ldw

Myself and Keith Alexander took identicle GT3 street cars without modification except for safety items to the PCA event this past weekend at WG. My car weighs 3160-no driver, no fuel. The ride height and all components remained stock, including wheels and brake pads. The front camber was increased to 1.9 and the rear 2.0, with a caster of 8.4 degrees.

We tested 3 different tire varieties. The Dunlop SP race(245/285) was actually driven to the track (4 hour drive) and then back to NYC by KA. This tire was very progressive, felt comfortable on the street and had excellent tread remaining. Because of the significant tread depth, this tire had a significant disadvantage over the MPSC(235/295)and Dunlop slicks(235/280-650). The Dunlop was easy to drive, gave excellent warning at the limit, and had the most compliant side wall providing for a smooth ride over bumps and turtle curbing.

The MPSC provided quicker lap times, had a stiffer, less complaint side wall, with subsequently more rapid response to steering input. They do not come up to temperature as rapidly as the Dunlop, but when up to temp, perform extremely well. Wear was excellent.

The Dunlop slicks of course provided the best grip, but as expected, gave the least warning at the limit. Wear was excellent.

Top speeds with the 3 tires were:
Dunlop SP 153 mph, MPSC 154 mph, Dunlop slick 156 mph according to the digital speedometer at brake marker 6 at the inner loop.
Difference in lap times was 7.0 seconds between the 2 Dunlop tires, with the MPSC falling in between.

The Dunlop is an excellent all around street/track performance tire that may be very good in the wet but we did not test that. The MPSC is quicker and more responsive, but will not be as drivable on the street and wet weather driving is a challenge. Slicks are the quickest, but not allowed on street, are most expensive and have an extremely short life. It seems that all 3 succesfully performed for the job the were designed for.

ringmeister

I'm feeling pretty good, I had 155 indicated bone stock.

Good info, I think I'm going to try the Pirelli Corsas. Anyone have any opinions on those?

ringmeister

Ooops, never mind. I found the comparison info in another thread.

ldw

The stock speedometers are often out of calibration and are set up for the Michelin street stock tire as delivered. This is confirmed by the fact that KA and I often did not get into 5th gear which according to the gear charts should be happening at approx 141 mph with a tire of 25.0 inch diameter. The mph are provided for a comparison among the 3 tires in the same car, same driver. The Dunlop SP has a diameter of 25.0 inch, MPSC 25.2 inch, and Dunlop slick at 25.4 inch. Hence, the actual top speed for the slick is relatively higher (than that documented)compared to the other tires given it has the largest diameter.

Larry Herman

So what kind of times were you running?

ldw

Both drivers=2:10 in race traffic. Both Keith and I were within tenths of a second of each other (with respect to fastest lap) in both the sprint race and the enduro. This is approximately 10 seconds slower than times we would do in 2004 GT3 cup cars.

Larry Herman

Thanks Lynn. I assume that is with the street Dunlops. What were you doing going into the esses? Did you just lift, or did you have to brake?

ldw

NO, with slicks. The Dunlops are 2:16-2:17s. For additional perspective, none of the cup cars ever broke 2:00 and this even includes Jack Baldwin in a Cup car in Grand Am SGS trim testing for the 6 hr race this weekend. There is a significant lift in turn 2 and a slight lift at top of hill going into esses even on slicks. In a cup car, when the set up is right, we do not lift from the time we leave the apex of turn 1 until the bus stop brake zone. The times are reliable with respect to the car as KA and I would independently turn the same times within tenths of a second in any given session-with same tires, despite not being able to see each other on the track most laps.

Those who feel this car is "close" to a cup car in lap times, have obviously never driven both cars back to back. The GT3 street car is an incredible vehicle, but the Cup car is capable of significantly quicker lap times at a long momentum circuit such as Watkins Glen.

Larry Herman

Thanks again, Lynn. It looks like I will have a significant learning curve when I get there in July. In my old Carrera it was no lift either, but I couldn't get down to the esses fast enough, and I could pretty much drive any reasonable line through there. Did manage to turn 2:18s, but that was with club racing setup.

ldw

Larry,
Do not be disappointed if your times are not as quick as you might expect. Even if I could completely change over the entire suspension, transmission, and other goods to cup car specification,.......the car is relatively heavy and that is the challenge in braking, through the corner and out of the corner.
It was really fun though!

Johninrsf

Lynn,
What tire pressures were you running with the MPSCs?
Thanks,
John

ldw

Pressures we ran for MPSC were 32 F, 35-36 R hot.

macfly

I too had read here that there wasn't such a difference between the two, but I was at my local track, Willow Springs last week, and for the first time was there with an open exhaust stripped out Cup car. I did my best ever time of 1:38.1 and I thought I was flying. The Cup car was a full 12 seconds faster, and the guys running it were feeling there was something wrong with it because it should be going much quicker! I know I'm not the fatsest driver out there, but I was amazed how much faster the Cup car was.

ldw

If it is the car in the picture, it appears to be in Grand Am Cup trim with series SGS class Hoosiers. These are very good tires but they are not quite as quick as say Dunlop or Michelin race slicks. Hence, if on slick tires such as the Dunlop for example, it would have been even faster.

Johninrsf

Andrew,
When I was last at WSIR, 5/29-30, (with TCCRA), the fastest P cars were consistently doing 1:21s!!! Times were recorded from transponders.
Incidentally, you and I are within .25 of each other. I think we have another 8 seconds, or so, left in this car (or more). I think MDS may already be there!
JP