How it works

TireFlows

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

Tire 1
/R
Tire 2
/R

Result

Diameter Difference

2.58%

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

2.58%

Absolute Difference

0.75"

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
2020.5+0.5
3030.8+0.8
4041+1
5051.3+1.3
6061.5+1.5
7071.8+1.8
8082.1+2.1
Tire 1Dia. 29.10 ″Rim 18 ″5.55 ″Width 9.25 ″Revs/Mile 693.0Circum. 91.4″Tire 2Dia. 29.85 ″Rim 18 ″5.93 ″Width 8.46 ″Revs/Mile 675.6Circum. 93.8″
Tire 1
Specification
Tire 2
29.1"
Diameter
29.85"
9.25"
Width
8.46"
5.55"
Sidewall
5.93"
91.428"
Circum.
93.778"
693
Revs/Mile
675.6

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