Wheel Arch Gap Change Calculator
Estimate how the static gap between tire and wheel arch changes with a new tire size. Results in mm and inches from your measured gap.
Estimate static vertical gap changes.
Wheel Arch Gap Change Calculator: Tire Size Inputs
Compare two tire sizes here. Use the formulas and reference tables below for this tool's specific calculation.
How Wheel Arch Gap Change Calculator Works?
The Wheel Arch Gap Change Calculator works by subtracting the change in tire radius from the measured gap between the top of the tire and the fender arch. The tool uses 3 steps.
Measure the current gap
Measure straight up from the top of the tread to the arch lip with the vehicle on level ground, for example 40 mm (1.57 in).
Enter both sizes
Type the current and new tire sizes.
Read the new gap
The calculator subtracts half of the diameter gain from 40 mm and returns the new static gap.
Wheel Arch Gap Change Calculator Formula
The Wheel Arch Gap Change Calculator formula is Gap_new = Gap_measured − (OD_new − OD_old) ÷ 2.
Δr = (OD_new − OD_old) ÷ 2G_new = G_meas − ΔrΔG_in = −Δr ÷ 25.4- G_meas
- Measured gap at the top of the tire (mm)
- Δr
- Tire radius change (mm)
- G_new
- Predicted static gap (mm)
Worked example
A car with 225/45 R17 tires has a 40 mm (1.57 in) gap. A 245/40 R18 tire adds 9.5 mm of radius. The new static gap is 30.5 mm (1.20 in).
Wheel Arch Gap Change Calculator Conversion Table
The Wheel Arch Gap Change Calculator conversion table shows the new arch gap for 7 sizes from a 40 mm (1.57 in) measured baseline.
| New size | Radius change (mm) | Radius change (in) | New static gap |
|---|---|---|---|
| 225/40 R18 | +1.5 mm | +0.06 in | 38.5 mm (1.52 in) |
| 235/45 R17 | +4.5 mm | +0.18 in | 35.5 mm (1.40 in) |
| 245/40 R18 | +9.5 mm | +0.37 in | 30.5 mm (1.20 in) |
| 225/50 R17 | +11.2 mm | +0.44 in | 28.8 mm (1.13 in) |
| 235/40 R19 | +18.1 mm | +0.71 in | 21.9 mm (0.86 in) |
| 245/45 R18 | +21.7 mm | +0.85 in | 18.3 mm (0.72 in) |
| 215/45 R17 | -4.5 mm | -0.18 in | 44.5 mm (1.75 in) |
What is Wheel Arch Gap Change Calculator?
A Wheel Arch Gap Change Calculator is a tool that predicts the space left between the top of the tire and the fender after a tire size change. The tool works with a measured baseline, so the result fits the real vehicle and ride height.
The result is static. Suspension compression on bumps closes the gap by 50 to 100 mm (2 to 4 in) on most cars, so a small static gap often rubs in motion.
Lowered cars and stance builds use the tool to fill the arch without contact.
What are the uses of Wheel Arch Gap Change Calculator?
There are 4 main uses of the Wheel Arch Gap Change Calculator, including stance fitment and lowering spring planning.
Stance fitment
Fill the arch to a chosen gap with a taller tire.
Lowering spring planning
Check that lowering plus a tire change keeps a safe gap.
Rub prevention
Spot a gap too small for suspension travel.
Photo previews
Predict the visual gap before buying tires.
Related Clearance & Stance Tools
View All 134 Subtools →Estimate clearance changes from tire radius.
Compare manufacturer-specified loaded tire radii.
Estimate changes toward suspension components.
Estimate tire movement toward the fender.
Estimate changes at the inner wheel edge.
Estimate changes at the outer wheel edge.