How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

-0.79%

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

-0.79%

Absolute Difference

-0.25"

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
2019.8-0.2
3029.8-0.2
4039.7-0.3
5049.6-0.4
6059.5-0.5
7069.4-0.6
8079.4-0.6
Tire 1Dia. 31.46 ″Rim 18 ″6.73 ″Width 11.22 ″Revs/Mile 641.0Circum. 98.8″Tire 2Dia. 31.21 ″Rim 18 ″6.60 ″Width 12.01 ″Revs/Mile 646.2Circum. 98.0″
Tire 1
Specification
Tire 2
31.46"
Diameter
31.21"
11.22"
Width
12.01"
6.73"
Sidewall
6.6"
98.849"
Circum.
98.045"
641
Revs/Mile
646.2

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