How does ABS work?

#21

Seriously…its usually a sub $50 fix and a little effort. Have fun racing both of the cars in GTS 1.

#22

Bottom the line up front. I think that the way our bias valve works will defeat any attempt to balance braking with dissimilar pads.

I had originally assumed that our brake bias functioned like an adjustable valve, but in a fixed position. Like maybe our rear brakes have a constant 50% braking power or something. So all I needed was rear pads with a bit more bite and I’d end up with rear pads that did 60% (for example) of the work. But that’s not how it works. The rear bias valve is an on/off switch. At a certain level of brake pressure, the valve closes and no additional pressure is allowed.

Based on brake pad wear I’d say that the rear bias valve closes at around 25% of brake pressure. That is very different from an adjustable bias where the rear brakes could get a percentage of whatever the pedal pressure is.

In that example lets say that because of weight transfer 50% rear braking power would be ideal. So we’d need rear pads with twice the brake torque. Twice is a lot.

There’s another problem tho. Lets say we do have a rear pad with twice the brake torque. Widely varying brake pads, with the rear pads maxing out at 25% is likely to cause some weird weight transfer issues. The car’s “set” would change a lot because the braking torque would have to transition from heavy rear to (once the valve closes) low rear. And nothing good would come of more braking in the rear then front.

I’ve tested a lot of brake pad combos and I’d have to say that the results are inconclusive. Which, if the bias valve closes at 25%, makes sense. If my rear pads have 10% more bite, but pedal pressure to them peaks at only 25%, then the high bite rear pad isn’t going to contribute much to stopping power.

#23

Read this.

#24

My old ITS car did not have ABS per the ITS Rules but it did have a proportioning valve. My personal experience is that I could stop the ITS car better and control it better then the Spec E30. Now I did also have slightly stickier tires Kumho V710. I also did not have much of a problem in the rain. When I first got into the Spec E30 it felt like it was never going to stop. The pedal would resist my increased threshold and it would latterly scare the $#it out of me. I have now become more accustom to the ABS brakes and have been able to adjust my threshold to suit them. The stock ABS system is old to say the least and on the newer cars is much better. Also, some of the fast guys with the newer cars also program their ABS computers for the racing environment.

My vote is a well balanced braking system can perform as good and maybe better than an older ABS system.

Also keep in mind that Simon is a lot faster than I and if he says ABS for him then that is what I am going to do as well. AND, you have to keep it per the rules.

A note about that ABS relay. You can soder some leads on board on the relay and use a replaceable fuse that you can just replace as you need to. If you weld on the car and forget to remove the relay it will be blown.

Michael
Great Lakes Region
#36

#25

sorry to hijack the thread, but What size fuse would you use on that relay?

#26

I think I used a 7.5 but you can look at the old one and what size it is. It is soldered to the board. I am sure there are other treands on this forum about it.

Michael