How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

1.33%

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

1.33%

Absolute Difference

0.41"

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
2020.3+0.3
3030.4+0.4
4040.5+0.5
5050.7+0.7
6060.8+0.8
7070.9+0.9
8081.1+1.1
Tire 1Dia. 30.81 ″Rim 20 ″5.40 ″Width 12.01 ″Revs/Mile 654.7Circum. 96.8″Tire 2Dia. 31.22 ″Rim 20 ″5.61 ″Width 11.22 ″Revs/Mile 646.0Circum. 98.1″
Tire 1
Specification
Tire 2
30.81"
Diameter
31.22"
12.01"
Width
11.22"
5.4"
Sidewall
5.61"
96.783"
Circum.
98.082"
654.7
Revs/Mile
646

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