How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

-1.81%

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

-1.81%

Absolute Difference

-0.57"

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
2019.6-0.4
3029.5-0.5
4039.3-0.7
5049.1-0.9
6058.9-1.1
7068.7-1.3
8078.6-1.4
Tire 1Dia. 31.56 ″Rim 18 ″6.78 ″Width 10.43 ″Revs/Mile 639.0Circum. 99.2″Tire 2Dia. 30.99 ″Rim 18 ″6.50 ″Width 10.83 ″Revs/Mile 650.7Circum. 97.4″
Tire 1
Specification
Tire 2
31.56"
Diameter
30.99"
10.43"
Width
10.83"
6.78"
Sidewall
6.5"
99.158"
Circum.
97.365"
639
Revs/Mile
650.7

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