Pontiac GTO Wheel and Drag Bag Installation - Hookin' Up A Goat On A Budget

The factory WS6 wheel that was available on '98-'02 LS1-equipped Birds measures 17x9 inches, or a full 1 inch wider than the stock GTO wheel. It is a 5-lug, 4.75-inch pattern with a 50mm offset and 6.95-inch backspacing. They are available on eBay and through restoration sources for reasonable costs. This O.E. reproduction was purchased from Lakeshore Wheel and Tire and retails for $212.50 each (Part No. 65311D-R) in a polished finish. A silver/machine polished wheel is also available under Part No. 65211D-R for $187.50 each. Since the stock tire size on a WS6-equipped Firebird is 275/40ZR17, the MT ET Street Radial fits perfectly.

Bob Cook purchased a pair of used WS6 17x9-inch rims on eBay for $200 total, including shipping. (In order to match the silver finish on the stock GTO rims, the WS6 rims were sent over to a local powder coater where they were sandblasted and then powder coated in silver for $130.) Although the bolt circle on the WS6 rims is very close to the GTO bolt circle, for safety sake, the wheels were sent over to Pro-Tech Machining in McKinney, Texas, where senior CNC machinist Eddy Noble set the wheel up on a CNC mill.

The first order of business is to make sure that the wheel is square on the machine. Two pins are used to positively locate the wheel on the machine and a dial indicator is set up so that the exact center of the wheel can be located. After determining the exact center, the two pins are snugged tight and the wheel is checked again to make sure that the center is aligned.

Since the bolt circle is off by 0.0256-inch (4.750 vs. 4.7244), the countersunk area of the lug nut holes has to be moved toward the center of the wheel by 0.0125-inch to provide the correct bolt circle for the GTO pattern. In addition, to retain the original GTO lug nuts that feature 60-degree chamfers, the 45-degree chamfers on the WS6 wheels will be machined to 60 degrees.

A multi-fluted countersink is used to perform the machining operation. (It is physically possible to bolt the WS6 wheels onto the GTO without modifications; we have seen racers do it, because the holes are large enough to accept the difference in bolt pattern. However, when the GTO lug nuts are installed, not only is the GTO chamfer incorrect for the WS6 wheel, but the placement of the countersunk area in the wheels causes the GTO lug nuts to side load the studs when the nuts are torqued. That is why we recommend this machining, which will result in nearly 100 percent contact between the lug nut chamfer and the countersunk holes and no stud side loading.)

Once the machining is complete, the rim now wears a metric GTO bolt pattern and the proper chamfers for the lug nuts. The total cost of machining was $75.00 for the pair. In summary, a total of 1 inch of additional rim width was achieved. Whereas the GTO rim carried a 48mm offset on the 8-inch rim, the WS6 was marginally different at 50mm. Without getting into fancy offset calculations, suffice it to say that the wider wheel effectively allowed the tire to stay in relatively the same center in the wheelwell, yet add 11/42-inch of width on the inboard and outboard sides of the wheel.

The M/T tires were then mounted and balanced at a local Discount Tire store, where the technician used stick-on weights. As expected, the larger tire would not clear the inner fender lip even on a half-throttle brake torque launch. Note the blue chalk on the tire and the cut line on the sidewall-hence the need for the airbags.

Since the decision had already been made to preserve the inner fender lips, in order to gain the necessary clearance to run the wide tires, a set of GTO rear airbags (Part No. DB001, retail $99.95 a pair) was sourced from BMR Fabrication. Included in the kit are bags, plastic tubing, hose clamps and all the accessories necessary for installation. The GTO drag bags are an inexpensive, yet very effective, means to modulate the independent rear suspension's spring rate. When inflated, the air bags will stiffen the rate of the rear springs, effectively limiting vertical wheel travel.

With a projected installation time of 2-3 hours, the GTO was delivered to Real Performance Motorsports in Lewisville, Texas, where the late-model performance specialists could quickly and efficiently get the job done. Once on the lift and after removing the 22mm lug nut covers and the 19mm lug nuts, the wheels are dismounted by RPM technician Matt Garzonie. (The faces of the stock wheels have been covered by a multi-prismatic vinyl tape. Depending on the angle of the light that reaches the tape, the faces will either look orange or a deep charcoal color.)