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Common Tire Size Mistakes to Avoid

Most tire size errors come from exceeding overall diameter (OD) limits, selecting an incorrect load index, or creating drivetrain mismatches (especially on AWD vehicles).

Exceeding the ±3% overall diameter range

A change in overall diameter alters how far the tire travels per rotation. At highway speed, a ~3% difference can shift the speedometer by about 1.8 mph and affect how vehicle systems interpret wheel speed. While ±3% is commonly used as a replacement limit, some AWD setups operate within narrower tolerances. Learn more about the 3% Rule in our dedicated guide.

Using an incorrect load index (even within the same size)

The same tire size can carry different load ratings depending on construction. For example, a 265/70R17 in P-metric form may have a lower load index than an LT version of the same size. On trucks and SUVs, P-metric tires are also de-rated when used in light-truck service, further reducing their effective capacity. Choosing a tire with a lower load index than the original specification can lead to increased heat buildup under load and reduced safety margins.

Running mismatched diameters on AWD vehicles

Differences above ~1% in overall diameter force constant drivetrain compensation, accelerating wear in differentials and transfer cases. Note that even correctly sized tires can cause the same issue if tread depths are significantly mismatched — another reason AWD vehicles typically require full sets when replacing tires. Always verify the exact OD tolerances in your vehicle's owner's manual.

Using widths outside the approved rim range

Mounting a tire on a rim that is too narrow or too wide changes how the sidewalls sit and how the tread contacts the road. This can reduce stability, alter steering response, and lead to uneven wear across the tread. Always keep the tire size within its published rim width range.