That was my understanding of TC originally, but from talking to a lot of different people (and reading the Porsche web site ), turning off TC on the GT3 also turns off/raises the limits of ABD and ASR. I felt ABD was very intrusive on the track, and also was responsible for beating the crap out of my rear pads and rotors. I don't know enough about how the ABD and ASR sensors and systems work to know if there is any comparison going on between front and rear wheel speeds. If so, that's where a difference from "expected" wheel diameter might have an effect. But there may not be those comparisons going on. Certainly with TCS (and therefore ABD and ASR) turned off, I never had an issue. I only mentioned it because, if anyone does feel the car acting a bit off with the smaller diameter tires on, it might be worth trying an experiment and shutting TCS off to see if the problem goes away.

Interestingly, once I started running with TCS off, my rear brake wear (pads and rotors) got MUCH better. With TCS (and therefore ABD) on, the car happily starts braking one wheel or the other if it thinks it's starting to yaw too much, which wears everything a lot faster.

Finally, in my opinion running with TCS off does make a difference on lap times because it isn't simply traction control, it's stability control as well. I probably improved by a second or two per lap, it's hard to say. I was able to get the car to rotate much more easily because I wasn't fighting the TCS/ABD system the entire time. Also, I've ridden with a bunch of pros in my car, and every one of them turns TCS off immediately after they start the motor. So that says something.

 

+1

If you look at the relative sizes of the 245/35 vs. 245/40 Hoosiers, you will see that the 245/35 tire is the appropriate one from a front to rear ratio standpoint.

Hoosiers 245/35 = 24.7" tall; 315/30 = 25.6" tall
By contrast the 245/40 is 25.7" tall, actually taller than the 315/30 rears

OEM Michelin Pilot Sport Cup 235/35ZR19 = 25.5" tall; 305/30 = 26.3" tall
About the same front to rear ratio as the 245/35 / 315/30 Hoosiers

If there is any ABS problem, it would more likely be with the taller 245/40 Hoosiers. I am not sure why you would want to run a Hoosier on the front that is taller than the rear, and also rubs.

 

The comparison to the OEM 19s is highly instructive and sound correct, now that I think about it. If both front and rear diameters shrink by about 1", the ratio stays pretty close to stock which should make the car's electronics, including the ABS, happy. On the issue of TC on or off, I don't doubt that we can feel the difference and that maybe it is increasing rear pad wear. But I would still like to know, objectively, which is faster.

 

As I said, my times were typically 1 - 2 seconds faster per lap on my local track with TCS off vs. on. But I hope some of that was me getting better as a driver, too .

Perhaps doesn't qualify as "objective", but one of the people I worked with this year was Joerg Bergmeister. In addition to driving with the Lizards in ALMS, he also does a lot of development work with the factory on the street cars (including GT3 and GT3RS). He stated that without a doubt TCS off and Sport suspension on (on all but the very roughest tracks) yields the fastest times in the GT3. So I don't doubt that's the fastest setup for the car. The other factor, though, is the driver, and in that case everyone is different. I can easily see some drivers being faster with TCS on rather than off because of their particular driving style or skill level. So I think everyone needs to experiment and figure it out for themselves.

 

I would happily accept Bergmeister's opinion. But I would still like to see it tested. I know that, for example, I am 2-3 seconds per lap faster on R6s than R888s on a (plus or minus) 1:30 track because I ran them back to back. I wonder if the TC on or off would yield the same differential. Next year...

 

terry- no offense but the only way you're going to get 2 seconds of help per lap from TCS is if you're sliding the crap out of the car on every exit and going off track from excessive wheelspin...

TCS slows the car down! it is not an E-differential, nor is it needed due to crazy torque/weight ratio like an F1 car. the gt3 stock has tons of mechanical grip and going for that last bit of time in the car on most tracks is more related for going really fast on entry- how often does the car in 3rd gear turns get totally out of sorts under acceleration?

 

Terry - Absolutely, the only way to know what'll work for you is to try TCS on/off back to back.

CJ - I agree, extracting the last tenth or two in a corner in a GT3 is all about carrying more speed in and using that to help get a little bit of extra rotation out of the back end. Not only do you slow a little less, you can get back on the gas a little sooner because it takes less time to get the car pointed where you want it. The TCS system (specifically ASR and ABD) interfere with that. But if someone would otherwise be overdriving the car, the TCS system will help them and probably save some offs.

 

All of which is why I asked the question in the first place, is the car faster or slower with TC on? cobrien thought faster by 1-2 seconds/lap and I said we need to test this.

 

My guess is it is track dependant.

At Watkins, where you were flying i can't imagine you would be slower with tc on - but maybe on a track where more rotation into a corner is required (limerock) it would be faster.

Now, if you were a faster driver than 2:14 at Watkins with a totally stock 997gt3 on stock oe tires then TC i would have to think could only be a negative


CJ, I have been on the track with terry, he is a fast smooth driver.

Terry, I like the question as I have thought about it myself, i.e. TC seems to have a very very high tolerance and I also thought in some situations it "may" allow you to be a max grip threshold on exit - thus being faster - but as i am getting faster in the car, my hands are now making micro corrections to stay on the slip angle way before tc would ever hit so i'm left with the fact that it can only likely be a negative for fast drivers when they are using entry speed to rotate the car and any tc would only kill power

paul

 

Hey, Paul - thanks for the compliment. Haven't seen you for a while. I suspect that your surmise is correct, but I also wonder how the TC interacts with the LSD, plus the electronic goodies. Anyway, it's up to the warm weather drivers now. I assume you are still in the frozen North. Snow tires on the GT3 again this year? Mine go on tomorrow.

 

- i think you may be onto something about the lsd and the tc
- with my upgraded guard lsd, with tc (on) coming onto the front straight (turn #10) at mosport the lsd is really working and if tc is on (it does not flash) but it "feels" a little different
- it is possibly that it is taping the brakes / killing the throttle without the light flashing but it difficult to be sure

- we got snow here yesterday and i missed my window to get the snows on
- should warm up again and give me another chance
- there is a small track with no walls about an hour away and i may actually try and do a slight snow day with the car this year
- rain days at mosport are just so hard on the nerves because one mistake and the bill starts at 40Gs

 

This thread is getting deep...

I got my spare wheels (they look sweet, pics later) and I am getting MPSCs because the Hoosiers won't get here till after all my track days, at which point Black Betty will have to have to go in for her nose job (hood and fender repaint and paintshield)...

New question: I have to drive around 340 km (~212 miles) to get there averaging speeds of 200kph (~125 mph) and have no choice but to drive up with the track wheels and MPSCs on the car.

Is there anything special I have to be careful with in terms of tread maintenance for the drive up and before I go on-track?

I'll obviously have standard pressures in the tires for the highway drive, lower for the track, slow down for any rain, etc. My main concern is that my on-track "sticktion" will be affected because the tires will just have been through lots of highway wear.

 

- no issue with driving the tires to the track
- i drove to VIR and back (1500miles) on mpscs
- just slow down if it rains
- if you are running lots of camber, pump up the tires to a high level to save the inside edges (i.e. by inflating the center of the tire more)

 

Cool, thanks much!

 

Just drove 1100mi back and forth to VIR on the OEM MPSC with no issues. They work very well as street tires, just be careful in deep water and very cold weather.

As for TC on/off, I always drive the GT2 with it off (and PSM off too). Although the intromission of TC is very smooth, IMO it always better to get the full feedback as a driver of what the rear end is doing, otherwise you are missing handling the car at 10/10ths which is when the slidey stuff begins to happen. Also in our cars with such rear weight bias and big tires, most times some wheelspin in higher gears (2-3-4) out corners doesn't slow you down, as thanks to the LSD you still get a lot of forward momentum and the "sliding" helps to finish turning the car around the corner (increased yaw rate).

I can understand, why you might want it ON for safety while you work on improving the line, braking, etc, but there's a point in the learning curve where you have to take it off.