[ben1364]

The E90 brochure indicates that the 330i front rotors (disks) are 13.0" and the rears are 13.2#. Likewise it says that the 325i front and rear rotors are 11.8". Typically front rotors are larger than rear rotors since they typically perform some 70 to 75% of the work. Any idea why the E90 cars have rear rotors as large or larger than the fronts; or do you suppose the diameters in the brochure are incorrect?

[E90Fleet]

Many cars these days have larger diameter rear brakes ( eg E90 and E46 M3) than front brakes
But the rear brakes are thinner

So the fronts still have more heat capacity
Also the rear brake pad is smaller

[JVFan]

So what is the rationale for larger rotors then?

[E90Fleet]

Just to get perfect brake balance for the way the weight is distributed on the car


On a side note they look better than tiny brakes

[stevebmw3]

Rear brakes must also include HAND BRAKE and its needs place.

[visor]

Also for more braking of the driving wheels during dtc/dsc intervention due to greater engine hp and torque.

[romeo26]

off topic
can you put 330 brake on 325?

[E90Fleet]

Originally Posted by romeo26

off topic
can you put 330 brake on 325?

Not without changing the calipers, DSC system, brake master cylinder, car software

So basically NO

[onesixeight]

Originally Posted by romeo26

off topic
can you put 330 brake on 325?

The 330i brakes aren't all that much better...

If you're going to spend money on 330 brakes, get a StopTech or Brembo BBK...they are designed to work with your standard master cylinder and DSC system.

[nexus66]

Since the rears have the drum brake inside the hub, then the rear disk, although larger in diameter probably has a smaller surface area for actual braking.

Can't get to my car to check/view this personally, so correct me if I'm wrong!

[ben1364]

Thanks guys. I haven't noticed cars with rear brake rotors the same diameter as fronts before. Oh well. I guess I don't get around much! <g>