How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

2.81%

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

2.81%

Absolute Difference

0.82"

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
2020.6+0.6
3030.8+0.8
4041.1+1.1
5051.4+1.4
6061.7+1.7
7072+2
8082.2+2.2
Tire 1Dia. 29.18 ″Rim 19 ″5.09 ″Width 9.25 ″Revs/Mile 691.2Circum. 91.7″Tire 2Dia. 30.00 ″Rim 19 ″5.50 ″Width 8.46 ″Revs/Mile 672.2Circum. 94.3″
Tire 1
Specification
Tire 2
29.18"
Diameter
30"
9.25"
Width
8.46"
5.09"
Sidewall
5.5"
91.663"
Circum.
94.26"
691.2
Revs/Mile
672.2

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