How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

1.84%

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

1.84%

Absolute Difference

0.56"

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
2020.4+0.4
3030.6+0.6
4040.7+0.7
5050.9+0.9
6061.1+1.1
7071.3+1.3
8081.5+1.5
Tire 1Dia. 30.50 ″Rim 17 ″6.75 ″Width 9.65 ″Revs/Mile 661.2Circum. 95.8″Tire 2Dia. 31.06 ″Rim 17 ″7.03 ″Width 10.04 ″Revs/Mile 649.4Circum. 97.6″
Tire 1
Specification
Tire 2
30.5"
Diameter
31.06"
9.65"
Width
10.04"
6.75"
Sidewall
7.03"
95.831"
Circum.
97.563"
661.2
Revs/Mile
649.4

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