Starlight Tools

Wheel Offset Calculator

Compare current and candidate wheel width, offset, and spacers to estimate changes in inner clearance, outer poke, and axle track. Add measured gaps for a static remaining-clearance estimate. Inputs stay in this browser tab.

Geometry comparison is not fitment approval The tool models nominal wheel position at the hub. It cannot see the tire sidewall, spokes, brake envelope, suspension travel, steering lock, bodywork, hub, fasteners, load rating, or vehicle-specific limits. Physically verify every candidate setup.

Compare two wheel setups

Current wheel

Width between bead seats.

Use a minus sign for negative offset.

Enter 0 when none is fitted.

Candidate wheel

Use the wheel's stated size.

Example: ET35 means +35 mm.

Spacer lowers effective offset.

Optional current measured gaps

Measure at the closest relevant point. Leave either field blank if unknown.

Closest wheel/tire-to-suspension gap.

Static outward room at the measured point.

Privacy: measurements are calculated locally. They are not uploaded, stored, or included in analytics events.

Wheel position comparison

Wheel offset, poke, and clearance formulas

Wheel offset is the signed distance from the hub mounting face to the rim centerline. Positive offset places the mounting face toward the wheel's outer face. A spacer moves the installed wheel outward, so this calculator first finds effective offset:

effective offset = marked offset − spacer thickness

Using labeled width converted to millimeters, nominal inboard and outboard positions are measured from the hub mounting face:

inboard position = width ÷ 2 + effective offset
outboard position = width ÷ 2 − effective offset

The comparison signs are chosen to be practical: positive inner-clearance change means more room, while positive outer-poke change means the candidate sits farther outward.

inner-clearance change = current inboard − candidate inboard
outer-poke change = candidate outboard − current outboard

About backspacing: labeled wheel width is measured between bead seats, while physical backspacing reaches the inner lip. The displayed backspacing uses the common approximation of adding 1 inch to labeled width before halving it. Flange design varies, so measure the actual wheel when backspacing precision matters.

How to compare wheel fitment safely

  1. Confirm the markings. Read width and offset from reliable wheel specifications or markings. Do not confuse wheel diameter, tire width, offset, and backspacing.
  2. Include installed spacers. Enter spacer thickness for each setup. A 5 mm spacer makes an ET45 wheel sit like ET40 for this position comparison.
  3. Measure the tightest gaps. If using measured clearances, check multiple points rather than one convenient location. The tire may be closer than the rim.
  4. Review both directions. A wheel can gain suspension clearance while losing fender room, or the reverse. Width and offset act together.
  5. Check dynamically. Verify brake and spoke clearance, hub seating, tire bulge, full steering lock, suspension compression and droop, loaded ride height, and body clearance.
  6. Confirm the complete specification. Bolt pattern, center bore, seat type, fastener engagement, load and pressure ratings, tire-to-rim approval, and applicable rules remain essential.

How to read positive and negative results

OutputPositive resultNegative result
Inner-clearance changeMore nominal room toward the suspensionLess nominal room toward the suspension
Outer-poke changeCandidate extends farther toward the fenderCandidate sits farther inward at the outer edge
Axle track changeWheel centerlines move farther apartWheel centerlines move closer together

The wheel-only edges are not the tire envelope. Tire section width, rim-width approval, sidewall shape, stretch or bulge, alignment, and deflection under load can change the closest point substantially.

Wheel offset calculator FAQs

Does a lower wheel offset create more poke?

With wheel width unchanged, a lower effective offset moves the wheel outward. That increases outer poke and axle track while creating more nominal room on the inboard side.

How is inner clearance change calculated?

Each wheel's nominal inboard position is half its labeled width plus effective offset. The calculator subtracts the candidate position from the current position, so a positive answer means more inner clearance and a negative answer means less.

How is outer poke change calculated?

Nominal outer position is half the labeled width minus effective offset. Candidate outer position minus current outer position gives the poke change, so a positive answer means the candidate projects farther outward.

How do wheel spacers affect offset?

A spacer moves the wheel outward. In this geometry model, effective offset equals marked offset minus spacer thickness. The calculator does not assess whether a spacer is approved or whether centering, hub engagement, fastener type and length, torque, or load effects are acceptable.

Is wheel offset the same as backspacing?

No. Offset is the distance from the mounting face to the rim centerline and is usually stated in millimeters. Backspacing runs from the mounting face to the inner wheel lip and is often measured in inches. Because labeled width excludes the outer flanges, conversion is approximate unless actual overall width is measured.

Does this wheel offset calculator guarantee fitment?

No. It compares static nominal wheel position. Tire shape, brake and spoke envelopes, suspension movement, steering lock, body clearance, hub bore, bolt pattern, fasteners, wheel strength, and legal requirements all need separate verification.

Are my wheel measurements tracked?

No. The calculation runs locally in your browser. This tool does not upload, store, or attach input values to analytics events.

Limits and safety disclaimer

  • Results use nominal labeled wheel width, not measured overall width. Rim flanges, tire sidewalls, weights, valve stems, spoke shapes, brake hardware, and manufacturing tolerances are not modeled.
  • Optional remaining-clearance values transfer a static measurement by the calculated wheel-edge change. They do not account for tire deformation, steering, alignment, heat, bearing movement, suspension travel, body roll, snow chains, or debris.
  • Track-width change describes wheel centerline movement from effective offset only. It does not predict scrub radius, bearing load, steering effort, handling, component life, alignment, or stability-control response.
  • Spacer use needs vehicle- and hardware-specific approval. Check hub-centric fit, wheel seating, fastener engagement, compatible nuts or bolts, torque procedure, and local law with qualified sources.

Safety disclaimer: This educational calculator is not a fitment approval, engineering assessment, inspection, or installation instruction. Use manufacturer-approved wheel and tire combinations or have the complete setup verified by a qualified wheel and tire professional.

Methodology and sources

Last reviewed: July 31, 2026. Offset terminology and fitment limits were checked against regulatory and industry material. The position equations follow directly from the offset definition and symmetric half-width geometry.

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