How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

2.24%

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

2.24%

Absolute Difference

0.69"

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
2020.4+0.4
3030.7+0.7
4040.9+0.9
5051.1+1.1
6061.3+1.3
7071.6+1.6
8081.8+1.8
Tire 1Dia. 30.74 ″Rim 21 ″4.87 ″Width 10.83 ″Revs/Mile 656.0Circum. 96.6″Tire 2Dia. 31.43 ″Rim 21 ″5.22 ″Width 10.43 ″Revs/Mile 641.6Circum. 98.8″
Tire 1
Specification
Tire 2
30.74"
Diameter
31.43"
10.83"
Width
10.43"
4.87"
Sidewall
5.22"
96.585"
Circum.
98.75"
656
Revs/Mile
641.6

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