This I was anxiously awaiting--trying out R-compound tires on Project M3. Toyo sent out a set of its new RA1 tires (sized 235/40-17), quite a favorite track tire among BMW CCA club members, as I came to realize later in my testing day. Each tire weighed in at exactly 23.25 lb and came with 8/32-in. tread. The thick, aggressive side blocks on the tread appeared to mean there would be serious cornering g-forces generated. Although D.O.T legal, Toyo didn't design the RA1 for street use, but one could easily use these to commute to and from the racetrack, saving the time from changing wheels there. This gave me an extra 45 minutes of sleeping time the morning of the test, and I also didn't have my car weighted down with an extra set of rubber-stinking wheels on the way up.
I took the car to a Driving Concepts event held at Willow Springs Int'l Raceway. To test the differences in tire performance from the P7000s to the RA1s, I took my indicated cornering speeds in turn 2 and compared them. Turn 2 is a long, sweeping 180-degree turn taken in fourth gear, at least in the case of this M3. (Exiting this turn incorrectly is what claimed my previous M3, so I was sure to give myself an extra foot or two of space while exiting the turn this time.)
At 105*F it was hotter than the last time (92*F), but the M3 performed well and had no cooling issues, even with the newfound power (the evosport pulleys were not installed at this time). The Ground Control racing suspension wasn't messed with too much--I kept the same camber, shock stiffness and swaybar setup as last time, but the car had been lowered about 1.5 in. with a 15-minute ride-height adjustment. (I still have a lot of fine-tuning to get the suspension setup to feel just right.)
The Toyos performed very well up through Turn 2--the speed in the middle of the turn went up by about 6 mph, a remarkable improvement. But toward the latter parts of each session those speeds began to drop with the RA1s. The left rear, in particular, began to lose grip. A couple more laps and the car began to power oversteer up turn 2, enough to make me ease off the throttle a bit. It didn't occur to me until later that powering up turn 2 in fourth gear at around 5000 rpm was causing the tires to want to brake loose because of the new power with the cams and exhaust--I was right in the peak torque range!
The new upgrades continued to instill a little fear in me. Exiting turn 6, a righthander that has a small elevation change both up and down as you're still turning, used to be quite easy--just power out of turn 5's left-hander and continue holding the gas pedal down as you go through turn 6. With the new setup, however, I had to make sure I had the perfect line while going over turn 6's "hump." With the added grip from the Toyos out of turn 5, as well as the extra torque, the car would reach the crest right at about 5000 rpm in third gear, just as the car gets light. Again the car was right in its powerband, making it difficult not to lose rear-wheel traction and provoke oversteer. Unless I got the perfect line out of turn 5, I was forced to either short-shift to fourth or slightly lift up off the throttle while going over the hump, holding it in third gear--I chose to stay in the powerband and held it in third.
Entering turn 8 was also now a new experience. The last time I was here I could hold the pedal down from turn 5 through turn 8, reaching a speed of around 125 mph with the all-season Pirellis before braking for turn 9. This time, however, before ever beginning to turn for turn 8, I was already passing an indicated 120 mph. The extra several hundred rpm I got exiting turn 5 from the Toyos got me a few more mph of a head start, only to have the extra 20 or so hp add to the effect. In an attempt to be a little safer, I came off the throttle about 40 percent for a period of about 1-2 sec. through turn 8, and then full-throttled again until having to brake for turn 9. In the end, I still realized laps that were over three seconds faster than with the street tires. And at a high-speed track like Willow Springs, three seconds can be over a 500-ft difference down the start-finish in an M3--that's a lot of car lengths! One main advantage to running R-compound tires is they can withstand a lot of heat before breaking loose. Just make sure you do a warm-up lap first--do not do a hot lap right out of the pits.
Thanks to Louie Lugo of Big 0 Tires in Redlands for mounting the Toyo tires and to Carl McGinn and Judy A. Ray of Driving Concepts for allowing me to conduct these tests at their driving event. Driving Concepts is well organized, utilizing various tracks around the country and at the Nuerburgring in Germany.
Big O Tires
525 W. Redlands Blvd.
Redlands, CA 92373
67 Tennis Villas
Dana Point, CA 92629
Fax: (949) 489-9432
Toyo Tire Corporation (U.S.A.)