Rims ‘N’ Rubber

A guide to fitting wheels and tires

By Jim Youngs

Photos by Carolyn Youngs

Of all the decisions that we make building a replica or street rod — paint, engine, upholstery and more — we probably agonize over the selection of wheels and tires more than anything. A cool set of wheels and tires can make a critical difference between a good and bad result, as they set the overall tone and style of the car.

But, how many times have you spotted a cool-looking car, only to scratch your head trying to figure out why it doesn’t look quite right? More often than not it can be traced to the wrong-size wheels and tires that may affect the stance of the car. It can have an awesome paint job, brilliant shiny stuff and knockout upholstery, but if the shoes don’t go with the overall outfit, the whole effect is lost.

Here we are measuring backspacing, using a custom-made tool. Whatever tool you come up with has to be able to give you two measurements at the same time — the distance from the hub face that the wheel bolts to (backspace) and the distance from the centerline of the axle (radial). You can see our version in this photo — a good solid straight edge and two measuring devices. Be sure that the ruler taking the radial distance is always zeroed on the axle centerline.

A couple of additional points: Make an effort to compress the suspension as much as is safe. You want to see if there’s something in the suspension’s normal stance that gets in the way when you hit a bump. Also, use your floor jack to place the suspension in a “droop” stance. On the front you want to turn the steering to full lock-to-lock in both directions and make sure your maximum backspace dimension keeps you from hitting anything. Again, cycle the suspension through compression and droop to make sure there is adequate clearance everywhere.

Once you’ve processed all the dimensions, discuss them with the wheel company and make a decision on the specifications for your wheels. Or, if you’re considering buying wheels at a swap meet or similar, you can determine if the wheels are right by measuring the backspace using a straight edge and tape measure. Also measure the width, not including the rim beads, and its height.

If possible, it’s a good idea to mount the bare wheel (without the tire mounted) for a trial fit. Then do all the compression, droop and steering lock-to-lock tests with the car on jack stands. If the wheel hits something here, it’s not going to get any better with a tire mounted on it. You can also tape a piece of Styrofoam to the wheel and cut it to the dimensions of the tire, and try all the tests again to see if you hit anything.

Finding the correct wheels should really start at the same time you begin the project, whether you buy them at that time or not. (We know of buildups that were actually done around a set of custom wheels, so that’s not an unusual practice.)

Measuring for wheels should begin at the very early stages of construction. The first thing you want to do is establish that the outside edges of the wheel wells are equally spaced from the body’s centerline. You need to know that if you put the centerline of the body on the centerline of the chassis, that the wheel well edges are going to end up equal distances from the chassis centerline.

If not, you’ll need to adjust the body on the chassis to get the wheel well edges lined up with the chassis rails and ultimately the suspension. What you’re trying to accomplish is to end up with the suspension (wheel hubs) equidistant from the wheel well edges for both the front and rear axles. You’re not trying to make the front and rear distances the same, just match the front side to side, and the rear side to side. Keep in mind that not all bodies are perfect, with the wheel well edges equally spaced from the centerline of the body. The starting point is to check to see where you are before permanently mounting the body.

From that point on, you can follow our descriptions here to ultimately find the right wheels and tires and achieve a balanced look for your ride.