How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

-1%

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%

Absolute Difference

-0.3"

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
2019.8-0.2
3029.7-0.3
4039.6-0.4
5049.5-0.5
6059.4-0.6
7069.3-0.7
8079.2-0.8
Tire 1Dia. 29.91 ″Rim 18 ″5.95 ″Width 10.83 ″Revs/Mile 674.3Circum. 94.0″Tire 2Dia. 29.61 ″Rim 18 ″5.81 ″Width 11.61 ″Revs/Mile 681.0Circum. 93.0″
Tire 1
Specification
Tire 2
29.91"
Diameter
29.61"
10.83"
Width
11.61"
5.95"
Sidewall
5.81"
93.963"
Circum.
93.036"
674.3
Revs/Mile
681

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