How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

0.32%

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

0.32%

Absolute Difference

0.1"

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
2020.1+0.1
3030.1+0.1
4040.1+0.1
5050.2+0.2
6060.2+0.2
7070.2+0.2
8080.3+0.3
Tire 1Dia. 31.46 ″Rim 18 ″6.73 ″Width 11.22 ″Revs/Mile 641.0Circum. 98.8″Tire 2Dia. 31.56 ″Rim 18 ″6.78 ″Width 10.43 ″Revs/Mile 639.0Circum. 99.2″
Tire 1
Specification
Tire 2
31.46"
Diameter
31.56"
11.22"
Width
10.43"
6.73"
Sidewall
6.78"
98.849"
Circum.
99.158"
641
Revs/Mile
639

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