When released to the public, the newest generation of GTO quickly became known in automotive circles as one of the most refined platforms to hit the U.S. marketplace. A true performance coupe by any definition, the Goat offers impressive handling, ride characteristics and stellar performance.
Achieving maximum acceleration and obtaining the ability to push the car harder through the turns, however, is hampered by the OEM design of the front and rear wheelwells that leave little room for larger wheel/tire combinations. From the factory, the standard 5-spoke aluminum GTO wheel (PZ9) measures 17x8 (43.2 cm) and is shod with BFGoodrich P245/45ZR17 G-Force TA KDW tires (there was an 18-inch wheel option, as well). Mounted on the stock rim, the section width of the tire is 9.6 inches with a diameter of 25.7 inches. Clearly, a larger rear tire would help in the quest for better acceleration, but how can this be accomplished without having to perform surgery on the rear wheelwells of the GTO?
Seemingly from day one, hobbyists have been trying to stuff the largest tire possible under the GTO, creating a dizzying array of choices. By far, the most popular one out there is to purchase a drag radial in a P275/40-17 size, mount it on the stock rim and then roll the rear inner fender lip to provide enough clearance so that the lip doesn't come in contact with the tire when the car is either launched at a dragstrip or driven aggressively on the street.
Although most tire manufacturers say that the acceptable practice is for rim width to be plus or minus 1 inch from their optimal recommend-ation (which is 9 inches for M/Ts radials), mounting a P275 tire on an 8-inch rim forces the sidewall to "pooch" out, effectively shortening the overall mounted diameter of the tire, so we prefer to go with the 9-inch rim.
If that's not enough, although the rear inner fender lip may be rolled with a specialty tool, you risk damaging the body in the process, and you are lowering the potential collector value of your GTO.
Is there another way to get wider rims and fatter, stickier tires on your GTO without performing surgery on the body or breaking the bank? Follow along as we modify ($75) and install a set of used 17x9-inch WS6 wheels, ($200 for a pair) shod with Mickey Thompson's 275/40R17 ET Street Radials ($189 each). A set of BMR's GTO drag bags ($99.95) will be employed as well to keep the wide tires away from the inner wheelwell lips on the '06 GTO owned by Bob Cook from Allen, Texas. Other than a custom dyno tune (HPP, July '07), the automatic equipped car is stock. Now let's get to it.
Conclusion
Following installation, air was pumped into the bags and the system was tested for leaks. BMR reps recommend running 8-10 pounds of air minimum and adjusting accordingly to provide just enough pressure to keep the tires from coming in contact with the rear fenders. After a few adjustments, 10 pounds was dialed in and the GTO was taken out for street testing.
Bob told HPP, "The ride characteristics of the GTO with the drag bags set at 10 psi are all but indistinguishable from the ride before installing the bags. What the bags do provide is the ability to run larger tires without resorting to rolling your inner fender well.
"The stock tires would spin on launch and then on the 1-2 shift very easily, especially after the custom dyno tune from Real Performance Motorsports. As soon as the Mickey Thompson Tires were installed, it was a totally different story. The tires just flat-hooked and went, without any spinning either at launch or on the 1-2 shift. I am looking forward to getting the tires tested at the track and finding the optimal launch point with the drag radials.
A comprehensive strip test of the M/T ET Street Radials vs. the stock tires is forthcoming. As an added bonus, the same M/T tires will be tested on a solid-axle Fourth-Gen Firebird. Stay tuned as both sets of stock tires and drag radials will be obliterated as necessary.
Supplies Required:
Pry bar
Cutting tool
(Hacksaw, Sawzall, cut-off wheel)
Metric socket set
Metric wrenches
Torque wrench
Drill and Drill Bits
Pole Jack
