How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

2.35%

Safety Rating

Safe

Within the recommended 3% safety margin.

The 3% rule is a common reference — not vehicle-specific advice. How it works

Speedometer Error

2.35%

Absolute Difference

0.73"

Speedometer

Assumes Tire 1 is what the speedometer is calibrated for. Shows approximate actual speed if you switch to Tire 2.

Reading (mph)Actual (mph)Difference
2020.5+0.5
3030.7+0.7
4040.9+0.9
5051.2+1.2
6061.4+1.4
7071.6+1.6
8081.9+1.9
Tire 1Dia. 31.10 ″Rim 21 ″5.05 ″Width 11.22 ″Revs/Mile 648.5Circum. 97.7″Tire 2Dia. 31.83 ″Rim 21 ″5.41 ″Width 10.83 ″Revs/Mile 633.7Circum. 100.0″
Tire 1
Specification
Tire 2
31.1"
Diameter
31.83"
11.22"
Width
10.83"
5.05"
Sidewall
5.41"
97.699"
Circum.
99.987"
648.5
Revs/Mile
633.7

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