Wheel And Tire Sizes - Measuring Up

How To Select The Correct Wheel And Tire Size The First Time

Damon Lee Jun 1, 2000 0 Comment(s)
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Most enthusiasts know that wheels and tires can make or break a street machine. Whether you're putting big billet hoops and low-profile radials on a custom Impala or rally wheels and resto-style Wide Ovals on a restored Chevelle, the size and fit of the rolling stock has to be correct for the finished car to look, sit, and drive right.

While finding the right tire and wheel size for a stock-style restoration or mild street machine is typically pretty easy, squeezing large-diameter, extra-wide rims and rubber into the confines of a stock Chevy wheel opening can be a challenge. Heck, even putting moderately sized rolling stock on a lowered Bow-Tie can be tricky. And unfortunately, too many enthusiasts rely on guesstimates and second-hand statistics when ordering wheels and tires for their cars, only to find that they don't fit right when mounted in place.

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We at Super Chevy know firsthand what a hassle it can be to end up with improperly sized wheels or tires for that prized project car. So we've put together this guide to help you get the right dimensions the first time. The following photos, diagrams, definitions, and suggestions should arm you with the knowledge you need to make an informed purchase. But keep in mind that we can't make the final selection for you. It's up to you to take measurements, ask questions, and make the final determination on which wheels and tires are right for your ride.

Wheel Words
When preparing to purchase a new set of custom wheels, it's extremely important to take accurate measurements to determine which size you need. The following diagram and definitions show the dimensions that wheel manufacturers need to know. Of these, bolt pattern, rim width, and rim diameter are the most obvious and important. In addition, backspacing (or rear spacing) is a vital dimension to know.

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Bolt Pattern: The pattern determined by the number of bolt holes (or lug holes) and the diameter of the bolt circle.

Hub Diameter: Also called the center bore, this is the measurement of the hole at the center of the wheel.

Offset: The distance from the centerline of the wheel to the mounting surface of the wheel. Measured in millimeters.

Negative Offset: When the back of the mounting pad is closer to the inside of the wheel; when the mounting surface is inboard of the rim centerline.

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Positive Offset: When the back of the mounting pad is closer to the street side of the wheel; when the mounting surface is outboard of the rim center line.

Rear Spacing: Also called backspacing. The distance from the backside of the wheel mounting pad to the outside of the rim flange.

Tire Terms
It's also important to consider the dimensions of your tires when selecting a wheel-and-tire package. To do this, you'll want to know some basic specifications on the tires. The following measurements should help you out, with the most important considerations being aspect ratio, section width, and overall diameter.

Aspect Ratio: The ratio of the tire's section height to its section width. Typically calculated by dividing the section height by the section width and multiplying that number by 100.

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