How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

2.7%

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

2.7%

Absolute Difference

0.75"

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
2020.5+0.5
3030.8+0.8
4041.1+1.1
5051.4+1.4
6061.6+1.6
7071.9+1.9
8082.2+2.2
Tire 1Dia. 27.74 ″Rim 18 ″4.87 ″Width 8.86 ″Revs/Mile 726.9Circum. 87.2″Tire 2Dia. 28.49 ″Rim 18 ″5.25 ″Width 8.07 ″Revs/Mile 707.8Circum. 89.5″
Tire 1
Specification
Tire 2
27.74"
Diameter
28.49"
8.86"
Width
8.07"
4.87"
Sidewall
5.25"
87.161"
Circum.
89.511"
726.9
Revs/Mile
707.8

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