Track Width Change Calculator
Estimate axle track width change from offset changes, spacers and wheel swaps. Results per wheel and per axle in mm, inches and percent.
Estimate axle track changes.
Track Width Change Calculator: Tire Size Inputs
Compare two tire sizes here. Use the formulas and reference tables below for this tool's specific calculation.
How Track Width Change Calculator Works?
The Track Width Change Calculator works by doubling the per-wheel centerline shift, since both wheels on an axle move by the same amount. The tool uses 3 steps.
Enter the stock track
Type the published front or rear track width, for example 1,560 mm (61.4 in).
Enter offset or spacer changes
Type the offset change, the spacer thickness or both, for example ET45 to ET35.
Read the new track
The calculator returns a 20 mm (0.79 in) wider axle track, 1,580 mm, and a +1.28% change.
Track Width Change Calculator Formula
The Track Width Change Calculator formula is ΔTrack = 2 × ((ET_old − ET_new) + t_spacer).
Δc = (ET_old − ET_new) + t_sΔTrack = 2 × ΔcΔTrack ÷ Track × 100- Track
- Center-to-center tread distance across an axle (mm)
- t_s
- Spacer thickness (mm)
- Δc
- Centerline shift of one wheel (mm)
Worked example
A 1,560 mm (61.4 in) track with 15 mm spacers and a 10 mm lower offset widens by 2 × (10 + 15) = 50 mm (1.97 in). The new track is 1,610 mm (63.4 in), a 3.2% increase.
Track Width Change Calculator Conversion Table
The Track Width Change Calculator conversion table lists track change for 7 offset changes on a 1,560 mm (61.4 in) axle.
| Offset change | Centerline shift per wheel | Track change per axle | Percent change |
|---|---|---|---|
| -25 mm (ET change) | +25 mm | +50 mm (+1.97 in) | +3.21% |
| -15 mm (ET change) | +15 mm | +30 mm (+1.18 in) | +1.92% |
| -10 mm (ET change) | +10 mm | +20 mm (+0.79 in) | +1.28% |
| -5 mm (ET change) | +5 mm | +10 mm (+0.39 in) | +0.64% |
| +5 mm (ET change) | -5 mm | -10 mm (-0.39 in) | -0.64% |
| +10 mm (ET change) | -10 mm | -20 mm (-0.79 in) | -1.28% |
| +15 mm (ET change) | -15 mm | -30 mm (-1.18 in) | -1.92% |
What is Track Width Change Calculator?
A Track Width Change Calculator is a tool that estimates how much wider or narrower an axle becomes after a wheel or spacer change. Track width is measured between the centerlines of the 2 tires on one axle.
Wheel width alone does not change track width when the wheel's centerline stays put. Only offset and spacers move the centerline.
A wider track lowers weight transfer in corners and raises roll resistance. A change on one axle shifts handling balance.
What are the uses of Track Width Change Calculator?
There are 4 main uses of the Track Width Change Calculator, including handling tuning and class rule checks.
Handling tuning
Plan a wider front or rear track for balance.
Class rule checks
Stay inside the maximum track width of a racing class.
Width regulations
Check overall vehicle width against road rules.
Alignment records
Note track changes before an alignment.
Related Wheel Geometry & Fitment Tools
View All 134 Subtools →Calculate wheel mounting offset.
Compare old and new offsets.
Calculate backspacing using specified wheel dimensions.
Convert mounting measurements.
Calculate outward wheel projection.
Account for spacer thickness.