Originally posted by SteedaSVTââ??¢: I was thinking the Same thing, Rara and I talked about it and if you have the 13" kit the Focus FSVT rotors on the Rear seems it would be a better option. Than the 280 CSVT rotors on the rear
For looks only.
Rara knows all about braking bias. On a nose heavy FWD car the rear brakes, at best, can generate 20% of the braking force. On a stock weight distribution Contour it is more like 15%.
This does not even take into consideration to caliper piston's ability to stop the rotors. (its force output) This is the reason I went with an overly aggressive pad choice on the rears. I wanted to make the most out of what the small stock rear caliper would give me.
ANY BRAKE SETUP CHANGE, from pro-fabbed kits to economy brake pads, is much more then a simple swap fest. The devil is always in the detail work. If you don't do your homework you normally end up with poor results. There are countless "big brake" upgrade kits out there that prove that fact over and over again.
Demon, you are mostly right here. But remember, once you have upgraded the fronts, you have shifted the brake bias to the front, potentially by a significant amount, which then needs to be balanced back to stock levels to make the best use of the full brake system. There are four key ways to affect the F/R bias of a brake system, and any of them can have a significant effect, so its not a terribly simple proposal in getting it all right.
First is proportioning, or rear line pressure proportioning. Some contours have a typical prop valve which limits rear line pressure, and some are controlled electronically by the ABS.
Second, is the torque lever arm, or basically the effective radius of the rotor (note, this is not the same as the actual radius of the rotor, but it depends on pad size as well)
Third is the friction co-efficient of the linings used. This one is difficult on a street car, because good data is hard to come by on most linings.
and Fourth is also system pressure, but more related to the caliper piston sizes relative to the master cylinder size. Most kit makers try not to change this much, as it will dramatically change pedal feel as well.
So, I'll tell you guys what, if I can dig up the info I need, I'll run some bias numbers today, and post the results. However, my gut feeling says the 300/280 combo will be a little more rear biased than stock, and a 330/300 combo will be about the same as stock, all depending on what linings are used.
Also, as a side note, swept area, and pad size (within reason) don't have a lot to do with overall braking power. These factors more come in to play when you start to consider fade, and pad life, and aesthetic concerns like Stazi mentioned.
On Edit - btw, Demon, I know I addressed the first comment directly to you, but the rest of the post is informational for the general public who may not know the fundamentals of a brake system design.
