How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

2.62%

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

2.62%

Absolute Difference

0.86"

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
2020.5+0.5
3030.8+0.8
4041+1
5051.3+1.3
6061.6+1.6
7071.8+1.8
8082.1+2.1
Tire 1Dia. 32.78 ″Rim 20 ″6.39 ″Width 11.61 ″Revs/Mile 615.3Circum. 103.0″Tire 2Dia. 33.64 ″Rim 20 ″6.82 ″Width 12.40 ″Revs/Mile 599.5Circum. 105.7″
Tire 1
Specification
Tire 2
32.78"
Diameter
33.64"
11.61"
Width
12.4"
6.39"
Sidewall
6.82"
102.968"
Circum.
105.689"
615.3
Revs/Mile
599.5

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