Rick's Free Auto Repair Advice

Tire contact patch

What is a tire contact patch?

A tire’s contact patch or footprint represents the amount of tire tread in contact with the road when the tire is inflated to the proper temperature.

Tire contact patch dimensions vary with load, air pressure, tire aspect ratio

A tire contact patch’s final dimensions depend on the inflation pressure, load and tire size/aspect ratio.

What is aspect ratio?

A tire’s size is given in three numbers: Width, ratio, and wheel size. So a tire size 205/70-14 is 205mm wide with a sidewall height of 143.5 (205mm X 70%= 143.5) to fit on a 14″ wheel.

A higher aspect ratio (taller sidewall) provides more comfort and better traction on wet and snowy roads. A smaller aspect ration, provides better dry traction and much more responsive handling.

In addition to handling and traction, lower aspect ratio tires have less rolling resistance due to their shorter sidewalls (less rubber to flex), and less rolling resistance means better MPG. That’s why many late model vehicles have low aspect ratio tires.

tire contact patch

The downside to low aspect ratio tire

With less space between the tire tread and the wheel (rim), the tire can’t handle as much impact. A medium sized pothole can result in a damaged wheel.

cracked wheel

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Posted on by Rick Muscoplat


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