How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

1.31%

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

1.31%

Absolute Difference

0.43"

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
2020.3+0.3
3030.4+0.4
4040.5+0.5
5050.7+0.7
6060.8+0.8
7070.9+0.9
8081+1
Tire 1Dia. 32.78 ″Rim 20 ″6.39 ″Width 11.61 ″Revs/Mile 615.3Circum. 103.0″Tire 2Dia. 33.21 ″Rim 20 ″6.60 ″Width 12.01 ″Revs/Mile 607.3Circum. 104.3″
Tire 1
Specification
Tire 2
32.78"
Diameter
33.21"
11.61"
Width
12.01"
6.39"
Sidewall
6.6"
102.968"
Circum.
104.328"
615.3
Revs/Mile
607.3

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