Since we tuck our rims when our trucks are laid out, this adds an extra variable to the equation. Using these tips, you can correctly measure for the wheel fitment that best suits your suspension setup and lowered attitude of the specific truck. While we were recently at Suspension Dimension in San Bernardino, California, we decided to check out our S-10 to see what wheel fitment would work best with the truck.
Since we hadn't correctly measured for wheels in the past, we've wasted plenty of tires and the backsides of custom wheels. Don't let this happen to you. With enough information, you'll be able to order the right offset wheels for your truck, run shocks more effectively with a 'bagged ride, and have a more driveable vehicle.
Backspacing, Frontspacing & Offset
The relationship between a wheel's mounting pad or surface and the rim itself can be a confusing subject for many truckers. The terms backspacing and frontspacing refer to where the wheel is placed relative to the mounting pad. The terms are not often used together because one measurement will take care of both distances.
If a wheel has a certain measured backspacing, the rest of the distance of the width of the rim is obviously frontspacing. However, backspacing is the most commonly used description of a wheel's spacing. Backspacing is simply the distance from the back of a wheel's mounting pad to the back edge of the rim. Conversely, frontspacing is the distance of the front side of the rim relative to the back of the mounting pad.
Offset is the distance of the mounting pad from the true lateral center of the wheel. A wheel with the mounting pad centered laterally in the wheel hoop has zero offset. When a wheel has its mounting pad closer to the suspension, it has positive offset.
If the mounting pad center is moved out closer to the outside of the vehicle, it has negative offset. Trucks do not typically employ negative offset wheels as frequently as front-wheel-drive cars, and almost all older trucks have positive offset wheels.
First, we jacked up the vehicle...
First, we jacked up the vehicle and supported it for safety.
Then we pulled the wheel and...
Then we pulled the wheel and placed it on one side to begin making measurements to determine the best wheel for your truck.
We decided to use the crudest...
We decided to use the crudest items available to measure to make things simple. To find the drop line from the fender edge, we hung a plumb bob from the inner edge of the fender.
We carefully measured the...
We carefully measured the distance from the face of the wheel-mounting surface to the point at which the plumb bob hung and subtracted about 1 to 1-1/2 inches (the safety zone) and recorded our findings. This represented the maximum space available outboard for wheels.
We measured again from the...
We measured again from the backside of the rotor and added this number to the previous measurement we made to find the recommended minimum width for wheels.
Using a straightedge, we measured...
Using a straightedge, we measured back from the safety zone to figure backspacing. We also measured from the mounting pad rearward to the width of the wheel we wanted to use.
Once we decided on the wheels,...
Once we decided on the wheels, we checked fitment by turning the wheel from lock to lock and rotated it to make sure the wheel cleared all suspension components without contacting them.
A simple final check revealed...
A simple final check revealed to us that we could run a wheel with less backspacing, thereby creating more room on the chassis for the installation of relocated shocks for our 'bagged truck.