Trackspeed Engineering Front BBK - Group Buy
#42
... (in the rain, your rear tires do more work braking vs in the dry due to the lack of weight transfer). The FM valve would be BETTER than the OEM valve in the wet.
3 parameters describe these 2 lines:
1) slope of first line
2) slope of 2nd line
3) location of knee
An adjustable prop valve only adjusts 1 parameter, the knee location. In theory you can adjust the other 2 parameters by diddling the front and rear brake pad friction coefficients.
The ideal curve is a function of car's weight distribution, wheelbase, and CG height. Note that the tire's grip does NOT affect the shape of the ideal curve.
With the ideal curve, you always get the right proportioning regardless of surface, from ice, to race tires on hot concrete. Front and rear will lock up at the same time.
The problem is when you use a prop valve which is a 2-segment approximation. As you can see there are only 2 points where the prop valve is exactly correct, where it touches the ideal curve. Everything else is a compromise. What part do you compromise? Hot concrete? Rain on shitty tires? Snow?
It is possible that for a given adjustable prop valve, which only has one adjuster (and not 3), that the slopes are wrong, and so you would have to adjust the **** for different levels of grip. And it is possible that for one setup, rain required the **** turned down, and on another, it requires the **** turned up.
Here's a long discussion. Pay special attention to the posts by Jon H:
[NA] Brake proportioning math - MX-5 Miata Forum
#48
Hustler, with Cobalt GT's (high c.f.) front and rear my car is slightly unstable braking hard from 100 -> 50 (or so) entering turn 14 at Thunderhill.
On the street Cobalt GT's front and rear will easily induce oversteer in trail braking.
My conclusion is that I don't need more rear bias with the stock brakes, if I use high cf pads front and rear.
BTW in the MF thread, I explained why increasing the c.f. of both front and rear increases rear bias.
With stockish front and rear pads, yes, it needs more rear bias.
On the street Cobalt GT's front and rear will easily induce oversteer in trail braking.
My conclusion is that I don't need more rear bias with the stock brakes, if I use high cf pads front and rear.
BTW in the MF thread, I explained why increasing the c.f. of both front and rear increases rear bias.
With stockish front and rear pads, yes, it needs more rear bias.
Last edited by JasonC SBB; 10-20-2009 at 11:12 PM.
#49
Here are the Dynalite calipers
Wilwood Engineering - Forged Billet Dynalite Caliper
Can someone measure the approximate distance from the spindle to the middle of the pad on the Corrado rotors?
Wilwood Engineering - Forged Billet Dynalite Caliper
Can someone measure the approximate distance from the spindle to the middle of the pad on the Corrado rotors?
#50
I eyeballed my '00 brakes. Radius from spindle to center of pad appears to be 3.9".
Because the Corrado rotors are 1" larger in diameter, I will assume their radius is 4.4", or about 13% more. So the piston area of the Dynalites will need to be 11% smaller to maintain the bias.
If the 94-00 stock piston dia is 2.00", then the dynalites would have to be 1.33".
The 1.38" dynalites would have 10% more front braking than stock.
The 1.25" dynalites would have 12% less than stock. This may be a good choice for those that want more rear bias.
I would go with the latter, then fine tune the bias with the rear pads. Because the front pads need to be more aggressive anyway than the rears, this may be perfect, by using a milder rear pad.
Because the Corrado rotors are 1" larger in diameter, I will assume their radius is 4.4", or about 13% more. So the piston area of the Dynalites will need to be 11% smaller to maintain the bias.
If the 94-00 stock piston dia is 2.00", then the dynalites would have to be 1.33".
The 1.38" dynalites would have 10% more front braking than stock.
The 1.25" dynalites would have 12% less than stock. This may be a good choice for those that want more rear bias.
I would go with the latter, then fine tune the bias with the rear pads. Because the front pads need to be more aggressive anyway than the rears, this may be perfect, by using a milder rear pad.
#52
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It's not that simple. The prop valve is a 2-line segment approximation of a sideways-hyperbolic-looking curve.
The ideal curve is a function of car's weight distribution, wheelbase, and CG height. Note that the tire's grip does NOT affect the shape of the ideal curve.
With the ideal curve, you always get the right proportioning regardless of surface, from ice, to race tires on hot concrete. Front and rear will lock up at the same time.
The ideal curve is a function of car's weight distribution, wheelbase, and CG height. Note that the tire's grip does NOT affect the shape of the ideal curve.
With the ideal curve, you always get the right proportioning regardless of surface, from ice, to race tires on hot concrete. Front and rear will lock up at the same time.
The problem is when you use a prop valve which is a 2-segment approximation. As you can see there are only 2 points where the prop valve is exactly correct, where it touches the ideal curve. Everything else is a compromise. What part do you compromise? Hot concrete? Rain on shitty tires? Snow?
At the end of the day, there's also empirical evidence. I've used XP12/10s in stock brakes and the fronts lock first. I've used XP10/10s, and the fronts lock first - to the point where I can apply so much pedal force that the backing plates warp, and the rear tires never lock. This is all on stock 1.8 brakes with a stock proportioning valve.
Also - Wilwood doesn't make a 1.25" piston Dynalite. They claim in their description of the caliper that they make a 1.12, but I can't find it for a .81 rotor width. They make a 1" caliper, but it's a totally different caliper with different mounts, and only for a 1.25" wide rotor.
Carbotech does make an XP12 for the Dynalite, yes - I am using XP12s front and rear right now. I used to run 10s in the rear, but switched to 12s because the friction coefficient is higher, which provides more rear bias and keeps the bias **** from needing to be set fully in.
Last edited by Savington; 10-21-2009 at 03:01 AM.
#54
From the FM kit - I assume you are using the same?
Bore size: 1.38" (35,1 mm)
Disc width: .81" (20,6mm)
Wilwood Engineering - Forged Billet Dynalite Caliper
Wilwood #120-6806
Disc width: .81" (20,6mm)
Wilwood Engineering - Forged Billet Dynalite Caliper
#56
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One of our first buyers backed out, so I have ONE kit available at the $550 price. Send your Paypal address and shipping address to sales@trackspeedengineering.com and I will reply with a shipping quote and total.
#57
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One of our first buyers backed out, so I have ONE kit available at the $550 price. Send your Paypal address and shipping address to sales@trackspeedengineering.com and I will reply with a shipping quote and total.
Die of aids, high-pressure salesman.