A Quick and Accurate Way to Determine Proper Wheel Sizing

Words/Photos: Cam Benty

Determining the perfectly sized wheels and tires for any vehicle can be a challenge. But, for car builders, where custom bodywork and suspension changes can come into play, it’s a downright black art. After all, we all want the largest wheels and tires possible for the biggest footprint — but can’t stand when they rub the fenderwells and other suspension parts.

For our 1971 Pontiac Firebird, the issue became that much more challenging due to the installation of the Heidts front subframe and Independent Rear Suspension (IRS). The IRS places the brake calipers inboard, far away from any wheel conflicts — or so we thought. For certain, we needed some way to properly measure the opening to determine proper wheel width and offset along with tracking tire interference.

So, Scott Blair offered up his innovative WheelFit product that takes the guesswork out of wheel sizing. The WheelFit works with 4-, 5-, 6-, and 8-lug wheels and expands to handle 14- to 28-inch wide tire beads and wheels measuring 6.5 to 16-inches in diameter. For anyone not versed in wheel /tire dimensions, that should cover just about any street application used today.

A key ingredient to our test is the fact it requires a tire to hold the WheelFit device in place. The WheelFit measuring device is inserted into the tire and then bolted to the hub. The tire can then be moved inward or pulled out to the outer section of the wheelwell. For front tires, you can rotate the tire through its various steering angle to check for conflicts.

The Install

We watched the YouTube video (a DVD is also supplied) to understand fully how the WheelFit is installed. The first time we installed the device, it took two people to hold the various sections in place. After a couple of times, our competency increased and the tool became much easier to install.

Our first test was to install a Pirelli P255/40-20 tire in the rear section of the Firebird. Our version of the WheelFit maxes out at 20 inches, perfect for this install. The same device can be used for as small as 14-inch wheels without issue. The bolt circle system is genius for its adaptability to a wide range of bolt circles.

It should be noted the WheelFit will not support your vehicle, so when measuring the tire/wheel sizing, both the vehicle and the suspension must be supported. For this reason we needed two floor jacks, along with a jack stand to support the car, just in case. Note that when jacking up the suspension to give the proper suspension angles, not to lift the vehicle off the ground. The perfect set up is to have the tire touching the ground with slight friction to simulate on-road placement.

Sources: WheelFit, thewheelfit.com; YearOne, yearone.com