How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

1.64%

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

1.64%

Absolute Difference

0.47"

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
3030.5+0.5
4040.7+0.7
5050.8+0.8
6061+1
7071.1+1.1
8081.3+1.3
Tire 1Dia. 28.63 ″Rim 18 ″5.31 ″Width 8.86 ″Revs/Mile 704.4Circum. 89.9″Tire 2Dia. 29.10 ″Rim 18 ″5.55 ″Width 9.25 ″Revs/Mile 693.0Circum. 91.4″
Tire 1
Specification
Tire 2
28.63"
Diameter
29.1"
8.86"
Width
9.25"
5.31"
Sidewall
5.55"
89.944"
Circum.
91.428"
704.4
Revs/Mile
693

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