The Right Wheel for your C4 - Fitment Fix

'84-'87 Corvette Wheels Dilemma Solved

Cam Benty Apr 1, 2004 0 Comment(s)
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The huge 11-inch-wide wheels in back wrapped by Sumitomo GT tires from Tire Rack make for amazing handling and braking performance gains. Besides the improvement in tire patch, the larger wheels give greater clearance for larger brakes.

A significant fear for anyone buying wheels for their C4 ('84-'96) is purchasing the wrong ones for their car. It's embarrassing to purchase an expensive set of wheels and tires, only to find they stick out of the wheelwells (or tuck in too far) or, worse yet, rub the fender lips when you turn the steering wheel. Either way, with the price of custom tires and wheels these days, having an interference problem is bad news.

The biggest issues seem to occur with the '84-'87 models. According to Mike Sweeney of Corvette Wheel Specialist, these wheels were special, with a 36-38mm offset, different from the more common 56mm offset found on '88 through '96 Corvette wheels. "Offset" is the distance between the front of the wheel and where the wheel mounts to the disc-brake rotor; backspacing is measured from this point to the back of the wheel.

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"This is a common problem for new Corvette owners who are interested in going to an upgraded wheel for their early C4 Corvette" says Sweeney. "They find that, while there are a great number of good-looking wheels for the '88 and newer Corvettes, including ZR1 wheels, there is definite confusion as to what fits."

When originally built, the '84-'87 Corvette was delivered with P255/50-16 tires on 16x8.5 or 9.5 wheels, depending on exactly when the car was built. According to Sweeney, most owners of these cars don't know which width wheels they have until they change tires because the factory was never consistent with delivery. The factory bolted up the wheels it had in stock, rather than sticking with one size throughout the run. The factory changed wheel sizes often due to vendor changes. However, tire sizing remained unchanged at P255. Regardless, the backspacing on the wheels was between 36 and 38mm, and bolt circle was consistent at 5 on 4.75-inch.

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"Owners of these cars looking to run the '88 and newer wheels will have to use an adapter to make up the difference," says Sweeney. "I have not seen a problem with running these larger adapters on the street. It's the easiest way to run the larger 9.5- to 11-inch wheels used in the 17- and 18-inch tall-rim widths (no 11-inch-wide rim is offered in the 18-inch-tall wheel from the factory). This is a popular swap for those looking to run the biggest tires possible. For standard, street-driven '84-'87 Corvettes, you can use a 17 (or 18) x 9-inch wheel (with adapters) with P275/40-17 tires all around, which allows you to rotate them for optimum tire wear. For the ultimate hot-rod upgrade, you can stagger the tire/wheel combination P275 tires up front and massive 17x11-inch wheels (without adapters) with huge P315/35-17 tires in the rear."

The beauty of the larger ZR-1 wheel is it was built with a 38mm backspacing. This means '88 and newer Corvettes cannot use the ZR-1 wheel because they will stick out of the wheelwells. In addition to the ZR-1 wheels, there are other exceptions to the 56mm rule with '88-'96 wheels.

"There are two exceptions to the standard 56mm offset ruling for '88 and later Corvette wheels," says Sweeney. "The '96 Grand Sport Corvette coupes came with 9.5-inch-wide wheels and a 50mm backspacing. These wheels came only in black, and on the convertible used a smaller 8.5-inch wheel width due to the encroachment of the convertible-top well, which necessitated a smaller wheel width. The other exception is the '96 Collector Edition Corvette that also featured similar 56mm backspacing with 8.5-inch front and 9.5-inch rear wheel width."

Overall, there are many wheel combinations available for your Corvette. While there are more challenges to early C4 ('84-'87) Corvettes, with wheel adapters and a few careful checks, you can have larger tires on your car than you might have imagined. Regardless of what you do, check for fitment before leaving the shop. Interference problems are more than just a nuisance; they are unsafe and should be cured before they occur.

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The offset difference between the '84-'87 36-38mm rear wheels to the 56mm offset with the '88-'96 wheels is frustrating for owners looking to run larger wheels on their early cars.

Quick Tips
* Use new lugs and valve stems when installing new tires and wheels. Use only conical lug nuts on factory wheels.

* Torque your lug nuts to 98 lb-ft.

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With ZR-1 17x11-inch wheels, the offset is 38 mm, perfect for '84-'87 Corvettes, but a problem for '88 and later cars.

* Use stick-on weights instead of the outside hammer-on weights from the factory. The stick-on wheel weights create a better-looking final appearance and better balance for the wheel and tire combination.

* Remove any tire-inflation sensor systems from your wheels. There are no replacement parts for these systems, and they will probably break in the future. Remove these internal sensors and put them in storage. Remove the instrumental panel inflation sensor bulb from the dashboard. According to Mike Sweeney, never attempt to retrofit the OE tire-inflation-sensor system on any C4, early or late.

Sources

The Tire Rack
South Bend, IN
888-541-1777
www.tirerack.com
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