What defines an aggressive street car? Paint, a thumper drivetrain, and stance are all important, but it usually comes down to monster tires. For the last 15 years, Pro Street has led the way with a killer look revolving around steamroller rear tires. But that image is changing. If you are one of those Chevy faithful who really likes pushing the envelope, the best way to do that is by subscribing to the Pro Touring concept with fat tires at all four corners.

If there is a lost art amid street machiners, it has to be fitting fat tires. How many times have you seen an otherwise good-looking street car all jacked up to clear big tires? Or, even more common, the sliced and diced sidewalls that come from the tire rubbing on razor-sharp wheelwell openings? Most enthusiasts do little more than take a barely educated guess at rim and tire size and then hope for the best. But, if you are going to spend up to $2,500 on tires and wheels, you should spend a couple of hours making sure the rolling stock fits properly. This story will help you do just that.

Measuring Up

While tire height, width, and rim size are important measurements for fitting fat tires, there are a couple of other measurements that are also critical. Few enthusiasts take into consideration wheel backspacing and the overall tire width when mounted on the wheel when measuring for tire clearance. The next important dimensions are accurate maps of both the front and rear wheelwells to ensure that your tire and wheel will fit properly without interference.

The first step is to build a very simple wheelwell clearance device out of 1-½x1/8-inch angle iron and a length of ¼-inch threaded rod. As you can see from the photos, the angle iron bolts to the brake hub and then uses a threaded rod to accurately trace inboard and outboard sidewall clearance. When taking these measurements, always check that the rear axle is at ride height and not extended to full droop. Use a floor jack to place the axle at ride height. You could also remove the springs to check clearance with the car at various ride heights, but it’s not necessary.

It’s also critical to check clearance on all four wheelwells to ensure that the car sits on the frame squarely. On our test car, we found the body to be shifted to the left relative to the frame, creating a tighter fit on the right outboard and left inboard areas. To remedy this situation, loosen all the main body mount bolts and shove the body in the appropriate direction to center it over the frame.

When checking the front tires for clearance, always move the steering to full-lock in both directions to check for interference. This is where the checking tool really comes in handy. This tool will immediately show you where the tire will hit with the steering at full-lock. On our test car, we found that with maximum backspacing the tire would hit the sway bar in one direction and the upper control arm in the other full-lock position. Since this interference occurs at almost full-lock, and generally at very slow speeds, this may be acceptable. If you are aware of this, you can usually avoid scraping the sidewalls. An additional steering lock stop extension would also prevent the tire from rubbing.

Once the measurements are complete, it’s a judgment call as to how much tire clearance is acceptable. We suggest ½ inch on either side of the tire as a clearance, but we’ve seen successful fat tire stuffs with as little as a 3/8-inch clearance. For rear axle applications, one additional step is to limit lateral (side-to-side) movement of the rear suspension as much as possible. For coil spring cars like Chevelles, Impalas, and third- and fourth-generation Camaros, the best idea is tubular lower control arms by Global West, Hotchkis, and Art Morrison. Our personal experience is these components do an excellent job of reducing lateral movement inherent with stock-type, stamped factory control arms. This is crucial with sidewall tire clearances of less than ½ inch.

For rear leaf spring–equipped cars like first- and second-generation Camaros, the best plan is to use reduced-deflection bushings such as polyurethane, or a set of Global West’s Del-A-Lum bushings to limit lateral deflection. In this situation, the Global West bushings do a better job since they offer little lateral deflection. This is especially useful when negotiating steep driveways when one tire angles up into the wheelwell. Taller tires are especially vulnerable to lateral movement and scraping in these situations. We know of an early Camaro that had 1 inch of sidewall clearance and still rubbed a set of 275/60R15 tires on a not-so-steep driveway. Shorter sidewall tires are less susceptible to this problem.

Once all your measurements are complete, one of the biggest problems is finding a set of wheels that match your requirements. It’s often difficult to find a wheel style you like that will also fit within the narrow confines of what you need. American Racing, Budnik, Weld, and others will build custom offset wheels (within the limitations of the wheel) that can be specified down to as little as 1/8-inch backspacing increments to fit your needs. The best thing to do here is to call the specific manufacturer and see what services they offer. Of course, you can expect to pay a little more for custom-offset wheels than standard off-the-shelf ones.

As far as tires are concerned, keep in mind that the tread is not the widest portion of the tire. Depending upon the width of the wheel compared to the tire, the sidewall width (referred to as the section width) can add ¼ inch or more per side to the width of the tire.

Another factor that is less well known is that tread and section widths vary greatly between manufacturers with the same size tire. For example, we measured a 245/50ZR16 Goodyear, Firestone, and BFGoodrich tire and found that, even when mounted on the same size wheels, the section widths varied by as much as 3/8-inch. Tire heights were all very close, but the section widths varied substantially. This becomes critical when changing tire brands. As you can see, there’s more than meets the eye when it comes to stuffing monster meats under your hot street Chevy. However, if you take the time to carefully measure all the clearances and select the best-fitting tire and wheel combination, it is possible to have that killer, fat-tire look in even a daily driven street car.

American Racing
1275 Davis Rd., Suite 300
IL  60123
Fat Man Fabrications
8621-C Fairview Rd., Hwy. 218,
Dept. SRM Web
NC  28227
1 Parkway S.
P.O. Box 19001
SC  29602-9001
Global West Suspension Components Inc.
1455 N. Linden Ave.
Budnik Wheels Inc.
Huntington Beach
CA  92647
Hotchkis Performance
12035 Burke St., Ste. 13
Santa Fe Springs
CA  90670