I have a simple question, but with a potentially large impact on on braking performance on my S-type project car.

What affect will increasing, say double, the piston area of a rear brake caliper have on an Electronic Brake Control module (ABS) On paper I have a situation where the combination of the front piston area/rotor diameter gives me around 68% front brake bias. I want 52% front bias. In order to achieve this with the rear rotor size I want/need to use, I have to almost double the caliper piston area.

Doubling the piston area will increase the amount of brake fluid required to push out the caliper pistons.
Can or will an ABS module be able to bias/proportion the increased fluid flow so that the caliper activates quickly enough to balance the brakes on hard stops.

Perhaps someone has experienced this before, otherwise put on your thinking caps and let me know what you think.

 

I've got some experience in this area. Modern abs systems can cope well with considerable caliper changes. What are you trying to accomplish? I'd suggest you look at the system as a whole. Case in point...if you are increasing your rear brake bias you can offset the effects by increasing traction with a larger wheel and tire or weight relocation (relocate battery). Seems like you are looking at this staticly. You have to consider your vehicles dynamics. On most front engines vehicles...If you just increase rear bias the rears will lock early and limit braking ability becasue you wont get the proper weight shift to the front wheels... and then theY will lock and abs will intervene. I would recommed against increasing rear pistton area more than 10%, a bigger piston needs more fluid and that will result in greater peddle travel. Try to accomplish you bias goals mechanically with a larger rotor.

 

Wow! one of my older threads, finally answered. I've learned a lot since I posted the original question.

Regarding tires, The car will be fitted with 345/30-19 rears, and 285/30-19 front tires. There are 380MM rotors with 8 pot, Brembo Calipers on front, and either 365 or 380 rotors in back, with either stock STR rear brembos, or factory Camaro rear Brembos on back. I'd have to go back and look at my Spreadsheet to post piston area, and the bias calculations I ended up with. One of the problems I still have is being able to go to larger rotors in back , and be able to design caliper to Hub carrier mounting adapters. I would like to use larger rotors, but the size I need in order to allow for easily designed caliper adapters, increases the rear bias to much.

 

From what I've picked up from the JTIS download and other factory svc. publications there is no effect on the ability of the ABS system to work. This is true only within the parameters of the specifications that Jaguar has set for their individual models.

For example I'm starting the process of gathering up the various parts needed to bring my wife's '04 XJ8 up to the same brake specifications as a 2004 XJR with the Brembo set-up. AS long as what I do is done with adherence to what Jaguar originally equipped the XJR's with I don't have to fiddle with the ABS system.