Help with Brake Bias Front to Rear VX220T
Discussion
If you have technical knowledge of brakes, perhaps you can help. I'd like to understand my brakes before upgrading them.
My VX220T suffers more pad wear at the rear than at the front. Why?
Other things I have noticed are that the rears get much more brake dust than the fronts and that the rears will boil their fluid first.
The front calipers are two piston while the rears are single piston, there is 3x as much piston area at the front of the car so I would expect 3x the force to be applied at the front. According to Vauxhall there is no proportioning valve in the system. Disc diameters are the same front to rear. Wheel diameters and therefore speeds are the same F-R. Pad areas are similar F-R.
Most people tell me it's down to tyre size and weight distribution but I don't buy that. Tyre size is irrelevant since none of them lose traction. Weight distribution is irrelevant since front and rear are joined by a solid body. I agree that as a brake system designer you would put more brake force at the end with most of the weight and grip, but you would do it by increasing the piston diameter. The bit I don't believe is that the greater the weight over an axle, the more braking that end of the car will do.
Accelera Comigo
My VX220T suffers more pad wear at the rear than at the front. Why?
Other things I have noticed are that the rears get much more brake dust than the fronts and that the rears will boil their fluid first.
The front calipers are two piston while the rears are single piston, there is 3x as much piston area at the front of the car so I would expect 3x the force to be applied at the front. According to Vauxhall there is no proportioning valve in the system. Disc diameters are the same front to rear. Wheel diameters and therefore speeds are the same F-R. Pad areas are similar F-R.
Most people tell me it's down to tyre size and weight distribution but I don't buy that. Tyre size is irrelevant since none of them lose traction. Weight distribution is irrelevant since front and rear are joined by a solid body. I agree that as a brake system designer you would put more brake force at the end with most of the weight and grip, but you would do it by increasing the piston diameter. The bit I don't believe is that the greater the weight over an axle, the more braking that end of the car will do.
Accelera Comigo
What is the pad area like front/rear? It's common to put much smaller pads on the rear. What size discs front/rear? A smaller disc will produce less braking effect for the same line force on the pads. Do you have single master cylinder, tandem dual master cylinder, parallel master etc? Do the rear brakes get hot in gentle driving? This could indicate that they are dragging slightly.
The rear pads could well be a softer compound. Its a good way of fine-tuning the braking effort at each end whilst still keeping "standard" sized discs & callipers that you use on something else rather than getting "specials" made.
I'd certainly expect your rear brakes to do more than those on a front engine front drive hatchback, which would be very light on the back anyway.
I'd certainly expect your rear brakes to do more than those on a front engine front drive hatchback, which would be very light on the back anyway.
GreenV8S - most answers are in my original post. I reckon the master cylinder is irrelevant because the same pressure is supplied to each corner, however you plumb the lines. I wondered about the rears dragging too but they don't, there is no residual binding of the calipers because you can always push the car by hand.
Avocet - good point but sorry, I use Ferodo 2500 at both ends.
Thanks guys, any more suggestions??
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Good point, I should have read more carefully.
It is almost certain that your car does have a brake bias valve. It would be very dangerous without one and I don't see how they would have got type approval. This would affect the dynamic balance i.e. under heavy braking however it would not affect the static bias i.e. under very light braking.
If you have a tandem master cylinder, or dual master cylinder with balance bar, then the front and rear circuits are hydraulically separate and need not run at the same line pressure.
It is almost certain that your car does have a brake bias valve. It would be very dangerous without one and I don't see how they would have got type approval. This would affect the dynamic balance i.e. under heavy braking however it would not affect the static bias i.e. under very light braking.
If you have a tandem master cylinder, or dual master cylinder with balance bar, then the front and rear circuits are hydraulically separate and need not run at the same line pressure.
GreenV8S said:
Good point, I should have read more carefully.
It is almost certain that your car does have a brake bias valve. It would be very dangerous without one and I don't see how they would have got type approval. This would affect the dynamic balance i.e. under heavy braking however it would not affect the static bias i.e. under very light braking.
If you have a tandem master cylinder, or dual master cylinder with balance bar, then the front and rear circuits are hydraulically separate and need not run at the same line pressure.
Agree with Peter that the balance could be integrated in the brake master cylinder design. Especially with this type of car as often it would/could be used as a track car, you could expect for example an adjustable balance bar. This would be the first area I would investigate to be sure.
Rob
Interesting, thanks for your thoughts.
I guess the ultimate test is to put a pressure gauge at each end a press the pedal. Mmmm.
I'll have a poke around with the master cylinder I think. There is an AP Racing kit sold for the car at www.vx220.org.uk forum which I know AP Racing had a hand in designing. The kit only replaces the fronts and doesn't require you to make any system modifications so I wanted to understand what else was in the system.
Accelera Comigo
I guess the ultimate test is to put a pressure gauge at each end a press the pedal. Mmmm.
I'll have a poke around with the master cylinder I think. There is an AP Racing kit sold for the car at www.vx220.org.uk forum which I know AP Racing had a hand in designing. The kit only replaces the fronts and doesn't require you to make any system modifications so I wanted to understand what else was in the system.
Accelera Comigo
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