Front Rotor

[Z42011]

I noticed that the front rotor is very different from the rear rotor on my 2011 Z4 - see the attached picture. I never read this in the brochure, but is this a floating rotor with an aluminum hub? The rear looks like a standard all steel rotor.

It is a very impressive piece of hardware.

[HerrK]

It is not a floating rotor. It is a aluminum hub riveted to the steel/cast iron rotor.

[Z42011]

Why is it constructed this way?

[tranquility]

Isn't this the EfficientDynamics feature for the Z4? Something to do w/ energy being created whenever we hit the brakes and it being used elsewhere. The amount of energy created is really miniscule, but better than nothing.

[HerrK]

Originally Posted by Z42011

Why is it constructed this way?

Probably partially for aesthetics - so you don't see a rusty hub through the wheels. Engineering wise to save unsprung weight. In a ground vehicle with a suspension, the unsprung weight (or the unsprung mass) is the mass of the suspension, wheels, brakes, rotors, and other components directly connected to them, rather than supported by the suspension.

The unsprung weight of a wheel controls a trade-off between a wheel's bump-following ability and its vibration isolation. Bumps and surface imperfections in the road cause tire compression—which induces a force on the unsprung weight. The unsprung weight then responds to this force with movement of its own. The amount of movement, for short bumps, is inversely proportional to the weight - a lighter wheel which readily moves in response to road bumps will have more grip and more constant grip when tracking over an imperfect road. For this reason, lighter wheels (and lowering the unsprung weight) are sought especially for high-performance applications.

[bmwmick]

Originally Posted by tranquility

Isn't this the EfficientDynamics feature for the Z4? Something to do w/ energy being created whenever we hit the brakes and it being used elsewhere. The amount of energy created is really miniscule, but better than nothing.

No, itś just the way they designed the hub. The KERS-type feature is just a piece of software that allows higher current from the alternator to the battery during deceleration.
They claim it helps fuel mileage. If the battery is low, the charging is normal. If the battery is fully charged, it is maintained at that level during deceleration.

[Z42011]

According to the technical manuals link in one of the recent posts - the front rotors are:

Aluminium floating calliper brakes or
aluminium frame calliper brakes (top models, sDrive30i, sDrive35i) are fitted on the front axle.

I was right!

See attached manual - P 19.

[bmwmick]

Originally Posted by Z42011

According to the technical manuals link in one of the recent posts - the front rotors are:

Aluminium floating calliper brakes or
aluminium frame calliper brakes (top models, sDrive30i, sDrive35i) are fitted on the front axle.

I was right!

See attached manual - P 19.

Not quite, they are describing the front caliper and yes, itś a floating caliper. The fully vented rotor is NOT a floating rotor. It has nothing to do with the KERS-type system.

btw I posted those manuals.

[teagueAMX]

Originally Posted by Z42011

According to the technical manuals link in one of the recent posts - the front rotors are:

Aluminium floating calliper brakes or
aluminium frame calliper brakes (top models, sDrive30i, sDrive35i) are fitted on the front axle.

I was right!

See attached manual - P 19.

As HerrK and bmwmick said, the rotors are not floating - they are fixed. Floating hub rotors have great application for racing, but not recommended for normal cars.

Below are some pics of 1) 1 pic of a one piece hub/rotor - cheapest to make, 2) 2 pics of a fixed/bolted rotor (front/back) which for discussion is the same as riveted, and then 3) 2 pics of fully floating hub rotors. It has a relatively small pins and allows for the disk itself and the hub to remain separated for heat dissipation.

[HerrK]

Originally Posted by Z42011

According to the technical manuals link in one of the recent posts - the front rotors are:

Aluminium floating calliper brakes or
aluminium frame calliper brakes (top models, sDrive30i, sDrive35i) are fitted on the front axle.

I was right!

See attached manual - P 19.

Actually you are wrong and you don't understand the basics of disc brakes.

As I and others have tried to explain the rotors are not floating. Yes, the calipers are floating. That is the common design for most mass produced automotive disc brake systems. Fixed calipers on the other hand have pistons on both sides of the rotor are more standard in high performance or racing applications.

Fixed calipers & floating rotors are usually synonymous in the same way as floating calipers and fixed rotors. Although sometimes they are mixed.

BMW's statement is kinda like bragging they supply their cars with nitrogen inflated pneumatic tires. Sounds high tech no?

Marketing 101. If you can't baffle em with brilliance, befuddle them with bullshit. Sorry for your befuddlement.