How it works

TireFlows

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

Try
/R

Result

Diameter

29.13"

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

275/40R21+1.82%285/40R21+2.91%
Width 11.61 ″Rim 21 ″Dia. 29.13 ″4.06 ″Revs/Mile 692.4Circum. 91.5″
Diameter29.13"
Width11.61"
Sidewall4.06"
Circum.91.514"
Revs/Mile692.4

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