Called Germany Today...
 

Anyway as some of you might remember I went to the BMW Ultimate Driving Experience where I got to look at and drive the new 330 sedan. While looking at it I noticed that 1) the brakes are f'ing huge on this car! and that 2) the ones in the back actually seem bigger. To my suprise they were. The rear brakes are 13.2" while the front are 13.0" now the front ones are slightly thicker and both sets are vented so my question is why? Sure I can theorize and guess but I wanted a direct answer from BMW.

I have so far asked to no avail:
Local BMW dealerships
U.S. Customer relations
Munich, Bavaria Headquaters

I will write a letter to their headquaters in both the U.S. and in Germany hopefully to get someone in the engineering department because it seems to be impossible to do so over the phone.

Anyway, I guess I'm asking for some ideas, advice, forum contacts etc.
Oh and here are some pics:
http://www.bmwusa.com/NR/rdonlyres/5.../0/0642_01.jpg
http://www.v6performance.net/gallery...663_series.jpg
Site indicating that the rear brakes are indeed larger (I have checked with more sources so it's not a typo).
http://www.bmwusa.com/vehicles/3/200...n/techdata.htm

when you get an answer let us know

i believe its because the rear brakes have more inertia on the axle since they are connected to the drive train, therefore to bring the rear wheels to the same rotational speed at the front you need more force, which is done by larger brakes.

to repaat myself.

the front wheels have less mass, therefore require less force to slow them down. the rear wheels have larger mass since they are connected to the drive train, therefore they need more force to slow them down.

thats just my theory.

Still the weight of the car shifts foward requiring the majority of the braking to be done on the front. The wheels are the same size so they have the same mass. They probably wanted more mechanical adbantage on the rear since they wanted probably to keep the same size caliper and pads. I think it might have something to do with the electronic equipment keeping the cars balance in check.

I made another thread about this at htp://www.E90post.com
http://www.e90post.com/forums/showth...7801#post17801

edit: I'm leaving the country tomorow and going to Russia as a Long BEach representative for the Sister City Association and won't be back till July 20 so don't expect to many replies from me.

Have fun! :wave:

Don't these brakes have a pad wiper for when they get wet from rain?

Alright I'm finally back from Russia and no they don't have pad wipers they just periodically come really close to the rotor in order to dry the pads in preparation for braking in rainy conditions.

They need larger brakes in the rear, because during deceleration in a RWD car, the rear brakes ALSO have to decelerate the drivetrain (engine, transmission, driveshafts, differentials, etc.)

In FWD cars, the rears only have to decelerate the back two wheels and nothing else, that's why we usually have to have HUGE brakes up front for any stopping power

-James :cool:

That would be a nice explanation but the majority of cars no matter RWD or FWD don't have larger rear brakes. See what we were trying to explain was why the change over the last 3 series, obviously as you can tell we came up with some good ideas.

Also to comare the Ford GT being a mid-engine car with RDW has 13.2" rear brakes and 14.0" front brakes and it has a 43%/57% weight distribution.
http://www.fordvehicles.com/fordgt/specs.asp

It's possible they are using larger rotors that require less actual braking force from the calipers, instead of smaller rotors and more expensive calipers.
(BMW Cost cutting? :eek: ) just speculating ;)

-james

it bigger in rear because the need something to keep the 50/50 weight ratio .. hahahahah

yeah, i'm gonna guess it has to do with balancing the car. maybe a more neutral braking is achieved with the larger brakes in the rear?

The NSX has a 41/59 weight distribution* and has slightly larger rear brakes.

Front - Ventilated, 11.7 in. diameter, 1.1 in. rotor thickness*

Rear - Ventilated, 11.9 in. diameter, 0.83 in. rotor thickness*

*2005 USDM NSX Specs

my friend's friend's explanation thru IM :)

Part of this could be explained by the new larger parking brake mechanism
that BMW started using on certain E39 and E46 models.

Or, more likely, since there's so much more DSC activity going on, the
larger rotor is required to combat excessive wear and heat. They're
probably adjusting the brake balance with smaller pistons in the rear,
although quite frankly the rotor diameter difference is not all that much
from previous models... and previous models have always needed more rear
brake anyway, which BMW started to realize with the larger rear brakes in
the E46 M3.