How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

1.44%

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

1.44%

Absolute Difference

0.43"

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
4040.6+0.6
5050.7+0.7
6060.9+0.9
7071+1
8081.2+1.2
Tire 1Dia. 29.91 ″Rim 18 ″5.95 ″Width 10.83 ″Revs/Mile 674.3Circum. 94.0″Tire 2Dia. 30.34 ″Rim 18 ″6.17 ″Width 11.22 ″Revs/Mile 664.7Circum. 95.3″
Tire 1
Specification
Tire 2
29.91"
Diameter
30.34"
10.83"
Width
11.22"
5.95"
Sidewall
6.17"
93.963"
Circum.
95.324"
674.3
Revs/Mile
664.7

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