Tire size & wheel offset calculator
Find equivalent tire sizes for different rim diameters
Compare two tire sizes side by side
| Metric | Size 1 | Size 2 | Difference |
|---|
When speedometer shows these speeds with Size 1, actual speed with Size 2:
| 20 | 30 | 40 | 50 | 60 | 70 | 80 | 90 | |
|---|---|---|---|---|---|---|---|---|
| Reading | 20 | 30 | 40 | 50 | 60 | 70 | 80 | 90 |
| Actual | 20.2 | 30.3 | 40.4 | 50.5 | 60.6 | 70.7 | 80.8 | 90.9 |
Calculate offset changes when swapping wheels or adding spacers
New setup will sit 12mm further out
Width change: +0.5" width = ~6.35mm wider per side
Spacer effect: Pushes wheel out by spacer size
Lower offset: Wheel sits further out (more poke)
Higher offset: Wheel tucks in more
Find equivalent tire sizes when upgrading or downgrading wheel diameter
Plus 1 (+1): Go up 1" in rim diameter, reduce aspect ratio
Plus 2 (+2): Go up 2" in rim diameter, reduce aspect ratio more
Minus 1 (-1): Go down 1" in rim diameter, increase aspect ratio
Goal: Maintain overall tire diameter for accurate speedometer
Calculate fitment for different front and rear wheel/tire configurations
Common on: RWD sports cars (BMW M, Mercedes AMG, Mustang, etc.)
Purpose: Wider rear tires for better traction and aggressive stance
Rotation: Cannot rotate tires front-to-rear with staggered setup
Tip: Try to keep front/rear diameters within 1% for minimal speedo error
Find OEM wheel and tire specs for your vehicle
See what wheels and tires others are running on their vehicles
Select a vehicle above to view OEM specs and community setups