How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

-0.68%

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

-0.68%

Absolute Difference

-0.21"

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
2019.9-0.1
3029.8-0.2
4039.7-0.3
5049.7-0.3
6059.6-0.4
7069.5-0.5
8079.5-0.5
Tire 1Dia. 31.04 ″Rim 20 ″5.52 ″Width 10.04 ″Revs/Mile 649.7Circum. 97.5″Tire 2Dia. 30.83 ″Rim 20 ″5.41 ″Width 10.83 ″Revs/Mile 654.2Circum. 96.8″
Tire 1
Specification
Tire 2
31.04"
Diameter
30.83"
10.04"
Width
10.83"
5.52"
Sidewall
5.41"
97.525"
Circum.
96.845"
649.7
Revs/Mile
654.2

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