How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

-1.68%

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

-1.68%

Absolute Difference

-0.49"

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
2019.7-0.3
3029.5-0.5
4039.3-0.7
5049.2-0.8
6059-1
7068.8-1.2
8078.7-1.3
Tire 1Dia. 29.10 ″Rim 18 ″5.55 ″Width 9.25 ″Revs/Mile 693.0Circum. 91.4″Tire 2Dia. 28.61 ″Rim 18 ″5.31 ″Width 9.65 ″Revs/Mile 704.9Circum. 89.9″
Tire 1
Specification
Tire 2
29.1"
Diameter
28.61"
9.25"
Width
9.65"
5.55"
Sidewall
5.31"
91.428"
Circum.
89.882"
693
Revs/Mile
704.9

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