How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

-1.42%

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

-1.42%

Absolute Difference

-0.45"

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
2019.7-0.3
3029.6-0.4
4039.4-0.6
5049.3-0.7
6059.1-0.9
7069-1
8078.9-1.1
Tire 1Dia. 31.61 ″Rim 20 ″5.81 ″Width 11.61 ″Revs/Mile 637.9Circum. 99.3″Tire 2Dia. 31.16 ″Rim 20 ″5.58 ″Width 12.40 ″Revs/Mile 647.2Circum. 97.9″
Tire 1
Specification
Tire 2
31.61"
Diameter
31.16"
11.61"
Width
12.4"
5.81"
Sidewall
5.58"
99.319"
Circum.
97.896"
637.9
Revs/Mile
647.2

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