As launch rpm was increased, the 60-foot times came down. After determining that the 60-foot times steadily improved through 4,000 rpm launches, the tire pressure was reduced to 12 pounds to see if traction could be further improved. Simultaneously, the launch rpm was increased to 4,500. Not only did the M/T tires like the lower tire pressures, but the more power that was put to them, the better they hooked. With a 2.06 60-foot time logged from a 4,500 rpm launch, the Formula was driven straight back to the staging lanes, where the rpm was raised to 4,750 and the clutch was dumped yet again. With a second consecutive 2.06 60-foot time as a result, and the test session winding down, the 60-foot times were on a steady march downward.
Since any further elevation of the launch rpm would have resulted in an almost instant-aneous shift to Second gear, there was no reason to increase the launch rpm. Given the power of the car and the taut WS6 suspension, the results were impressive, especially since the Bird would no longer get "loose" on each gear shift. Since the Formula is turbocharged, by launching at a higher rpm, the car was able to get into the boost quicker and produce more power. The tires absorbed the extra power leading to reduced 60-foot times and the quickest (8.32) 1/8-mile time of the day. See the chart for the full breakdown.
2006 GTO Tire Test
The 2006 automatic-equipped GTO weighed in at 3,725 pounds with a half-tank of gas. The car is stock, other than a custom dyno tune by Real Performance Motorsports that bumped output up by 20.1 rwhp, while simultaneously deleting the performance robbing torque management (HPP, July '07). With 322.8 rwhp and 323.7 lb-ft of torque on tap, the 364 cubic inch LS2 GTO, equipped with an SLP Brake-Control Package, was able to raise the rpm enough on launch to find the limits of the stock tires.
After driving the M/T ET Street tires on the road with the BMR drag bags set at 10 psi, it was quickly discovered that if the car was launched hard on a sticky surface, the inner fender lip would come in contact with the tire. As a result, the air pressure was raised to 22 psi. For drag testing, the bags were set at 24 psi, since a prepped track should theoretically have more traction than the local streets
M/T's 275/40R17 ET Street...
M/T's 275/40R17 ET Street Radial (Part No. 3743R) is a DOT approved street legal drag radial optimized for dry traction. It is not recommended for use in the rain. The company recommends an 8-10-inch wide rim, tire pressures of 12-16 psi and a short burnout to activate the sticky R2 compound of the tires.
With the stock tires, the GTO was initially tested utilizing the Brake-Control Package at a starting rpm of 1,500. Right off the bat, the car pulled its best 60-foot times of the stock tire test with a 2.17 and an 8.98 1/8-mile time. On the very next run, the Goat was launched at 2,000 rpm, resulting in the stock tires spinning and a poor 60-foot time of 2.32. A second launch at 2,000 rpm produced even worse results, letting it be known that the rpm had to be below 2,000 in order for the stock tires to have any chance of maintaining traction.
To verify that the stock tires could handle the low rpm launches, the GTO was launched at 1,200 rpm on the footbrake. Instantly, the 60-foot times dropped dramatically and the run ended up being almost identical to the first run (1,500 rpm launch) with a 9.00 1/8-mile time.
Having isolated that the stock tires spun badly at 2,000 rpm, the focus turned to determining where within the 1,500 to 2,000 rpm band that spin became excessive. Since the GTO's tach-ometer is not broken down into 100 rpm increments, it was difficult to accurately gauge the precise launch point. Two launches at 1,800 rpm produced almost identical 60-foot times to the earlier 2,000 rpm launches. Any launch above 1,500 rpm produced wheel spin and poor performance.
Since the GTO was a bit heavier than the Formula, and likely heavier than the average car utilizing these tires, the initial air pressure setting for the M/T tires was 18 psi. Launching at 1,500 rpm, the first run produced the fastest 60-foot and quickest 1/8-mile e.t. With a 2.14 60-foot and an 8.91 1/8-mile, the M/T tires were already performing better than their stock counterparts.
After a second pass at 1,500 rpm to see how the GTO would perform when warmer, an 1,800 rpm launch netted a 2.24 60-foot time. Although not as quick as the 1,500 rpm launch earlier, it was over a tenth better than the best recorded 1,800 rpm launch on the stock tires (2.36). Since there was no clear indication that the M/T tires were spinning, we adjusted the air pressure to see how the tires would respond.
At 15 psi, the Goat was launched at 1,500 rpm. Unfortunately, the tires didn't respond as expected and the 60-foot times decreased to 2.30. Although spin wasn't evident, the Pontiac seemed to labor coming out of the hole, resulting in one of its poorer 1/8-mile times. With the racing session nearing completion, a decision had to be made on whether to increase the tire pressure or maintain it and perform one final 2,000 rpm launch. The tire pressure was maintained and the higher rpm launch resulted in a 60-foot time reduction to 2.26 with only a marginal improvement in the 1/8-mile e.t.
At the conclusion of the test session, it was evident that above 1,500 rpm, the M/T tires would achieve better traction and never be completely "blown-off" like the stock tires.
2006 GTO Tire Test Results...
2006 GTO Tire Test Results
Stock Tires- Bf Goodrich G-Force Kdw 245/45zr17
Aftermarket Tires- M/T Et Street Radials, 275/40r17, Utqg 0/C/C, R2 Compound
Manufactured for '04-'06 GTOs,...
Manufactured for '04-'06 GTOs, a set of BMR Fabrication rear airbags (Part No. DB001, retail $99.95 a pair) were installed by Real Performance Motorsports of Lewisville, Texas. Many high-powered Goats will squat so hard on launch that the rear suspension will bottom out on the rear bump stops, causing the suspension to unload, resulting in wheel spin or hop. Intended as a means to adjust the suspension's spring rate on the IRS equipped GTO, the drag bags allow the car to launch more effectively. Following installation, the bags were inflated to 22 pounds for street driving and after breaking in the tires, it was off to the strip to test the drag radials.