Wheel Tech

Other than saying, "they look cool" or maybe, "they're really light," how much do we really know about our wheels? Words like "forged", "cast", "billet" and, if you're old-skool, F.O.B. "mag wheels", come to mind. But do we really know what they mean? Do we know an offset from a bolt pattern? And why do some wheels have nine holes instead of four or five? We'll answer these questions and more so that you can check out this month's Wheel Buyer's guide armed with a little bit of knowledge up your sleeve.

Wheel Sizing
Wheels come in all shapes and sizes. Duh, right? Not really. Sure, we all know about 15s, 16s, 17s and the ever-elusive chrome dubs (20s). And we're all familiar with the myriad of widths, too - from the anemic 5.5-in steel stockers to the 13-in street rockers. But what's with all that offset and backspace crap? Why does backspace matter? And how is it measured?

For starters, imagine you're laying on the ground and a car is coming at you head on, right about to roll over you. If you were to draw an imaginary line down the center of the wheel that was rolling over your new kicks, then you'd have a pretty good idea of what "offset" is. See the big surface area that actually touches the wheel to the car? No? OK, pretend that you have x-ray vision and you can see through the tire and through the center of the rim. A positive offset (represented by an "ET+") means that the mounting surface of the wheel is closer to the outside face of the rim and, consequently, the inside of the rim is closer to the inner fender well. It may seem like reverse logic, but think about it for a while and you'll get it. On the other hand, a negative offset is the exact reverse situation and creates what some tuners affectionately refer to as "fat lip" (think wide-body cars with gargantuan 10-in wide wheels in the rear). The negative offset is usually reserved for the larger cars, rear and all-wheel drivers, and cars set up with wide bodies for drifting and such. The benefit of negative offset comes from the wider track, but can be detrimental if mounted improperly with short lug nuts. Remember, not all cars and suspension setups can (or should) run negative offsets, so "plug and play" doesn't apply here.

The distance from the mounting surface of the wheel to the inner edge of the rim is known as "backspace." This is useful information if you're going to run a big brake setup or if you're trying to precisely calculate a rim/tire combination for your specific track setup. Remember that the amount of backspace also tells you how much rubbage you'll have against inner fenders, control arms and other such fender-well and undercarriage goodies. Don't forget to take into account the plethora of available widths and sidewall ratios of the thousands of tires available on the market before you decide on the "perfect rim" for your application.