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All About Tire/Wheel Combination Calculators

Wheels are not tires, despite popular opinion. The part trio of hub, spokes and rim work together to fashion one wheel. The hub attaches the wheel to the vehicle's suspension and is located in the center of the wheel. The spokes branch out from the hub, which attach the hub to the rim. The rim is the outer portion of the wheel that holds the tire.

Tires are made of a tread, sidewall, body plies, inner liner, steel belts, and a bead bundle. Cap plies and edge covers are optional. The tread is made of natural and synthetic rubber. The pattern on the tread gives traction to the tire that keeps it from spinning wildly on the road, especially in inclement weather.

It is imperative that mechanics and automakers fit the correct wheel to the suspension and find the correct tire measurement to fit the wheel so that the tire handles correctly and looks right on the vehicle. Tires are sized by section width, aspect ratio, and wheel diameter.

If a tire is listed as size 215/40-17, the 215 is the section width, the 40 is the aspect ratio and 17, the wheel diameter.

  • Section width: the tire width at the sidewalls measured in millimeters when mounted. Tread and rim width are not included in this measurement.
  • Aspect ratio: sidewall height. This is a percentage of the section width or section width times the aspect ratio will give the sidewall height.
  • Wheel diameter: measured in inches at the tire mounting surface.

When buying new wheels and tires, keep the measurements the same as the factory standards or there may be problems in handling, rubbing, or aesthetics.

In order to find the best wheels and tires for a vehicle, mathematically-inclined consumers and mechanics can follow these formulas:


Tire height = wheel diameter + (2 x (section width / 25.4) X (aspect ratio / 100))

Rollout = tire height X PI

Wheel rpm = (vehicle speed/60) X (5280/(rollout / 12))

Engine rpm = wheel rpm x rear gear ratio x transmission gear ratio

It's easiest however to use a simple calculator called the tire/wheel combination calculator.

By entering some initial information into a wheel/tire combination calculator, such as the current and planned section width, tire aspect ratio, wheel diameter, width and offset, the calculator will give the following current and planned results: tire height, ride height difference, tire width difference, tire rollout, wheel/tire aspect ratio, wheel diameter, offset and width differences, wheel inboard and outboard increases, tire and wheel inboard and outboard increases, wheel rpms at 'x' mph, actual speed with new tire/wheel combination, speedometer error percentage with the new combination, the engine rpms with rear gear and transmission gear ratio and the effective gear ratio with the new tire and wheel combination.

Tire/Wheel Combination Calculator 1 Formulas and calculator.

Tire/Wheel Combination Calculator 2 Calculator only using current and planned tire and wheel information,

Tire/Wheel Compensation Calculator Speedometer correction calculator when the tire/wheel combination is not factory specific.

Martindale's Automotive Calculators Complete automotive calculators, manuals, and more.

Choosing the Best Tires for Your Wheels Details considerations as tread life, speed rating and ride quality.

These figures will give an idea of how the old wheels and tires compare to the new wheels and tires and how they will affect the performance and look of your vehicle.

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