How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

2.92%

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

2.92%

Absolute Difference

0.85"

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
2020.6+0.6
3030.9+0.9
4041.2+1.2
5051.5+1.5
6061.8+1.8
7072+2
8082.3+2.3
Tire 1Dia. 29.13 ″Rim 21 ″4.06 ″Width 11.61 ″Revs/Mile 692.4Circum. 91.5″Tire 2Dia. 29.98 ″Rim 21 ″4.49 ″Width 11.22 ″Revs/Mile 672.8Circum. 94.2″
Tire 1
Specification
Tire 2
29.13"
Diameter
29.98"
11.61"
Width
11.22"
4.06"
Sidewall
4.49"
91.514"
Circum.
94.174"
692.4
Revs/Mile
672.8

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