How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

-0.07%

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

-0.07%

Absolute Difference

-0.02"

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
20200
30300
40400
50500
60600
70700
8079.9-0.1
Tire 1Dia. 30.05 ″Rim 18 ″6.02 ″Width 10.04 ″Revs/Mile 671.2Circum. 94.4″Tire 2Dia. 30.03 ″Rim 18 ″6.01 ″Width 9.25 ″Revs/Mile 671.7Circum. 94.3″
Tire 1
Specification
Tire 2
30.05"
Diameter
30.03"
10.04"
Width
9.25"
6.02"
Sidewall
6.01"
94.396"
Circum.
94.334"
671.2
Revs/Mile
671.7

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