

retro-fit kit for e46 please!

[bayerischeperformance]

Originally Posted by ENINTY

My first thought, as has been stated, is a massive increase in cost. That rotor while neat looking will be expensive to produce. Second thought is fiberglass reinforced springs... hum... where have I heard that before? Oh yes, the Chevrolet Corvette. IIRC the C3 had the first set of fiberglass springs.

Why not take the Buel motorcycle approach and integrate the rotor surface area into the inner wheel rim (basically flipping the brake inside out - putting the caliper next to the wheel hub). That would provide a huge surface area, and make the wheel extremely strong at the same time.

cost on rotors would not be much more expensive if at all..from the looks of it instead of replacing the disc and hat like you do with tradition rotors you could replace just the disc itself and reuse the hat.

[esqu1re]

Originally Posted by bayerischeperformance

cost on rotors would not be much more expensive if at all..from the looks of it instead of replacing the disc and hat like you do with tradition rotors you could replace just the disc itself and reuse the hat.

+1

[mycoupe]

Originally Posted by bayerischeperformance

cost on rotors would not be much more expensive if at all..from the looks of it instead of replacing the disc and hat like you do with tradition rotors you could replace just the disc itself and reuse the hat.

I have to agree with you on the cost of the part itself, but look at ALL of those bolts holding the two together! That looks like a serious increase in labor hours right there!

[montreal red]

they should just shrink the car down a little. Its ridiculous how big cars like the 3 series have grown over the yrs.

[positiveions]

Originally Posted by Jason

It's at least 44 pounds saved from the corners combined. Not an insignificant amount of weight.

It would be like reducing each of your wheels by 11 pounds each. You'd definitely notice the benefits.

"unsprung" weight has its benefits.

[grimlock]

You're never gonna see this in the 3 .. until they've put it on the 7,6,5, .. all the way down.
New stuff always costs alot more, so unless there's mpg-related urgency, it'll be a while..

[Eugene-TAIWAN]

finally