How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

-1.63%

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

-1.63%

Absolute Difference

-0.49"

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
2019.7-0.3
3029.5-0.5
4039.3-0.7
5049.2-0.8
6059-1
7068.9-1.1
8078.7-1.3
Tire 1Dia. 30.10 ″Rim 20 ″5.05 ″Width 11.22 ″Revs/Mile 670.1Circum. 94.6″Tire 2Dia. 29.61 ″Rim 20 ″4.80 ″Width 12.01 ″Revs/Mile 681.2Circum. 93.0″
Tire 1
Specification
Tire 2
30.1"
Diameter
29.61"
11.22"
Width
12.01"
5.05"
Sidewall
4.8"
94.557"
Circum.
93.011"
670.1
Revs/Mile
681.2

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