How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

1.37%

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

1.37%

Absolute Difference

0.41"

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
3030.4+0.4
4040.5+0.5
5050.7+0.7
6060.8+0.8
7071+1
8081.1+1.1
Tire 1Dia. 29.98 ″Rim 21 ″4.49 ″Width 11.22 ″Revs/Mile 672.8Circum. 94.2″Tire 2Dia. 30.39 ″Rim 21 ″4.69 ″Width 10.43 ″Revs/Mile 663.6Circum. 95.5″
Tire 1
Specification
Tire 2
29.98"
Diameter
30.39"
11.22"
Width
10.43"
4.49"
Sidewall
4.69"
94.174"
Circum.
95.472"
672.8
Revs/Mile
663.6

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