Target Wheel Position Calculator
Solve for the offset or spacer needed to place a wheel at a chosen position, such as flush with the fender. Inputs in mm or inches.
Solve for a desired static position.
Target Wheel Position Calculator: Tire Size Inputs
Compare two tire sizes here. Use the formulas and reference tables below for this tool's specific calculation.
How Target Wheel Position Calculator Works?
The Target Wheel Position Calculator works by converting a desired outward or inward movement into the required offset or spacer thickness. The tool uses 4 steps.
Measure the current position
Measure the inset from the fender lip to the tire or rim, for example 20 mm (0.79 in) inside.
Set the target
Type the target, for example 2 mm inside the fender lip, which needs 18 mm of outward movement.
Enter the current wheel
Type the current width and offset, for example 8.5 in ET40.
Read the solution
The calculator returns ET22 for a new wheel of the same width, or an 18 mm spacer for the current wheel.
Target Wheel Position Calculator Formula
The Target Wheel Position Calculator formula is ET_required = ET_current − Δ_target, where Δ_target is the outward movement wanted.
Δ = G_current − G_targetET_req = ET_cur − Δt = ΔET_req = ET_cur − Δ + (W_new − W_cur) × 12.7- G_current
- Current inset from fender (mm)
- G_target
- Target inset (mm)
- Δ
- Outward movement needed (mm)
Worked example
A 9.0 in ET35 wheel sits 27 mm (1.06 in) inside the fender. A target of 2 mm inside needs 25 mm of outward movement. The answer is ET10 on a new 9.0 in wheel or a 25 mm spacer. A 10.0 in wheel needs ET23 for the same outer position.
Target Wheel Position Calculator Conversion Table
The Target Wheel Position Calculator conversion table solves the required offset or spacer for 6 wheel position targets.
| Current wheel | Movement wanted | Required offset | Or spacer | New backspacing |
|---|---|---|---|---|
| 8.0" ET45 | +10 mm outward | ET35 | 10 mm spacer | 149.3 mm |
| 8.0" ET45 | +20 mm outward | ET25 | 20 mm spacer | 139.3 mm |
| 8.5" ET40 | +15 mm outward | ET25 | 15 mm spacer | 145.6 mm |
| 9.0" ET35 | +25 mm outward | ET10 | 25 mm spacer | 137.0 mm |
| 9.5" ET22 | +12 mm outward | ET10 | 12 mm spacer | 143.3 mm |
| 10.0" ET18 | +30 mm outward | ET-12 | 30 mm spacer | 127.7 mm |
What is Target Wheel Position Calculator?
A Target Wheel Position Calculator is a tool that works backward from a desired wheel position to the offset or spacer that achieves the position. Most fitment tools predict a position from a spec. The Target Wheel Position Calculator finds the spec from a position.
The calculator handles a change of wheel width. A wider wheel needs a higher offset to keep the same outer face position, by 12.7 mm (0.5 in) per added inch of width.
A real fitment target includes a margin for suspension travel, camber change and steering lock.
What are the uses of Target Wheel Position Calculator?
There are 4 main uses of the Target Wheel Position Calculator, including flush builds and custom wheel orders.
Flush builds
Find the exact ET for a flush fitment.
Custom wheel orders
Specify offset for a made-to-measure wheel.
Spacer sizing
Find the spacer thickness for a chosen look.
Width changes
Hold the outer position while changing wheel width.
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 changes toward suspension components.
Estimate tire movement toward the fender.
Estimate changes at the inner wheel edge.