How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

-2.86%

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

-2.86%

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
2019.4-0.6
3029.1-0.9
4038.9-1.1
5048.6-1.4
6058.3-1.7
7068-2
8077.7-2.3
Tire 1Dia. 27.65 ″Rim 18 ″4.82 ″Width 9.65 ″Revs/Mile 729.5Circum. 86.9″Tire 2Dia. 26.86 ″Rim 18 ″4.43 ″Width 8.86 ″Revs/Mile 750.9Circum. 84.4″
Tire 1
Specification
Tire 2
27.65"
Diameter
26.86"
9.65"
Width
8.86"
4.82"
Sidewall
4.43"
86.851"
Circum.
84.378"
729.5
Revs/Mile
750.9

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