Knowledge base
Fitment Guides
Practical guides for tire sizing, wheel offset, pressure, load index and the math behind safe fitment.
Featured article · Calculator guides
How Speedometer Error Is Calculated
When you change tire size, your speedometer reading drifts. Here is exactly how the math works.
Tire size basics
Tire size basics
What Tire Size Difference Is Acceptable?
The 3% rule that pros use when plus-sizing or downsizing tires.
Tire size basics
Plus-Sizing Guide: How to Upgrade Wheel Size Safely
Plus-one and plus-two upgrades done right — keeping rolling diameter constant, picking the right tire width and offset, and knowing the comfort tradeoffs.
Tire size basics
What Is Wheel Offset (ET)? A Complete Engineering Guide
Offset, ET and Einpresstiefe explained from first principles — what positive, zero and negative offset mean for fitment, geometry and handling.
Tire size basics
Backspacing vs Offset: Conversion, Formula and When to Use Each
Backspacing and offset describe the same wheel from different reference points. Here is the exact conversion formula and when each measurement is used.
Tire size basics
Flush vs Aggressive Fitment: Stance, Poke and the Real-World Limits
Flush, aggressive, hellaflush and tucked — what these stance terms actually mean in offset numbers, and which combinations survive daily driving.
Tire size basics
How Wheel Offset Affects Handling, Scrub Radius and Bearing Life
Offset is not just visual. Here is exactly how moving the mounting face changes scrub radius, steering effort, bump-steer and the load on every hub bearing.
Tire size basics
Wheel Spacer Guide: Stance, Safety and the Math Behind ET Shift
What wheel spacers actually do, how the math relates to ET, and the thickness ranges that survive daily driving.
Tire size basics
Are Wheel Spacers Safe? Stud Engagement, Bearings and Real-World Limits
Spacers get a bad reputation, but the engineering is well-understood. Here is exactly when spacers are safe and when they become a hazard.
Tire size basics
Hub-Centric vs Universal Spacers: Why the Centering Interface Matters
Hub-centric and universal (lug-centric) spacers look similar but behave differently at speed. Here is what each does and which to buy.
Tire size basics
Spacer vs Lower-Offset Wheel: Which Is the Right Way to Get Flush?
Both achieve the same stance change on paper. Mechanically they are very different. Here is when to spacer existing wheels and when to buy lower-ET wheels.
Wheel fitment
Wheel fitment
Wheel Offset & Backspacing Explained
ET, offset, backspacing — the difference between a perfect fitment and rubbing.
Wheel fitment
Can Bigger Wheels Damage Your Suspension?
What plus-sizing does to ride quality, bearings, and bushings.
Wheel fitment
Wheel Offset vs Backspacing: What Is the Difference?
Two ways of describing the same wheel geometry. Here is how offset (ET) and backspacing relate, when each is used, and how to convert between them.
Safety & load
Safety & load
Tire Pressure Explained: PSI, Load and Tire Size Changes
What PSI really means, why the door placard matters more than any online calculator, and how a tire size change can shift the right pressure.
Safety & load
Tire Load Index Explained: How Much Weight Can a Tire Carry?
Decode the number after your tire size — what kg per tire it represents, how it relates to speed rating, and why you must never go below the OEM rating.