How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

0.3%

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

0.3%

Absolute Difference

0.09"

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
2020.1+0.1
3030.1+0.1
4040.1+0.1
5050.2+0.2
6060.2+0.2
7070.2+0.2
8080.2+0.2
Tire 1Dia. 29.65 ″Rim 20 ″4.82 ″Width 9.65 ″Revs/Mile 680.3Circum. 93.1″Tire 2Dia. 29.74 ″Rim 20 ″4.87 ″Width 8.86 ″Revs/Mile 678.1Circum. 93.4″
Tire 1
Specification
Tire 2
29.65"
Diameter
29.74"
9.65"
Width
8.86"
4.82"
Sidewall
4.87"
93.135"
Circum.
93.444"
680.3
Revs/Mile
678.1

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