How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

-1.56%

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

-1.56%

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
2019.7-0.3
3029.5-0.5
4039.4-0.6
5049.2-0.8
6059.1-0.9
7068.9-1.1
8078.8-1.2
Tire 1Dia. 28.18 ″Rim 18 ″5.09 ″Width 9.25 ″Revs/Mile 715.8Circum. 88.5″Tire 2Dia. 27.74 ″Rim 18 ″4.87 ″Width 8.86 ″Revs/Mile 726.9Circum. 87.2″
Tire 1
Specification
Tire 2
28.18"
Diameter
27.74"
9.25"
Width
8.86"
5.09"
Sidewall
4.87"
88.521"
Circum.
87.161"
715.8
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