Bill Verburg

From '84 M491 used a p/v.
yes you can safely remove it to get the bias curves that 930 have. There will still be more front bias than any 911 thru '84 had.

Bill Verburg

Weight transfer does not depend on spring rates

It only correlates directly to acceleration rate, height of center of mass and total mass and inversely to wheelbase

In the wet negative acceleration is less so there is less weight transfer so more rear bias can be used

-nick

Yes, springs effect body roll/pitch and not weight transfer. I should be beaten with a mechanics book for that one!

Lowering the ride height is the influencing change. Though I don't know how much change in weight transfer the typical 1" height decrease makes.

Mezger

Maybe someone wants to enlighten me.
My 90 C2 with the 2 piston rears has in my opinion absolutely insufficient rear axle brake power.
My questions are as follows:
1. Will the 4 piston setup change my bias for the better
2. If staying with the two piston setup, what is the best way to go?

Thanks rennlister friends!

alexjc4

2 pot rears have more "power" than 4 pot rears (as in more rear bias)

However the 2 pot rears are limited by their thermal capacity which will show up in rear tough conditions, on track etc. You may find you boil the brake fluid or you may just consume the rear pads more quickly. You could try and fit the best brake fluid you can afford and some pads that can handle the heat and see how you go. Depends on your usage though.

If you genuinely just want more rear bias/"power" in the rear brakes you can take the proportioning valve out and stay with the 2 pot C2 rears. But C4 rears will reduce the rear bias and thereby reduce rear axle brake "power".

Mezger

Hello Alex,

Thanks for your quick response.
According to what you just wrote the "best" setup would be utilization of C4 calipers without use of the rear proportioning valve, right?

alexjc4

Yes, that would give you more rear bias and more thermal capacity. Brake bias is a matter of taste though, I know people that have tracked their cars heavily with C4 rears and the p/v still in place and been very happy.

anto1150

Best upgrade would be 993 rear calipers and swap the rear PV with a Tilton adjustable one.
As a general rule: the more the grip (dry track and sticky tyres), the less rear bias; as opposite, on road and less grippy conditions you need more rear byte.
If you change suspensions setup, harder suspensions call for more rear bias; softer setups need less rear brake.

Ciao