What Is Track Width Change?
Track width change, also called track change, is the difference in distance between the centerlines of the left and right wheels on the same axle after changing wheels, offset, or spacers.
A wheel that moves outward increases track width. A wheel that moves inward decreases it. The measurement is normally discussed for an axle, so changes on both sides are added together.
Track width is based on wheel centerlines, not the outer edges of the tires. It should not be confused with the change in the vehicle's overall tire width or fender-to-fender appearance.
How Offset and Spacers Change Track Width
Wheel offset determines where the wheel mounting face sits relative to the wheel's centerline:
- A lower positive offset moves the wheel outward.
- A higher positive offset moves the wheel inward.
- A spacer moves the wheel outward by the spacer's thickness.
For a like-for-like comparison on both sides of an axle, the basic calculation is:
Total track width change = 2 × outward movement per wheel
When comparing two wheel offsets without spacers:
Outward movement per wheel = original offset − new offset
For a spacer, the effective offset becomes:
Effective offset = wheel offset − spacer thickness
These calculations assume the offset values are measured in mm and that the same setup is used on both sides of the axle.
Examples
- Changing from ET45 wheels to ET35 wheels moves each wheel outward by 10 mm. The axle's total track width change is therefore 20 mm.
- Installing a 10 mm spacer behind an ET45 wheel produces an effective offset of approximately ET35. If spacers are fitted on both sides, the total track width increases by 20 mm.
- A 10 mm spacer on only one side changes that side's wheel position by 10 mm, but it does not create a symmetrical axle track change. Unequal side-to-side changes require particular caution.
If the new wheels have a different width, offset still determines the position of the wheel centerline. However, wheel width also changes how far the inner and outer rim edges extend. A track width calculation alone therefore does not describe all clearance changes.
Why Track Width Change Matters for Wheel Fitment
Changing track width can affect:
- Fender and outer-sidewall clearance
- Suspension and inner-wheel clearance
- Steering feel and scrub geometry
- The amount of wheel bearing leverage
- Alignment and tire wear if other geometry changes are introduced
- Whether the tire remains within applicable bodywork or inspection limits
A wider track does not automatically mean a wheel is compatible. Bolt pattern / PCD, center bore, wheel width, offset, brake clearance, lug hardware, suspension clearance, and tire size must still be checked separately.
For example, a normal spacer can increase track width and move a wheel outward, but it does not change the bolt pattern. A wheel with a different PCD may still be Not Directly Compatible unless a correctly designed bolt-pattern adapter is used.
Common Fitment Mistakes
Confusing per-wheel movement with total track change
A 10 mm outward movement on each side is a 20 mm increase across the axle, not a 10 mm increase. Always state whether a measurement applies per wheel or to the complete axle.
Treating offset as an isolated clearance measurement
Offset is referenced to the wheel centerline, so wheel width must be considered when checking the inner and outer edges. Two wheels with the same offset but different widths can have different clearance results.
Assuming a spacer only affects appearance
A spacer changes effective offset and track width, while also affecting the wheel mounting interface and available thread engagement. Spacer thickness, wheel seating, hub engagement, and lug hardware must be checked for the target vehicle.
Assuming more track is always better
Increasing track width may improve visual stance, but it can reduce fender clearance or create suspension contact. It may also alter steering and suspension loads. Track change is a geometry result, not a complete fitment approval.
What to Check Before Using Track Change in a Fitment Decision
- Record the original and new wheel offsets in mm.
- Account for any spacer thickness by calculating the effective offset.
- Calculate movement per wheel and total axle track change separately.
- Check wheel width and tire dimensions for inner and outer clearance.
- Verify bolt pattern / PCD, center bore, brake clearance, and lug hardware.
- Check the vehicle at full steering lock and through suspension travel.
Track width change is useful for predicting how a wheel setup alters vehicle geometry, but it should support–not replace–a complete wheel fitment check.