How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

1.59%

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

1.59%

Absolute Difference

0.44"

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
2020.3+0.3
3030.5+0.5
4040.6+0.6
5050.8+0.8
6061+1
7071.1+1.1
8081.3+1.3
Tire 1Dia. 27.74 ″Rim 18 ″4.87 ″Width 8.86 ″Revs/Mile 726.9Circum. 87.2″Tire 2Dia. 28.18 ″Rim 18 ″5.09 ″Width 9.25 ″Revs/Mile 715.8Circum. 88.5″
Tire 1
Specification
Tire 2
27.74"
Diameter
28.18"
8.86"
Width
9.25"
4.87"
Sidewall
5.09"
87.161"
Circum.
88.521"
726.9
Revs/Mile
715.8

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