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Re: Brake Bias Posted by magalar [Email]  (#1325)  [Profile/Gallery]
(more from magalar) on Fri, 24 Oct 2014 07:50:38
In Reply to: Brake Bias, BenR, Mon, 20 Oct 2014 00:02:34 Members do not see ads below this line. - Help Keep This Site Online - Signup |
On numerous newer cars with Bosch or Teves ABS systems (newer as in post 2000...), brake bias is done via the ABS pump/module.
Wheel speed is constantly monitored via the wheel sensors. Under braking, rear wheel speed must be at least 80% of the front wheel speed. If less, then the valves in the ABS/block opens, releasing fluid pressure to the rear wheels, preventing lockup. Note that the ABS pump doesn't run, so you won't feel anything at the pedal. If speed continues to drop, then ABS function is triggered normally.
Benefits : all the hardware is already in the car. Only a software programmation is needed. No need for a suspension height proportionning valve, like on older cars. Very simple systeme indeed.
Cons : If ABS is not functionnal, no brake proportionning. You then have a fixed brake bias, as per the calipers piston area and the disc diameter. Remember, brake force is dependent of the pressure of the fluid on each piston, and of the leverage force of the pads on the discs. (all else being equal).
So for your problem : if ABS dead, repair it.
If good, install more aggressive pads at the back. Same pressure, same leverage, but more bite on the same diameter discs. If it was me, I would begin with that.
Or, you can install calipers with bigger pistons (more pressure at the rear). You can also install larger diameter rear discs, so the leverage force will be greater. Also, but more complicated, install a different master cylinder (if it exists...) with more pressure toward the rear.
But if your actual rear calipers and discs are braking strongly enough to attain the 80% wheel speed, you won't see a gain. You'll just attain it earlier and more often.
Note that rear vented discs of the same diameter won't do any good for the rear brake force, they will only be more fade resistant. That might help if the problem lies in fade, not in brake proportionning.
Hope this helps somewhat...
, Fri, 24 Oct 2014 07:50:38 <-- Viewing This Message
, Mon, 20 Oct 2014 07:31:51, Wed, 22 Oct 2014 09:57:17, Mon, 20 Oct 2014 05:17:11
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