anyone like racing with ABS?
03-13-2013, 04:59 PM
#22
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The first SCCA race is this weekend, so no time to dial in a new system. Hopefully GP3 will read this and keep out of my way!
The explanation of the new "electric brake distribution/proportioning system" does give me some insight as to what is going on. Apparently, you have to begin to lock the fronts before rears gain more bias... which accounts for the "always hard pedal" feel when deep in the brake zone.
That also explains why it merely locks the fronts when the abs fuse is pulled.
I will add a prop valve to the fronts after this weekends venue...I'll pull off the #'s and add plates for some street driving test-n-tune.
Thanks for the help, education and advise! cj
The explanation of the new "electric brake distribution/proportioning system" does give me some insight as to what is going on. Apparently, you have to begin to lock the fronts before rears gain more bias... which accounts for the "always hard pedal" feel when deep in the brake zone.
That also explains why it merely locks the fronts when the abs fuse is pulled.
I will add a prop valve to the fronts after this weekends venue...I'll pull off the #'s and add plates for some street driving test-n-tune.
Thanks for the help, education and advise! cj
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03-13-2013, 06:37 PM
#23
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Wrong, wrong, wrong.
I posted this in your last prop valve thread - read it again.
I posted this in your last prop valve thread - read it again.
It's a little counterintuitive, so you need to forget everything you think you know about how a bias valve works before reading this explanation. 
The ideal braking pressure applied to the front and rear calipers is a non-linear curve. As you start braking, both axles (front/rear) support approximately the same weight, so both can support the same brake pressure. As the car stops harder and harder, more of the weight shifts to the front of the car, which requires the rear brakes to do less (and require less pressure). If taken to the extreme, you end up with a car standing up on its front tires only, with the rear brakes requiring no pressure at all.
The ideal curve is the blue line, and the brake pressure applied to the REAR brakes is the white line. You can see the "knee" point - it's the poiint at which the bias valve begins to restrict the rear line pressure. The area under the ideal curve is where the front tires lock first, and the area above the ideal curve is where the rear tires lock first.
As you turn the **** on the bias valve in, it pushes the knee point further up, and therefore closer and closer to the ideal curve, which optimizes the balance between the front and rear brakes.
The stock bias valve does the same thing - the Wilwood valve just allows you to adjust that knee point and get it much closer to the ideal curve.
Remember that when you adjust the valve, you don't ever want to go above the ideal - if you're in a hard braking zone and you go over a small bump which reduces rear grip and ends up locking the tires, you'll spin the car. I will typically run a lot of rear bias on smooth tracks with very little trailbraking, and dial the bias back a bit on bumpy tracks with long, sweeping braking zones.
On race tires with our 11.75" kit in the front and 10.9" Sport rotors in the rear, I typically suggest starting at 5-6 turns from fully in, and then adding more rear bias to taste. On street tires, you'll want to run more rear bias than that, but exactly how much will depend on your application, pavement, etc.
The ideal braking pressure applied to the front and rear calipers is a non-linear curve. As you start braking, both axles (front/rear) support approximately the same weight, so both can support the same brake pressure. As the car stops harder and harder, more of the weight shifts to the front of the car, which requires the rear brakes to do less (and require less pressure). If taken to the extreme, you end up with a car standing up on its front tires only, with the rear brakes requiring no pressure at all.
The ideal curve is the blue line, and the brake pressure applied to the REAR brakes is the white line. You can see the "knee" point - it's the poiint at which the bias valve begins to restrict the rear line pressure. The area under the ideal curve is where the front tires lock first, and the area above the ideal curve is where the rear tires lock first.
As you turn the **** on the bias valve in, it pushes the knee point further up, and therefore closer and closer to the ideal curve, which optimizes the balance between the front and rear brakes.
The stock bias valve does the same thing - the Wilwood valve just allows you to adjust that knee point and get it much closer to the ideal curve.
Remember that when you adjust the valve, you don't ever want to go above the ideal - if you're in a hard braking zone and you go over a small bump which reduces rear grip and ends up locking the tires, you'll spin the car. I will typically run a lot of rear bias on smooth tracks with very little trailbraking, and dial the bias back a bit on bumpy tracks with long, sweeping braking zones.
On race tires with our 11.75" kit in the front and 10.9" Sport rotors in the rear, I typically suggest starting at 5-6 turns from fully in, and then adding more rear bias to taste. On street tires, you'll want to run more rear bias than that, but exactly how much will depend on your application, pavement, etc.
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03-13-2013, 08:01 PM
#24
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Check out EBD discussion on a tech forum where a bunch of pros hang out:
How do EBD algorithms work? - The AUTOSPORT Bulletin Board
How do EBD algorithms work? - The AUTOSPORT Bulletin Board
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03-13-2013, 08:21 PM
#25
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Also, the reference to the EBD thread was also quite informative.
Actually, what I didn't get when you explained this to me the first time was about the "replacement of the stock prop valve with the adjustable one". My car doesn't seem to have a prop valve at all. That thing on the firewall that looks like a prop valve is hollow; and is referred to in the parts manual as a "pipe joint".
I'll certainly try the prop valve fix that you've recommended. It looks like I'll need a little more supervision than the next.
Last edited by gtred; 03-13-2013 at 09:34 PM.
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