How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

2%

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%

Absolute Difference

0.61"

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
2020.4+0.4
3030.6+0.6
4040.8+0.8
5051+1
6061.2+1.2
7071.4+1.4
8081.6+1.6
Tire 1Dia. 30.43 ″Rim 20 ″5.22 ″Width 10.43 ″Revs/Mile 662.7Circum. 95.6″Tire 2Dia. 31.04 ″Rim 20 ″5.52 ″Width 10.04 ″Revs/Mile 649.7Circum. 97.5″
Tire 1
Specification
Tire 2
30.43"
Diameter
31.04"
10.43"
Width
10.04"
5.22"
Sidewall
5.52"
95.608"
Circum.
97.525"
662.7
Revs/Mile
649.7

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