Can r-compounds "fool" our anti-lock brakes?
07-10-2009, 10:21 PM
#1
2nd Gear Member
Thread Starter
Join Date: Feb 2007
Location: Texas
Posts: 162
Can r-compounds "fool" our anti-lock brakes?
I've done over 25 track days at TWS in the last two years and finally moved up to r-comps in January of this year for NASA time trials.
However, in February, we had a 30 minutes on/30 minutes off, solo only event. With that much track time (8 sessions) I tried every line I could think of for practice. And given the 25+ track days previously, I had learned a long time ago to slow down when off line. (As beginners, I'm sure we've all taken the late point-by, gone it too hot and off line, and hopefully stayed on track!) However I noticed a couple of times that the tires were locking up and the car wouldn't slow down like I expected.
So I did my first time trial in April. Open passing, but you are gridded by lap time, so there is actually not that much passing after the first or second session.
During the sessions, two times when I'm passing to the inside, and I think that I have slowed down enough, the car just doesn't seem to stop. It's like I let off the brakes or the tires were sliding.
So long story short, can r-comps "fool" the stock anti-locks where the computer thinks that the tires are sliding and so the computer releases pressure? I'm thinking that the computer thinks the tires are slowing down too fast (relative to street tires) and so thinks they are locking up and lets off the pressure.
I've never missed a corner that badly with performance street tires.
Sorry for the long post.
-Wayne
However, in February, we had a 30 minutes on/30 minutes off, solo only event. With that much track time (8 sessions) I tried every line I could think of for practice. And given the 25+ track days previously, I had learned a long time ago to slow down when off line. (As beginners, I'm sure we've all taken the late point-by, gone it too hot and off line, and hopefully stayed on track!) However I noticed a couple of times that the tires were locking up and the car wouldn't slow down like I expected.
So I did my first time trial in April. Open passing, but you are gridded by lap time, so there is actually not that much passing after the first or second session.
During the sessions, two times when I'm passing to the inside, and I think that I have slowed down enough, the car just doesn't seem to stop. It's like I let off the brakes or the tires were sliding.
So long story short, can r-comps "fool" the stock anti-locks where the computer thinks that the tires are sliding and so the computer releases pressure? I'm thinking that the computer thinks the tires are slowing down too fast (relative to street tires) and so thinks they are locking up and lets off the pressure.
I've never missed a corner that badly with performance street tires.
Sorry for the long post.
-Wayne
07-10-2009, 10:45 PM
#2
5th Gear Member
Join Date: Jul 2007
Location: TX
Posts: 4,897
That's a very interesting observation because I've noticed odd behavior on many of my former anti-lock equipped vehicles once going to larger, stickier tires and notice it on my current car.
I always attributed it to heat-soak as it occurs less in the colder months but larger/stickier tires exascerbate it for sure. More rolling resistance?
Can the computer relate rolling resistance?
I always attributed it to heat-soak as it occurs less in the colder months but larger/stickier tires exascerbate it for sure. More rolling resistance?
Can the computer relate rolling resistance?
07-11-2009, 11:10 PM
#4
1st Gear Member
Join Date: Jun 2008
Posts: 114
The short answer is no. Even with slicks, you can feel the abs engage and it's a pulsing not just bleeding brake pressure. You should also understand that slicks will be much harder on your brake setup. Don't forget that in addition to better cornering traction, you're also going to have even more traction available for braking. To me, your issue sounds like brake fade.
Good luck,
Edward
BTW, have you had any of the NASA racers take your car for a spin and offer any advice. Keep an eye out for Wayne Manor. He's ridden with me several times when I was tracking my Lightning and he's a wealth of info and advice.
Good luck,
Edward
BTW, have you had any of the NASA racers take your car for a spin and offer any advice. Keep an eye out for Wayne Manor. He's ridden with me several times when I was tracking my Lightning and he's a wealth of info and advice.
07-13-2009, 09:06 AM
#7
6th Gear Member
Join Date: Feb 2007
Location: state of confusion
Posts: 7,635
So long story short, can r-comps "fool" the stock anti-locks where the computer thinks that the tires are sliding and so the computer releases pressure? I'm thinking that the computer thinks the tires are slowing down too fast (relative to street tires) and so thinks they are locking up and lets off the pressure.
I suppose that it's theoretically possible to program a maximum deceleration into the ABS logic. But I would expect that such a limitation would be higher than that available with R-comp capability.
FWIW, I have experienced "unexpected ABS actuation" a couple of times on the OE 235/50-18's on what visibly appeared to be smooth, dry, clean asphalt. For that and a couple of other reasons I'm still not 100.00% sold on ABS.
Norm
07-13-2009, 06:46 PM
#8
Former Sponsor
Join Date: Sep 2007
Posts: 1,936
ABS has no idea what tires are on the car. It only sees individual wheel speed....
My guess: You were on the dirty line, which had crap for grip and you were skating around on the clag. Slicks (which basically R-comps are) have no grooves or biting edges to help with grip on sand, grit, etc. When you really get too far into ABS, you run into the "ice-mode" program. Basically there are parameters that makes the computer think you are on a slick surface like ice, and generally you are then limited to about a .3g stopping force as the assumption is it's really slick. When this happens you get a very high, hard, and quickly cycling pedal. Is that what you had?
My guess: You were on the dirty line, which had crap for grip and you were skating around on the clag. Slicks (which basically R-comps are) have no grooves or biting edges to help with grip on sand, grit, etc. When you really get too far into ABS, you run into the "ice-mode" program. Basically there are parameters that makes the computer think you are on a slick surface like ice, and generally you are then limited to about a .3g stopping force as the assumption is it's really slick. When this happens you get a very high, hard, and quickly cycling pedal. Is that what you had?
07-13-2009, 08:06 PM
#9
2nd Gear Member
Thread Starter
Join Date: Feb 2007
Location: Texas
Posts: 162
ABS has no idea what tires are on the car. It only sees individual wheel speed....
My guess: You were on the dirty line, which had crap for grip and you were skating around on the clag. Slicks (which basically R-comps are) have no grooves or biting edges to help with grip on sand, grit, etc. When you really get too far into ABS, you run into the "ice-mode" program. Basically there are parameters that makes the computer think you are on a slick surface like ice, and generally you are then limited to about a .3g stopping force as the assumption is it's really slick. When this happens you get a very high, hard, and quickly cycling pedal. Is that what you had?
My guess: You were on the dirty line, which had crap for grip and you were skating around on the clag. Slicks (which basically R-comps are) have no grooves or biting edges to help with grip on sand, grit, etc. When you really get too far into ABS, you run into the "ice-mode" program. Basically there are parameters that makes the computer think you are on a slick surface like ice, and generally you are then limited to about a .3g stopping force as the assumption is it's really slick. When this happens you get a very high, hard, and quickly cycling pedal. Is that what you had?
