My bug with 2.4 type 4

[evilC]

The front brakes will be 4 piston and the rear is shown as a single piston. A bug requires near to a 50/50 brake bias. That is to say that the braking power should be about the same front and rear because of the heavy rear weight bias transfers forward under braking. On a front engined car with a weight bias of 55% front and 45% rear the brake bias will be around 75% front and 25% rear to take care of the weight transfer under braking.

The way to calculate your current bias is to compare the total front caliper piston area/front master cylinder piston area with the total rear caliper piston area/rear master piston area. Also, the brake disc diameters will moderate the final figures but I am assuming that the front and rear discs are about the same diameter?

You say that the master cylinder is larger - why? The smaller the master cylinder the more power you can apply to the brakes as the hydraulic advantage = total caliper piston area/master piston area. The downside of the smaller master piston is the longer pedal travel but generally this is minimal on a well set system. The bug 19/19 master cylinder is usually big enough for almost all applications and it will be only where massive caliper piston areas are used will you need a larger master cylinder to compensate.

Clive

[RuleO9]

The diameter is the same.. You're the first to say that the brake bias isn't correct with these calipers..
So i need? Bigger rear calipers or smaller had the front?

[evilC]

You do need the same piston area or thereabouts at the front and rear if you are running a plain bore master cylinder. Alternatively, you could use a balance bar set up on the brakes so that you can run the same calipers as you have but i suspect that the difference in the master cylinder bores would be almost unobtainable. Another problem you have is that the rear disc is solid that restricts your options on calipers dramatically. You were much better off using the 944 rear disc as many of the standard Porsche alloy calipers fit. I have the 944 set up with 928S4 4 pot calipers on the rear that would complement your front set up perfectly.

I suspect the Kersher rear brakes were to match the standard disc fronts not a Porsche 4 pot units. If you want to retain some sensible brake balance you will need in my opinion to change the rear discs and calipers for a Porsche set up with 4 pot calipers. Obviously, if you can fit the same set up to the rear that you have as the front that would be ideal. I would (have) fitted a brake bias valve in the rear circuit when you have matching front and rear or more powerful rear brakes so that you can finely balance the car. For a road car the front brakes must just lock before the rear to maintain optimum control and maximum braking effort.

Clive

[Wally]

Originally Posted by evilC

The front brakes will be 4 piston and the rear is shown as a single piston. A bug requires near to a 50/50 brake bias. That is to say that the braking power should be about the same front and rear because of the heavy rear weight bias transfers forward under braking. On a front engined car with a weight bias of 55% front and 45% rear the brake bias will be around 75% front and 25% rear to take care of the weight transfer under braking.

The way to calculate your current bias is to compare the total front caliper piston area/front master cylinder piston area with the total rear caliper piston area/rear master piston area. Also, the brake disc diameters will moderate the final figures but I am assuming that the front and rear discs are about the same diameter?

You say that the master cylinder is larger - why? The smaller the master cylinder the more power you can apply to the brakes as the hydraulic advantage = total caliper piston area/master piston area. The downside of the smaller master piston is the longer pedal travel but generally this is minimal on a well set system. The bug 19/19 master cylinder is usually big enough for almost all applications and it will be only where massive caliper piston areas are used will you need a larger master cylinder to compensate.

Clive

All of the above is VERY true. Took me a while to actually get to know the real world data against the 'theory'. The theory is rather off, but the above is spot on.
Just take really good notice of what he said Roel ;-)

[RuleO9]

I can't use these rear brakes? Also with a balance bar set up on the brakes?
Because these disc and calipers are new.. and my pockets are almost empty after 2 $$$ years...
Than i have to change the discs and calipers.. An other 1000$