How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

1.18%

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

1.18%

Absolute Difference

0.36"

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
2020.2+0.2
3030.4+0.4
4040.5+0.5
5050.6+0.6
6060.7+0.7
7070.8+0.8
8080.9+0.9
Tire 1Dia. 30.45 ″Rim 20 ″5.23 ″Width 11.61 ″Revs/Mile 662.3Circum. 95.7″Tire 2Dia. 30.81 ″Rim 20 ″5.40 ″Width 12.01 ″Revs/Mile 654.7Circum. 96.8″
Tire 1
Specification
Tire 2
30.45"
Diameter
30.81"
11.61"
Width
12.01"
5.23"
Sidewall
5.4"
95.67"
Circum.
96.783"
662.3
Revs/Mile
654.7

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