How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

1.25%

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

1.25%

Absolute Difference

0.39"

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
2020.2+0.2
3030.4+0.4
4040.5+0.5
5050.6+0.6
6060.7+0.7
7070.9+0.9
8081+1
Tire 1Dia. 31.22 ″Rim 20 ″5.61 ″Width 11.22 ″Revs/Mile 646.0Circum. 98.1″Tire 2Dia. 31.61 ″Rim 20 ″5.81 ″Width 11.61 ″Revs/Mile 637.9Circum. 99.3″
Tire 1
Specification
Tire 2
31.22"
Diameter
31.61"
11.22"
Width
11.61"
5.61"
Sidewall
5.81"
98.082"
Circum.
99.319"
646
Revs/Mile
637.9

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