How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

-2.76%

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

-2.76%

Absolute Difference

-0.84"

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
3029.2-0.8
4038.9-1.1
5048.6-1.4
6058.3-1.7
7068.1-1.9
8077.8-2.2
Tire 1Dia. 30.45 ″Rim 20 ″5.23 ″Width 11.61 ″Revs/Mile 662.3Circum. 95.7″Tire 2Dia. 29.61 ″Rim 20 ″4.80 ″Width 12.01 ″Revs/Mile 681.2Circum. 93.0″
Tire 1
Specification
Tire 2
30.45"
Diameter
29.61"
11.61"
Width
12.01"
5.23"
Sidewall
4.8"
95.67"
Circum.
93.011"
662.3
Revs/Mile
681.2

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