How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

-1.19%

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

-1.19%

Absolute Difference

-0.38"

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
2019.8-0.2
3029.6-0.4
4039.5-0.5
5049.4-0.6
6059.3-0.7
7069.2-0.8
8079-1
Tire 1Dia. 31.83 ″Rim 21 ″5.41 ″Width 10.83 ″Revs/Mile 633.7Circum. 100.0″Tire 2Dia. 31.45 ″Rim 21 ″5.23 ″Width 11.61 ″Revs/Mile 641.2Circum. 98.8″
Tire 1
Specification
Tire 2
31.83"
Diameter
31.45"
10.83"
Width
11.61"
5.41"
Sidewall
5.23"
99.987"
Circum.
98.812"
633.7
Revs/Mile
641.2

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