How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

1.58%

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

1.58%

Absolute Difference

0.5"

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
3030.5+0.5
4040.6+0.6
5050.8+0.8
6061+1
7071.1+1.1
8081.3+1.3
Tire 1Dia. 31.56 ″Rim 18 ″6.78 ″Width 10.43 ″Revs/Mile 639.0Circum. 99.2″Tire 2Dia. 32.06 ″Rim 18 ″7.03 ″Width 10.04 ″Revs/Mile 629.2Circum. 100.7″
Tire 1
Specification
Tire 2
31.56"
Diameter
32.06"
10.43"
Width
10.04"
6.78"
Sidewall
7.03"
99.158"
Circum.
100.704"
639
Revs/Mile
629.2

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