Brake Bias

[eyup]

Morning all,

Simply because I don't know and a quick search did not reveal the answer. What is, if there is any, the foot brake bias front/rear on the z4 coupe?

Thank you

[Ewazix]

The ABS DSC/traction modules continuously optimise braking forces, the underlying braking potential of the front with bigger discs and multiple pots probably gives a ratio of about 60/40 but in use the dynamic bias isn't fixed.

I always wonder if people are getting the best out of the system when they only upgrade their front brakes but assume serious track guys with modded set-ups will have discovered the advantages, and limits

[eyup]

Great. Thank you

[Steve84N]

All Z4s have single pot calipers.

I have felt the difference of upgrading brakes back on my old Fiesta Mk4.

- Started with 240mm solid and drums
- Changed front for 260mm vented (pretty big jump but not amazing)
- Changed rears to solid discs (definitely noticeable but drums are pants)
- Changed fronts to 280mm vented (amazing stopping power)

It was only a 1.25 with no ABS but it ended up with very good braking. You can get away with less extreme front only upgrades but improving the rear helps too.

You will probably find that your rear brakes are doing less than 30% of the braking when under load.

brakebias_5.jpg (25.83 KiB) Viewed 535 times

www.stoptech.com/technical-support/tech ... ce-matters

[Ewazix]

All Z4s have single pot calipers.

I have felt the difference of upgrading brakes back on my old Fiesta Mk4.

- Started with 240mm solid and drums
- Changed front for 260mm vented (pretty big jump but not amazing)
- Changed rears to solid discs (definitely noticeable but drums are pants)
- Changed fronts to 280mm vented (amazing stopping power)

It was only a 1.25 with no ABS but it ended up with very good braking. You can get away with less extreme front only upgrades but improving the rear helps too.

You will probably find that your rear brakes are doing less than 30% of the braking when under load.

brakebias_5.jpg

www.stoptech.com/technical-support/tech ... ce-matters

Your experience with the rear upgrades makes sense, I guess the benefit of upgrading rears with the front would be even more noticeable on the Z4 with 50/50 weight bias as opposed to a typical FWD like your Fiesta with about a 60F/40R weight distribution.

[Steve84N]

Depends how you drive it.

Having more rear braking power on a FWD is actually very noticeable if you're still on the brakes into a corner as it can give you less understeer (explained in that article above).

[rally-chris]

Differences in static weight distribution are largely irrelevant, as it’s all about weight transfer forward under braking. The rear brakes are always limited in what they can add to the overall braking as weight is transferred to the front during braking and the last thing you want is the rears locking up and causing instability in the car.

I would assume that the lower down centre of gravity and relatively stiff suspension on a sports car like a Z4 will result in less weight transfer forward than say a typical rolly polly FWD hatchback so you probably can make more use of the rear brakes before risk of locking occurs (or the ABD system reduces rear brake prsssure before this happens).

Chris

[Steve84N]

Strangely, you get more rear brake bias with less load on the rear and a higher centre of gravity.

Probably why FWD cars have smaller rear brakes as they want to keep the bias down for benign handling whereas RWD cars have bigger rear brakes relatively speaking.

[MrPT]

The E46 M3 community has put a lot of time into static bias calculations. I was trying to understand them (and mostly failed) when I upgraded my front brakes and came away with the impression that they are still useful as a reference point once you start modifying components, mixing pads etc.

The range of values being talked about for the M3 runs between about 1.5:1 and 2.25:1, so between 60/40 and 69/31 F:R. Stock is about 66/34. This is at the axle, so takes into account the whole braking system but not the tyres and their interaction with the road.

[BMWZ4MC]

Differences in static weight distribution are largely irrelevant, as it’s all about weight transfer forward under braking. The rear brakes are always limited in what they can add to the overall braking as weight is transferred to the front during braking and the last thing you want is the rears locking up and causing instability in the car.

I would assume that the lower down centre of gravity and relatively stiff suspension on a sports car like a Z4 will result in less weight transfer forward than say a typical rolly polly FWD hatchback so you probably can make more use of the rear brakes before risk of locking occurs (or the ABD system reduces rear brake prsssure before this happens).

Chris

I'll second this, as evidenced when I changed from Eibachs with OEM dampers to KW Clubsports. The reduced pitching under braking led to a marked reduction in braking distances in track driving.

[Jembo]

The ABS DSC/traction modules continuously optimise braking forces, the underlying braking potential of the front with bigger discs and multiple pots probably gives a ratio of about 60/40 but in use the dynamic bias isn't fixed.

I always wonder if people are getting the best out of the system when they only upgrade their front brakes but assume serious track guys with modded set-ups will have discovered the advantages, and limits

I experienced this on my old 3.0 when upgraded front from 300mm to 325mm

In the dry in summer, real noticeable difference though balanced.... in the winter especially when wet, if you ever really needed to slam on the anchors hard, the front ABS sometimes kicked in & you felt as if there was nothing there at the rear.

My stock //M brakes are more than adequate for me...