How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

1.79%

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

1.79%

Absolute Difference

0.53"

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
3030.5+0.5
4040.7+0.7
5050.9+0.9
6061.1+1.1
7071.3+1.3
8081.4+1.4
Tire 1Dia. 29.65 ″Rim 20 ″4.82 ″Width 9.65 ″Revs/Mile 680.3Circum. 93.1″Tire 2Dia. 30.18 ″Rim 20 ″5.09 ″Width 9.25 ″Revs/Mile 668.3Circum. 94.8″
Tire 1
Specification
Tire 2
29.65"
Diameter
30.18"
9.65"
Width
9.25"
4.82"
Sidewall
5.09"
93.135"
Circum.
94.804"
680.3
Revs/Mile
668.3

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