How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

-2.35%

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

-2.35%

Absolute Difference

-0.77"

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
2019.5-0.5
3029.3-0.7
4039.1-0.9
5048.8-1.2
6058.6-1.4
7068.4-1.6
8078.1-1.9
Tire 1Dia. 32.78 ″Rim 20 ″6.39 ″Width 11.61 ″Revs/Mile 615.3Circum. 103.0″Tire 2Dia. 32.01 ″Rim 20 ″6.00 ″Width 12.01 ″Revs/Mile 630.1Circum. 100.6″
Tire 1
Specification
Tire 2
32.78"
Diameter
32.01"
11.61"
Width
12.01"
6.39"
Sidewall
6"
102.968"
Circum.
100.556"
615.3
Revs/Mile
630.1

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