Re: Changing bias works both ways.
#1092497 - 11/03/05 02:35 PM
Originally posted by DemonSVT:
What's horrible is people only doing fronts. That throws off the bias and the overall balance of the car tremendously. Why is it nobody is harping on them for destroying the stock bias or it being dangerous because of it?
If you want to get technical even just changing the front pads to an aggressive mix changes the bias.
That's not completely correct. You're assuming the fit of a front kit will grossly over bias the front brakes. I'll agree that pairing a front and rear of specific sizing has its benefits.
Yes pads alone can alter the % by more than most folks think. But adding front bias is in no way going to be "dangerous".
In the spirit of the often quoted ST wite pages....adding some rear bias can often improve the cars total braking performance. *Note however that not all their kits really do that as I was chuckling a bit at one of them recently on a platform cited to be such- it's not. Anyhow...when you consider that most folks take 'braking improvements' to mean both firmer pedal (wrongly assumed) and high speed braking you are actually speaking of dynamic braking, not the common reference to static bias.
Using some simple numbers like 75/25 (not uncommon on a FWD car) you'd assume that making this 65/35 would be far better. And in some slow speed cases you'd be right. However under high speed stops where weight shif is greater you'd be over working the fronts. They still do the job but take far more pressure input to get the job done. Assuming you might pull 1.2G under hard braking you might want to consider 77/23 for example. Where the fronts keep pace with the required braking.
My point is that you can't really over brake the front of the car and be dangerous. Within some common sense levels at least. I'm not suggesting one massive front kit with no rears.
For the most part the TCE white pages subscribe to the simple theory of 'larger rotor, less piston area, tune with pad'. This formula permits the fronts attain torque with leverage, firm up the pedal, and require a bit more input pressure to keep pace. The pad selection can then ramp up the required front torque to keep pace with the weight shift. By my notes the Contour requires nearly identical leg pressure on a 13"/6pot as the stock brakes. And the bias is within 2.5% of stock. Under hard braking however when fit with good pads; the stock brakes require 80# of leg where the above kit requires only 60# to achieve the same rotor torque. In this case the rear line pressure on the stock brakes is 541psi, the 13" kit has a rear line pressure of only 406. Depending upon the knee point of the stock prop valve the stock parts are probably shut down completely and the BBK still keeping modest pressure to compliment the front kit. Which one do you think is going to provide a more stable brake platform?
Let's consider the 'bigger is better rear' proposal. For fun: Front- stock caliper on 12" rotor Rear- 2.125 piston on 11" rotor Both with off the shelf .40Cf pads
How about a 61/39 bias? Not for me thank you. You'd need a good prop valve to reduce this rear bias as you mentioned. In fact, if my program is correct you'll have to drop the 541psi input down to a lowly 125psi to get to the same torque value as the 13" example with the race pads. Seeing that the valve allows for a max of about 50% you won't get there.....With half you'll net 77% front bias- still more than you'd be able to use under hard braking I suspect. So what do you do? Add mega front pads to the car. Fit a .55Cf pad to the stock caliper and you'll be at 84% again. Not bad, but like all the other kits you'll be right back to the rears being along for the ride! With full reduction at the valve. Go back to lower pressures and street use with this and you're at 68/32.
I'm not going to say you cannot make some of this work for you. But you're going to find the needs of static and dynamic braking moments are going to play hell with the idea. The idea of the prop valve is to tune it to conditions not use it as a driver aide every time you pull out of the driveway. And with much larger rear calipers we never got to pedal feel. Think long and soft.
Maybe I'm just rambling too much for you but it's worth some thought at least.