“The Four Horsemen:” Let’s say you’ve got your eye on a set of smart-looking aftermarket wheels. What’s next? You need to make sure the wheels will fit your vehicle. This is a bit complicated, but if you follow the guidelines below you should end up with wheels that do the job.
Four characteristics determine wheel fit. They are: 1) size (wheel diameter and rim width); 2) bolt circle; 3) load rating; and 4) offset. Let’s look at each in turn.
1) Size: Select a wheel size appropriate for the desired tire and load-carrying capacity. A given tire size can fit a range of rim widths; in other words, a P265/75R15 tire can be used on a 7- to 9.5-inch wide rim. The rim width will affect the appearance of the tire by changing the sidewall profile.
2) Bolt Circle: A wheel has a number of evenly spaced stud or bolt holes. The bolt circle is the diameter of an imaginary circle that runs through the bolt hole centers. You measure from the center of one bolt hole, across the center of the hub face, to a point that intersects the imaginary circle drawn through the bolt hole centers. This measurement is usually stated in inches or millimeters.
3) Load Rating: The maximum load rating of the tire, wheel, and axle must be compatible. A bigger wheel does not always mean a bigger load rating. For example, several Alcoa 16x7J wheels carry maximum load ratings of 2,600 pounds, yet other Alcoa wheels the same size are load rated to 3,040 pounds. The load rating on your new customized equipment should be at least as high as the original equipment wheel and tire.
4) Offset: Of the four fitment characteristics, this is by far the most complex. Offset is the distance from the wheel mounting surface (mounting pad) to the centerline of the rim. Zero offset means the rim centerline is in line with the mounting surface. Negative offset means the centerline is outboard of the mounting surface; positive offset means the centerline is inboard of the mounting surface. Changing offset too much from stock may accelerate tire wear, impede steering response, and hamper stability.
“It’s a good idea to match the original equipment wheel backspace when going to wider tires. This helps prevent fitment problems,” Simpson says. “Getting the right offset for your particular application is 90 percent of successful custom wheel fitment. Offset is crucial to avoid clearance problems with fenders, struts, anti-sway bars, brake calipers, and other suspension parts. Maintain the wheel offset as close to stock as possible, especially on the front wheels.”
Six Steps to Success: Simpson recommends a six-step procedure that any professional installer can do for you. Following this guide will ensure that the new wheels fit the tires, and the new wheel-tire combination fits the truck.
1) Place the truck on a lift rack and raise it off the floor. Remove one front wheel.
2) Clean the mounting surface on the hub with a wire brush and remove any retainer (spring) clips.
3) Hold the aftermarket wheel (no tire) on the hub and check for a flush mount. The mounting surface of the wheel must fit flush to the hub mounting surface. The back side of the wheel must not rest against any obstructions such as the brake caliper, suspension components, balance weights, or rivets.
4) Install three lug nuts and hand tighten. Rotate the wheel and fully turn the steering wheel in both directions to ensure complete clearance.
5) Repeat the above steps on the rear of the vehicle. (The one exception is that you won’t need to turn the steering wheel.)
6) As a final check, mount the tires to the new wheels and install all four on the truck. Lower the truck to the floor. This will put the vehicle in a “true” ride position because the weight of the truck will settle on the tires, causing them to spread closer to underbody components. Do another check.