How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

1.63%

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

1.63%

Absolute Difference

0.49"

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
2020.3+0.3
3030.5+0.5
4040.7+0.7
5050.8+0.8
6061+1
7071.1+1.1
8081.3+1.3
Tire 1Dia. 30.05 ″Rim 18 ″6.02 ″Width 10.04 ″Revs/Mile 671.2Circum. 94.4″Tire 2Dia. 30.54 ″Rim 18 ″6.27 ″Width 9.65 ″Revs/Mile 660.4Circum. 95.9″
Tire 1
Specification
Tire 2
30.05"
Diameter
30.54"
10.04"
Width
9.65"
6.02"
Sidewall
6.27"
94.396"
Circum.
95.942"
671.2
Revs/Mile
660.4

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