How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

2.94%

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

2.94%

Absolute Difference

0.79"

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
2020.6+0.6
3030.9+0.9
4041.2+1.2
5051.5+1.5
6061.8+1.8
7072.1+2.1
8082.4+2.4
Tire 1Dia. 26.86 ″Rim 18 ″4.43 ″Width 8.86 ″Revs/Mile 750.9Circum. 84.4″Tire 2Dia. 27.65 ″Rim 18 ″4.82 ″Width 9.65 ″Revs/Mile 729.5Circum. 86.9″
Tire 1
Specification
Tire 2
26.86"
Diameter
27.65"
8.86"
Width
9.65"
4.43"
Sidewall
4.82"
84.378"
Circum.
86.851"
750.9
Revs/Mile
729.5

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