How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

-2.16%

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

-2.16%

Absolute Difference

-0.68"

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
2019.6-0.4
3029.4-0.6
4039.1-0.9
5048.9-1.1
6058.7-1.3
7068.5-1.5
8078.3-1.7
Tire 1Dia. 31.46 ″Rim 18 ″6.73 ″Width 11.22 ″Revs/Mile 641.0Circum. 98.8″Tire 2Dia. 30.78 ″Rim 18 ″6.39 ″Width 11.61 ″Revs/Mile 655.3Circum. 96.7″
Tire 1
Specification
Tire 2
31.46"
Diameter
30.78"
11.22"
Width
11.61"
6.73"
Sidewall
6.39"
98.849"
Circum.
96.684"
641
Revs/Mile
655.3

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