How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

-1.08%

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

-1.08%

Absolute Difference

-0.3"

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
2019.8-0.2
3029.7-0.3
4039.6-0.4
5049.5-0.5
6059.4-0.6
7069.2-0.8
8079.1-0.9
Tire 1Dia. 27.70 ″Rim 15 ″6.35 ″Width 8.46 ″Revs/Mile 728.2Circum. 87.0″Tire 2Dia. 27.40 ″Rim 15 ″6.20 ″Width 8.86 ″Revs/Mile 736.0Circum. 86.1″
Tire 1
Specification
Tire 2
27.7"
Diameter
27.4"
8.46"
Width
8.86"
6.35"
Sidewall
6.2"
87.012"
Circum.
86.085"
728.2
Revs/Mile
736

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