Sorry for the confusion on lateral versus longitudinal, was just trying to help illustrate the difference between the street/race tire. As Krazik said the slip angles and longitudinal slip percentages of a tire are related.

This is in regards to the AP dual port proportioning valve I had mentioned earlier. I'd still like to be able to tune bias for wet weather conditions and this seems to be the best option while maintaining ABS and oem pedals. Unfortunately the knee point is not quite the same as our OE prop valve. Here is an overlay of the stock prop valve versus the AP. I've emailed Ap to see if they can tune a custom valve to more closely match the stock knee point.



Andrew

 

Gotcha. Your point is much clearer now, haha. Sorry for throwing a wrench into the discussion.

 

Because, especially in gravel, but also in deep snow and sand and similar conditions, the energy dissipation of the unmoving tire dragging through the gravel is bigger than the energy dissipation of the brakes given the very low available grip levels.

 

[QUOTE=ZDan,Sep 25 2009, 06:02 AM] 1.

 

 

abs doesn't work when you're sideways no way to get the wheel moving again.

Also why abs sucks on snow and gravel in many cases. There isn't enuf friction to get the wheel moving again.

-Ry

 

So that's why my laptimes are so slow!

 

I believe ZDan was saying something similar to my comment earlier about going off tangent to the turn rather than arcing back into traffic. This can occur in a turn after loosing the car (while trying to save it) and pegging the ABS. Ideally, if you know you've lost the car you should be straightening the wheel and going off in control. However, if you are mid-turn and find yourself ABS-ing and steering at the same time, the wheels will not lock up and you will continue in the steering arc and back into traffic. The ability to brake and steer at the same time for accident avoidance is the big selling point of ABS in cars.

 

If your car is completely sideways and you have no forward velocity (referenced to the car itself) than ABS is not doing anything.

 

What tinkfist said. I probably shouldn't have said "*totally* lose it".

Anyway, add a 3rd reason why I personally prefer not to have it: It takes a very reliable and simple hydraulic system (m.c., lines, calipers) and adds wheelspeed sensors and electromechanical valving controlled by a computer. This adds multiple dditional failure modes, including the computer not knowing what the hell is going on under track conditions and going into a totally inappropriate mode of operation. A guy totalled his Audi going off turn 5 at Mosport with my club (COMSCC) a few years back because the ABS got confused and took away 99% of his braking. There have been other ABS-induced track incidents over the years as well.

But anyway, even throwing out both the argument about not having full authority to lock the wheels in the event of loss of control, and the above argument about failure modes and poor computer judgement, the other reason I prefer not to have it is enough for *me*. Modulating the brakes for myself is a skill I prefer to keep in practice.

In *my* 2001 S2000 at least, the brake bias is totally fine (fronts lock first) without ABS. I know that some other cars do have this issue and are pretty much undriveable without the ABS (stupid and unecessary to set up the system that way, not failsafe).