How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

1.29%

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

1.29%

Absolute Difference

0.37"

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
2020.3+0.3
3030.4+0.4
4040.5+0.5
5050.6+0.6
6060.8+0.8
7070.9+0.9
8081+1
Tire 1Dia. 28.63 ″Rim 18 ″5.31 ″Width 8.86 ″Revs/Mile 704.4Circum. 89.9″Tire 2Dia. 29.00 ″Rim 18 ″5.50 ″Width 8.46 ″Revs/Mile 695.4Circum. 91.1″
Tire 1
Specification
Tire 2
28.63"
Diameter
29"
8.86"
Width
8.46"
5.31"
Sidewall
5.5"
89.944"
Circum.
91.119"
704.4
Revs/Mile
695.4

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