Tire & Rim Guide
Tires and rims can make or break your car's look and performance. Whether you're just looking for a stock replacement steel wheel and basic tire or 29-inch show wheels made of polished armadillo hide, you'll get nowhere fast without knowing the basics.
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Tire Type
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Tires come in several varieties with different names depending on where you buy them. Standard all-season tires provide acceptable traction in the wet and dry, and a modicum of grip in ice and snow. All-terrain tires offer less grip on dry surfaces but do a better job of digging into soft surfaces like sand and mud. Winter tires handle ice and snow at the expense of dry road handling and performance tires are generally designed to provide more grip on dry roads at the expense of some comfort and (often) wet-road traction.
Tire Compound
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Tire compounds range between rock-hard and putty-soft. Very hard tires offer reduced rolling resistance (for better fuel economy) and take a long time to wear out but don't handle well. Very soft tires can stick to the road like glue (especially when hot) but tend to wear out very quickly.
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Tire Aspect Ratio
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Aspect ratio, defined as the tire sidewall height divided by width, has a huge impact on performance. Tires with very tall sidewalls (like 75, 85 and 95 series) provide a lot of cushion and deformability for a comfortable ride and off-road traction, but those tall sidewalls don't do a very good job of keeping the tread centered under the rim. Very short sidewalls (like 15, 25 and 35 series) offer very sharp steering response and predictable handling at the limit of adhesion but do so at the expense of ride comfort.
Rim Material
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Most stock rims are steel, which offers strength in abundance but is very heavy. Heavy rims make for slower acceleration and decreased suspension response (causing sluggish handling and a poor ride), which is why many aftermarket rims are made of aluminum. Cast aluminum wheels (which are made by pouring molten aluminum into a mold) are light and cheap, but aren't very strong. Forged wheels (made by hammering hot or cold aluminum blocks into shape) are far stronger than cast wheels, but are often two to three times more expensive.
Rim Offset
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One of the most important aspects to rim fitment is offset. Offset is defined as the distance between the back of the wheel's mounting flange relative to the wheel's centerline. If the flange is even with the centerline of the rim, it's said to have "zero offset." If the mounting flange is closer to the outside of the rim, it has positive offset (which tucks the tire in closer to the car body); a flange closer to the back has negative offset (which pushes the wheel outward). For example, a mounting flange two inches forward has a two-inch positive offset; one two inches back has a two-inch negative offset. Those "deep dish" rims you see on many rear wheel drive sports cars typically exhibit several inches of negative offset.
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References
- Photo Credit sports car rim image by Lario Tus from Fotolia.com
