How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

2.51%

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

2.51%

Absolute Difference

0.8"

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
6061.5+1.5
7071.8+1.8
8082+2
Tire 1Dia. 31.81 ″Rim 21 ″5.40 ″Width 12.01 ″Revs/Mile 634.1Circum. 99.9″Tire 2Dia. 32.61 ″Rim 21 ″5.81 ″Width 11.61 ″Revs/Mile 618.4Circum. 102.5″
Tire 1
Specification
Tire 2
31.81"
Diameter
32.61"
12.01"
Width
11.61"
5.4"
Sidewall
5.81"
99.925"
Circum.
102.46"
634.1
Revs/Mile
618.4

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