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

0.83"

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. 29.57 ″Rim 18 ″5.79 ″Width 9.65 ″Revs/Mile 681.9Circum. 92.9″Tire 2Dia. 30.40 ″Rim 18 ″6.20 ″Width 8.86 ″Revs/Mile 663.4Circum. 95.5″
Tire 1
Specification
Tire 2
29.57"
Diameter
30.4"
9.65"
Width
8.86"
5.79"
Sidewall
6.2"
92.912"
Circum.
95.509"
681.9
Revs/Mile
663.4

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