How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

-1.19%

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

-1.19%

Absolute Difference

-0.35"

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
3029.6-0.4
4039.5-0.5
5049.4-0.6
6059.3-0.7
7069.2-0.8
8079-1
Tire 1Dia. 29.39 ″Rim 20 ″4.69 ″Width 10.43 ″Revs/Mile 686.2Circum. 92.3″Tire 2Dia. 29.04 ″Rim 20 ″4.52 ″Width 10.04 ″Revs/Mile 694.6Circum. 91.2″
Tire 1
Specification
Tire 2
29.39"
Diameter
29.04"
10.43"
Width
10.04"
4.69"
Sidewall
4.52"
92.331"
Circum.
91.218"
686.2
Revs/Mile
694.6

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