How to Measure Wheel Backspacing
Wheel backspacing is a CRUCIAL measurement, if you're planning to install new tires and wheels on your collector vehicle. This measurement determines proper fitment of your tires and wheels, but measuring wheel backspacing is very quick and easy. We'll walk you through it, and also give you some insight on how to measure your vehicle for proper tire and wheel fitment. Let's get right into it!
How to Measure Wheel Width
Before measuring backspacing, it's important to know the width of your wheel. The width measurement is taken from the bead area, and does NOT include the outer flanges.
In the case of this 15x8-inch Smoothie wheel, you can see that we're measuring from bead to bead. If we were to measure the entire width, it would be closer to 9 inches, which not the correct measurement, but it is important to note that total width when we measure backspacing.
How to Measure Wheel Backspacing
With the wheel turned over, we have easy access to the back side. Backspacing is the measurement between the mounting surface of the wheel and the edge of the rim flange (not the bead). You can measure backspacing with a straight edge and a tape measure, or in the case of our photo, two straight edge rulers. One straight edge will lay across the outer edge of the wheel, to keep you from having to estimate how far the rim comes out. Remember, backspacing variances of a quarter-inch can make or break the fitment. Once the straight edge is laying across the wheel, measure from the mounting surface of the wheel to the straight edge. Side note: It does seem confusing that we measure wheel width from bead to bead, but we measure backspacing to the edge of the rim flange, but that's the industry standard, so we're rolling with it.
What's the Difference Between Backspacing and Offset?
Wheel measurements can be confusing, and one thing we run into on a regular basis is the question regarding backspacing vs. offset. To answer this question, backspacing is the measurement from the mounting surface to the outer rim flange and offset is distance away from "center". So, in the case of a 15x8-inch wheel, a ZERO Offset wheel would have 4.5 inches of backspacing. The wheel's center section is "centered" insde the rim, so there is 4.5 inches to the front side of the rim and 4.5 inches to the back side. Remember when we said that a 15x8 inch wheel actually measures about 9 inches total? That's where this comes into play.
Other imporant notes are the positive offset equals MORE backspacing, like the wheels you see on modern cars, where the face of the wheel is nearly flush with the outer edge. This started happening in the 1980's and continues to be popular. Negative offset equals LESS backspacing, giving you a deep dish look. At Coker Tire, all of our wheel measurements are listed as backspacing, giving you the easiest way to calculate proper tire and wheel fitment.
How to Measure Your Vehicle for Custom Tire and Wheel Fitment
Knowing how to measure wheel backspacing is crucial, but what's even more important is knowing what will fit your vehicle. For this, we can once again rely on a couple of straight edge rulers to help us determine the maximum about of backspacing and front spacing our vehicle can handle.
No matter what type of car or truck you're working on, these principles apply. First, the vehicle needs to be supported with jacks or jackstands, so that the weight of the vehicle is resting on its suspension. In other words, you don't want the suspension to be drooping. Next, grab your measuring tape or ruler and base all of your measurements off of the surface where the wheel is going to eventually mount.
Measure from the straight edge over to the inside portions of the inner fender, taking consideration for any obvious clearance issues, like shock mounts, tie rod ends or other items. Then, measure from the straight edge to the outer side, where fender lips come into play.
The front of the vehicle is especially important, beceause you'll need to measure with the steering straight, as well as full lock in both directions. This is even more important if you're looking to fit the maximum width underneath a lowered vehicle. Out back, the same principles are in place, but it's more of a static measurement since the rear axle doesn't steer. Be sure to write down your measurements and always allow for at least an inch of sidewall bulge, unless you're planning to run low profile tires. Also take into consideration that the suspension will flex at times, during driveway transitions.
In the case of the photo above, the measurements showed an total area of six inches on the back side and eight inches on the front side of the mounting surface. Obviously, we cannot install a 14-inch wide wheel on this truck, so after we decuct an inch on each side for sidewall bulge and an inch on each side for suspension flex, we've determined that we can safely run a 15x10-inch wheel with 4 to 4.5 inches of backspacing. If you have questions about tire and wheel fitment our experts are glad to help you figure out the right fit for your vehcile.