gt3skea

anyone ever have it go off (abs error come up up in the communication screen and abs light come on) the second you step on the brake at a track event? for me- 3rd lap, not even full out, stood on the brake and all hell broke loose. unfortunately im not a good enough driver at 155 (roebling front strectch T1) to handle as well as i would have liked, but i avoided catastrophe.

i hope none of you have but i thought i would check here, it nearly cost me my car - im waiting to hear back on the why i got the brake (abs) light coming on at the worst possible time - prelim idea is that i have a faulty abs sensor.

and the second question would be regarding no abs. i have driven the skippy cars without it and practiced threshold braking, and a slight release would let the wheels start to roll again - but would not happen here? to fast? unfortunately at times i rely on it, but lucky this happened here instead of last time at track racing Road ATL.

thanks in advance for any idea's...

MetalSolid

The GT3 brakes are designed to go into severe front bias (front wheels lock first) in the event there's a problem [ABS light].

roberga

I had it come onn and had no power assist. I came up to a light and when I applied the brakes nothing, I then applied more pressure and ended up sking into the intersection with a cloud of tire smoke around the car. I flat spotted the fronts. 3 brakes are computer controlled and if that light is on the best thing to do is stop turn the car off and back on. If it is a simple fault it will reset.
This can happen if pulling out at an angle to avoid splitter damage and applying the brake with one of the front wheels off the ground. The computer sees this as a fault.
It has happened to me maybe 4 or 5 times when leaving a service station and pulling on to a surface road were there is a big transition.

Greg Fishman

On the 993's many racers installed a switched to cycle the ABS. Autometrics sold a kit, they might have one for the GT3.

GT3 Nut

gt3skea: I have had this happen to me on track at a very bad time as well almost 2 years ago. I ended up in the tire wall!
It was caused by the tires being incorrect for the car - way too much difference in height between front and rear. The tires were recommended to me by a reputable place but they apparently didn't know better. I was trying the Michelin slicks that are commonly used on the Cup cars in Europe. It was an expensive mistake.
After putting the proper tires on - no problems with ABS for me.

Z06

What tires where you using?

I had this happen with the Kumho V710 245, diameter-24.8" + 315-D=26.4"
For me it was only front brakes in full abs mode, like it was on ice... still manged some good lap times.

Larry Herman

I always ran the same diameter tire, front and rear, in street, R compound and race tires. I have triggered the ABS many times due to rough or slippery surfaces or sometimes just too much brakes. I never have had the "lockout" problems that you are discussing, if that info helps you at all.

gt3skea

i have hoosiers - 245 in front and 305 in the rear - i have used that tire probably 50+ heat cycles and never had an issue.

i raced this car with the exact set up 2 weeks ago at the pca race, the only difference was slightly different tow and neg camber, a cup car style extinguisher system... it was the first turn on the 3rd lap of the weekend. i ended up on top of a dirt hilland ran over a few small trees.

and thank you greg - i will call autometrics...

now i had more rake put in the car before the race a few weeks ago - so i almost want to believe it had something to do with the ride height difference, but again it raced fine - and this was only the 3rd lap of a de i only went to so i could help my wife get used to the track.

Phokaioglaukos

OEM sizes are 235/40 and 295/30. I had planned to switch to Toyo RA-1s next week, and they are not available in those sizes. They do have 245/40 and 275/35 for the fronts and 305/35 and 335/30 for the rears. There is a nifty tire size calculator at Calculator , and when I plug those numbers in I get the following Diameter differences from the OEM sizes:

245--1.21%
275 --.67%
305--5.46%
335--3.67%

The web site suggests a 3% difference may be too much. Looks like 275s and 335s, which NJ-GT has mananged to fit, MAY be ok, but I find it hard to imagine that they will fit my car. My 235s rub at full lock as it is. the 245s should be good, but I guess the 305s are not a good idea!

What do do?

Matt, what size tires caused your issue? I wonder what plugging those sizes would show in percentage variation....

Phokaioglaukos

Are these the 245/35 and 305/30 Hoosier Sports Car Radial Wet tires? If so, the 245s are off by 2.56% and the 305s are off by only .96%. The 225/40s would have been off by only 1.26%. That might be a better front tire.

I wonder if the ABS issue is a concern with the fronts and the backs being off OEM sizes or off front to back. I would guess the latter so that if both fronts and backs were off 3% from OEM that there would not be an issue, except that the speedometer would nor read correctly.

I also wonder how great a difference front to back is necessary to trigger the problem.

Z06

It sounds like it's the ABS system that failed and not something you did or changed, maybe a sensor. Take it to the dealer.

Terry L

There is a very active current thread on the same subject on Elisetalk, the Lotus board, where the phenomenon is being called "ice mode" although Lotus does not have such a mode.There is no thought that rake or tire stagger is causing the problem but they are scratching their heads as well.

pcar964

1) If the GT3 brakes go into an unpredictable "mode" where F/R bias changes dramatically when the sensors decide the ABS is malfunctioning, that is the singular MOST DANGEROUS THING I've ever heard of, WTF WAS PORSCHE THINKING?!?!?!?


2) If I'm reading the post incorrectly, and the ABS just turns off normally and the bias stays the same... and you got into trouble simply because the ABS wasn't working, you need to learn how to brake better. Far too often, ABS is used as a crutch, and I believe it does nothing but promote bad driving habits on the track. (sorry for the OT rant )

roberga

964: When that failure light comes on, the ABS shuts down, the computer ****s the bed and the bias is almost totaly on the front. I was told by Porsche that bias goes there to prevent the rear from coming around.

skea: could you have tricycled with the brakes applied? If so that will do the trick.

pcar964

That's unbelievable! Am I missing something, or is Porsche basically assuming that GT3 owners are too stupid to drive a non-ABS car without spinning it immediately??

God I hate electronics in cars...

PS - if your cars are anything like my 993, the brakes are already biased too much towards the front...