How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

2.36%

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

2.36%

Absolute Difference

0.71"

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
3030.7+0.7
4040.9+0.9
5051.2+1.2
6061.4+1.4
7071.7+1.7
8081.9+1.9
Tire 1Dia. 30.10 ″Rim 20 ″5.05 ″Width 11.22 ″Revs/Mile 670.1Circum. 94.6″Tire 2Dia. 30.81 ″Rim 20 ″5.40 ″Width 12.01 ″Revs/Mile 654.7Circum. 96.8″
Tire 1
Specification
Tire 2
30.1"
Diameter
30.81"
11.22"
Width
12.01"
5.05"
Sidewall
5.4"
94.557"
Circum.
96.783"
670.1
Revs/Mile
654.7

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