How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

0.33%

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

0.33%

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
8080.3+0.3
Tire 1Dia. 27.65 ″Rim 18 ″4.82 ″Width 9.65 ″Revs/Mile 729.5Circum. 86.9″Tire 2Dia. 27.74 ″Rim 18 ″4.87 ″Width 8.86 ″Revs/Mile 726.9Circum. 87.2″
Tire 1
Specification
Tire 2
27.65"
Diameter
27.74"
9.65"
Width
8.86"
4.82"
Sidewall
4.87"
86.851"
Circum.
87.161"
729.5
Revs/Mile
726.9

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