change proportioning valve? Or Adjustable Brake bias
#16
So what would be the most effective way to move some of the bias to the front on the m491 some where close to the NB 3.2 cars without resorting to twin MC and no booster? Does my car have a proportion valve that I can swap with another 911 or tinker with like the 964's? I don't want to over do it cuz u can spin like a top without warning if the rears lock up first.
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.
#17
Thanks for bringing up this discussion. I'm putting it on my to-do list. Anyone with aftermarket springs/shocks is losing braking ability due to too much front bias. Less weight transfer to the front and the front tires will break loose more quickly. My wet weather braking is truly terrible.
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
#18
Three Wheelin'
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.
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.
#19
Instructor
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!
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!
#20
Three Wheelin'
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".
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".
#21
Instructor
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?
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?
#22
Three Wheelin'
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.
#23
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
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
Last edited by anto1150; 08-09-2016 at 03:13 AM.