How it works

TireFlows

Get diameter, speedometer impact, and alternate sizes — free, no signup.

Try
/R

Result

Diameter

31.81"

Calculated from size marking (math only) — not a fitment guarantee. How it works

Alternate Tire Sizes

Closest diameters (math only · same rim · within 3%)

Tap a size to compare it with your current size

295/45R21-1.11%315/45R21+1.11%285/50R21+1.3%325/40R21-1.79%285/45R21-2.23%325/45R21+2.23%295/50R21+2.54%315/40R21-2.78%
Width 12.01 ″Rim 21 ″Dia. 31.81 ″5.40 ″Revs/Mile 634.1Circum. 99.9″
Diameter31.81"
Width12.01"
Sidewall5.4"
Circum.99.925"
Revs/Mile634.1

How results are calculated

Tire dimensions are calculated from the metric size format (width / aspect ratio / rim diameter). Diameter, circumference, and revolutions per mile are derived mathematically — no fitment or vehicle data is used.

The 3% rule is a general reference for acceptable diameter difference, not a guarantee. Always check your vehicle manual or consult a tire professional.

How it works