How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

-2.47%

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

-2.47%

Absolute Difference

-0.78"

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
5048.8-1.2
6058.5-1.5
7068.3-1.7
8078-2
Tire 1Dia. 31.61 ″Rim 20 ″5.81 ″Width 11.61 ″Revs/Mile 637.9Circum. 99.3″Tire 2Dia. 30.83 ″Rim 20 ″5.41 ″Width 10.83 ″Revs/Mile 654.2Circum. 96.8″
Tire 1
Specification
Tire 2
31.61"
Diameter
30.83"
11.61"
Width
10.83"
5.81"
Sidewall
5.41"
99.319"
Circum.
96.845"
637.9
Revs/Mile
654.2

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