How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

2.5%

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

2.5%

Absolute Difference

0.79"

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
4041+1
5051.2+1.2
6061.5+1.5
7071.7+1.7
8082+2
Tire 1Dia. 31.61 ″Rim 20 ″5.81 ″Width 11.61 ″Revs/Mile 637.9Circum. 99.3″Tire 2Dia. 32.40 ″Rim 20 ″6.20 ″Width 12.40 ″Revs/Mile 622.4Circum. 101.8″
Tire 1
Specification
Tire 2
31.61"
Diameter
32.4"
11.61"
Width
12.4"
5.81"
Sidewall
6.2"
99.319"
Circum.
101.793"
637.9
Revs/Mile
622.4

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