Inner Tire Clearance Change Calculator
Estimate how much closer a wider tire or new offset puts the inner sidewall to struts, springs and control arms. Results in mm and inches.
Estimate changes toward suspension components.
Inner Tire Clearance Change Calculator: Tire Size Inputs
Compare two tire sizes here. Use the formulas and reference tables below for this tool's specific calculation.
How Inner Tire Clearance Change Calculator Works?
The Inner Tire Clearance Change Calculator works by adding half of the tire width change to the change in wheel offset. The result is the movement of the inner sidewall toward the suspension. The tool uses 3 steps.
Measure the current gap
Measure from the inner sidewall to the nearest part, such as the strut, for example 15 mm (0.59 in).
Enter tire and offset changes
Type the old and new tire widths and wheel offsets (ET).
Read the remaining gap
The calculator subtracts the inward movement from 15 mm and flags any value under 5 mm (0.2 in).
Inner Tire Clearance Change Calculator Formula
The Inner Tire Clearance Change Calculator formula is Δinner = (W_new − W_old) ÷ 2 + (ET_new − ET_old), where a positive value moves the sidewall inward.
Δin = ΔW_tire ÷ 2 + ΔETG_new = G_meas − Δin- ΔW_tire
- Tire section width change (mm)
- ΔET
- Offset change (mm), higher ET moves the wheel inward
- G_meas
- Measured inner gap (mm)
Worked example
A tire 20 mm wider on a wheel with 10 mm more offset moves the inner sidewall 20 mm (0.79 in) inward. A 15 mm (0.59 in) gap becomes −5 mm, which means contact.
Inner Tire Clearance Change Calculator Conversion Table
The Inner Tire Clearance Change Calculator conversion table shows inner sidewall movement for 7 width and offset combinations from a 15 mm (0.59 in) measured gap.
| Tire width change | Offset change | Inward movement | Remaining gap |
|---|---|---|---|
| +10 mm (+0.39 in) | +0 mm | +5.0 mm (+0.20 in) | 10.0 mm |
| +20 mm (+0.79 in) | +0 mm | +10.0 mm (+0.39 in) | 5.0 mm |
| +20 mm (+0.79 in) | -10 mm | +0.0 mm (+0.00 in) | 15.0 mm |
| +20 mm (+0.79 in) | +10 mm | +20.0 mm (+0.79 in) | Contact (-5.0 mm) |
| +30 mm (+1.18 in) | +5 mm | +20.0 mm (+0.79 in) | Contact (-5.0 mm) |
| -10 mm (-0.39 in) | +0 mm | -5.0 mm (-0.20 in) | 20.0 mm |
| +40 mm (+1.57 in) | -15 mm | +5.0 mm (+0.20 in) | 10.0 mm |
What is Inner Tire Clearance Change Calculator?
An Inner Tire Clearance Change Calculator is a tool that predicts how far the inner sidewall of a tire moves toward the suspension after a width or offset change. MacPherson strut cars have the least inner room, often 10 to 20 mm (0.4 to 0.8 in).
Half of any width gain goes inward when the offset stays the same. A higher offset moves the whole wheel inward, and a lower offset moves the wheel outward.
Steering lock and suspension travel move the strut relative to the tire, so the static result needs a margin.
What are the uses of Inner Tire Clearance Change Calculator?
There are 4 main uses of the Inner Tire Clearance Change Calculator, including wider tire checks and offset selection.
Wider tire checks
Confirm a wider tire clears the strut or spring perch.
Offset selection
Pick an offset that keeps a safe inner gap.
Spacer sizing
Find the spacer needed to restore clearance.
Coilover fitment
Check clearance to coilover bodies and spring seats.
Related Clearance & Stance Tools
View All 134 Subtools →Estimate clearance changes from tire radius.
Compare manufacturer-specified loaded tire radii.
Estimate static vertical gap changes.
Estimate tire movement toward the fender.
Estimate changes at the inner wheel edge.
Estimate changes at the outer wheel edge.