Tech Article: How BMW Suspension Upgrades Effect Wheel Fitment

Each BMW chassis rolls off the assembly line with a different amount of available real estate under the fender arches, meaning some vehicles will have more limitations than others. Typically, the fenders on a non-M 3-Series chassis start out with dramatically less space in comparison to the M3 with factory flared fenders. As a result, it is increasingly more difficult for non-M cars to accommodate a set of wide wheels and race rubber.

Aside from how an auto manufacturer designs the body work of a given vehicle, one of the most important contributing factors in determining how much space you have to work with is the genetic makeup of your OEM or aftermarket suspension configuration. Just as the performance capabilities drastically vary from one suspension to another, each impedes wheel and tire clearance differently due to a variance in spring shape (conical vs linear), spring length, strut body diameter, whether or not helper/tender springs are present, and ultimately the overall stack height.

If maximizing wheel and tire width is important to you, it is imperative to consider the physical size of your current suspension setup prior to purchasing a new set of wheels and tires. This is also an important factor to consider upon upgrading your suspension. While you may not have immediate plans to push the limits of wheel and tire width, we encourage you to plan for the future.

The E46 M3 photo above depicts the front and rear suspension configuration used on the following models: E30, E36 & Z3, E46, E8x 1-Series & Z4, E9x, F3x, & F8x.

Taking a closer look at the photo above, we can clearly see how the overall suspension layout varies between the front and rear of the car. When comparing the differences in these two suspension configurations, it becomes clear as to why so much more emphasis is placed on front clearance as opposed to the rear. The factory BMW suspension consists of a coilover (coil spring over shock) design in the front, and a “divorced” spring and shock configuration in the rear. This “divorced” configuration places the springs inboard on the rear control arms, leaving ample clearance for a wider rear wheel and tire setup. A vast majority of enthusiasts choose to keep a divorced rear suspension configuration, even in cases where the car is being heavily modified for track work.