How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

-0.19%

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

-0.19%

Absolute Difference

-0.06"

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
20200
3029.9-0.1
4039.9-0.1
5049.9-0.1
6059.9-0.1
7069.9-0.1
8079.8-0.2
Tire 1Dia. 31.56 ″Rim 18 ″6.78 ″Width 10.43 ″Revs/Mile 639.0Circum. 99.2″Tire 2Dia. 31.50 ″Rim 18 ″6.75 ″Width 9.65 ″Revs/Mile 640.2Circum. 99.0″
Tire 1
Specification
Tire 2
31.56"
Diameter
31.5"
10.43"
Width
9.65"
6.78"
Sidewall
6.75"
99.158"
Circum.
98.973"
639
Revs/Mile
640.2

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