Information on Passenger Vehicle Tires
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Tire Ratings and Tire Safety

Wheel Size

This two-digit number is the wheel or rim diameter in inches. The diameter of the tire and wheel must match if you are replacing the tires but did you know you may be able and want to go up or down on your wheel sizes so long as you match the new tire correctly? As a matter of fact many manufactures provide larger wheel size options for many of their vehicles. A lot of people do it for the looks but there can be some real performance advantages that come along with changing your wheel size, especially when you change it up. The most common way this is done is by “upstepping”. Upstepping is done by increasing the wheel diameter and reducing the tire profile at the same time. This insures that the rolling radius remains constant and will negate the need to recalibrate the speedometer which would be otherwise thrown out of kilter.

possible sizes


A benefit of having the lower profile tires is in handling. The proportion of a shorter, flexible sidewall to the ridged wheel means an improved response and helps keep the tire square on the road for more stability especially in cornering. I have a few words of caution though. Going up an inch or two in wheel size will add weight to the car because the wheel material is heavier that the tire material that’s replaced. Auto enthusiasts call this “unsprung weight”. This can reduce gas mileage, acceleration and braking, so be aware of the new weight you’re going to be adding. Sometimes the “coolest” looking wheels are also the heaviest. A lower profile tire also “feels” the road more thereby reducing comfort levels.

If you go up a size on a wheel and tire but do not compensate with the profile then you will have to have your speedometer recalibrated because it was set for the particular rolling diameter of the original tire and wheel. You should also check with the manufacture to see if after market wheels or wheel sizes not recommended will void you vehicles warranty.

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