Wheel Offset Calculator

Wheel-only bead-seat geometry

Compare wheel width and ET at the mounting face

Compare current and proposed rim width + signed ET. Results are nominal bead-seat edge changes, not tire sidewall or measured vehicle clearance.

What this calculator matches

Same ET concept, different calculation scope

Both tools show how a setup moves inboard or outboard. This page compares the wheel itself using declared bead-seat width and signed ET at one hub mounting face.

Calculated here

Nominal rim-edge position

Current and proposed declared wheel width
Signed ET and each bead-seat edge
Change on the suspension and fender sides

Not calculated here

Tire-envelope and spacer effects

Tire size, sidewall, diameter, or circumference
Wheel spacers or offset/backspacing conversion
Revs per mile, speedometer change, or measured clearance

Need tire diameter and circumference? Open the Tire Dimensions Calculator.

Where do they overlap? With the spacer set to none, changing ET by the same amount shifts a fixed rim or tire envelope by the same lateral amount. Do not compare these rim-edge results one-for-one when width, tire size, or spacer changes. A tire size such as 225/45R17 does not belong in these wheel-width fields.

Read the wheel before entering numbers

Offset is the gap between two reference planes

Keep the vehicle orientation fixed in every diagram: suspension is left, fender is right.

Find the two planesDeclared width uses the bead seats

Enter the width stamped on the wheel. Do not substitute the larger outside lip-to-lip measurement.

Read the ET signThe mounting face moves relative to centerline

A more positive ET generally places the rim farther inboard; a lower or negative ET places it farther outboard at the same hub.

Nominal rim-position change

Read each signed result with its direction

mm · up to 2 decimals

Nominal inner rim-clearance change

−2.7 mm2.7 mm less nominal clearance

Nominal outer rim-edge position change

+22.7 mm22.7 mm farther toward the fender

Result-driven geometry

Both rims share the same mounting-face zero

Scaled comparison

The rim spans are scaled only from the core-owned inner and outer extents. The dashed lines show each bead-seat centerline; the solid vertical line is the common hub mounting face.

Current · 7 in · ET +42

Inner extent: 130.9 mm
Outer extent: 46.9 mm

Proposed · 8 in · ET +32

Inner extent: 133.6 mm
Outer extent: 69.6 mm

Show formula steps and physical checks

Core calculation

Convert both declared bead-seat widths to millimeters without rounding.width mm = width in × 25.4, or entered millimeters
Locate the nominal inner and outer bead-seat edges from the hub mounting face.inner = width/2+ET; outer = width/2−ET
Subtract current positions from new positions using the displayed sign convention.edge movement = new extent−current extent; clearance change = −inner movement

Limits and checks

This is nominal bead-seat geometry, not a fitment verdict. Advertised wheel width commonly excludes flange thickness, and the mounted tire can extend beyond the wheel on both sides.
Positive inner-edge movement means closer to the suspension; positive inner-clearance change means more nominal clearance; positive outer-edge movement means farther toward the fender.
Physically verify the exact wheel and tire at full steering lock and throughout suspension travel. Separately confirm bolt pattern, centerbore, hub and brake clearance, load capacity, tire compatibility, fasteners, fender clearance, alignment, and vehicle/manufacturer requirements with a qualified installer.

Formula 1.0.0 · release execution

Declared rim position comparison

Translate wheel width and offset into nominal inner and outer movement

Wheel offset locates a rim's mounting face relative to its bead-seat centerline. This calculator compares two declared wheel widths and offsets to estimate rim-edge movement, while keeping actual tire, brake, suspension, hub, and body clearance outside the promise of the arithmetic.

Step-by-step guide · Declared rim position comparison

Resolve both extents with one sign convention

Inner extent: Half width + offset
Outer extent: Half width − offset
Width basis: Declared bead-seat width, not flange-to-flange

Normalize the current wheel
An 8-inch wheel has a declared width of 203.2 millimetres and a half width of 101.6 millimetres. At +35 millimetres offset, its nominal inner extent is 136.6 millimetres and its outer extent is 66.6 millimetres.
Normalize the proposed wheel
A 9-inch wheel is 228.6 millimetres wide with a half width of 114.3 millimetres. At +20 millimetres offset, its nominal inner extent is 134.3 millimetres and its outer extent is 94.3 millimetres.
Subtract current from proposed
The proposed inner edge movement is 134.3 − 136.6 = −2.3 millimetres. Its outer edge movement is 94.3 − 66.6 = +27.7 millimetres. Keeping the signed values prevents the two sides from being collapsed into an ambiguous statement such as 'moves out 30 millimetres.'
Translate edge movement into clearance language
Negative inner-edge movement means the nominal inner rim edge moves away from the suspension, so nominal inner clearance increases by 2.3 millimetres. Positive outer movement means the nominal outer rim edge moves toward the fender by 27.7 millimetres.

Translate wheel width and offset into nominal inner and outer movement: Calculate the current and proposed wheels independently before subtracting them. This makes every sign traceable to an actual edge position.

Offset begins at the bead-seat centerline

The input width is the wheel's declared bead-seat width. It is commonly stated in inches, whereas offset is commonly stated in millimetres. Convert width with the exact relationship 1 inch = 25.4 millimetres, divide by two to locate the bead-seat centerline, and then apply offset. The unit conversion calculator is useful for checking mixed-unit notes, but this worksheet performs the required inch-to-millimetre normalization itself.

In the calculator's declared sign convention, positive offset moves the mounting face toward the wheel's outboard side. Relative to that mounting face, nominal inner extent is half width plus offset and nominal outer extent is half width minus offset. A visual measurement across outer flange lips is normally wider than the declared bead-seat width and must not be substituted silently. ISO 3911 supplies wheel and rim vocabulary, while ISO 4000-2 addresses covered passenger-car rim designations and dimensions.

Resolve both extents with one sign convention

Calculate the current and proposed wheels independently before subtracting them. This makes every sign traceable to an actual edge position.

Normalize the current wheel
An 8-inch wheel has a declared width of 203.2 millimetres and a half width of 101.6 millimetres. At +35 millimetres offset, its nominal inner extent is 136.6 millimetres and its outer extent is 66.6 millimetres.
Normalize the proposed wheel
A 9-inch wheel is 228.6 millimetres wide with a half width of 114.3 millimetres. At +20 millimetres offset, its nominal inner extent is 134.3 millimetres and its outer extent is 94.3 millimetres.
Subtract current from proposed
The proposed inner edge movement is 134.3 − 136.6 = −2.3 millimetres. Its outer edge movement is 94.3 − 66.6 = +27.7 millimetres. Keeping the signed values prevents the two sides from being collapsed into an ambiguous statement such as 'moves out 30 millimetres.'
Translate edge movement into clearance language
Negative inner-edge movement means the nominal inner rim edge moves away from the suspension, so nominal inner clearance increases by 2.3 millimetres. Positive outer movement means the nominal outer rim edge moves toward the fender by 27.7 millimetres.

Read the signed outputs instead of memorizing a slogan

Inner edge movement

A positive value moves the nominal inner rim edge toward suspension-side components; a negative value moves it away. The calculator reports inner-clearance change with the opposite sign so that positive clearance change always means more nominal space.

Outer edge movement

A positive value moves the nominal outer rim edge toward the fender; a negative value tucks it inward. This describes the rim bead-seat geometry, not the tire's sidewall bulge or the fender clearance during cornering and suspension compression.

Relative width statistics

If a report needs the proposed width expressed as a percentage increase, the scientific calculator can provide that separate statistic. A percentage is not a substitute for signed millimetre movements, and neither number establishes safe physical clearance.

Nominal rim movement is not physical clearance

The formulas know only two widths and two offsets. They do not know spoke profile, brake-caliper envelope, hub face, center bore, adapters, spacers, studs, fasteners, suspension shape, alignment, steering angle, bodywork, axle load, or the path components follow through travel. Even a large calculated gap at one rim edge cannot rule out contact somewhere else. ISO 14400's safety and maintenance scope reinforces why a dimensional comparison cannot certify installation or continued service.

Tire shape is another independent layer. Nominal section width, approved rim-width range, construction, inflation, and load influence the mounted envelope. Use the tire dimensions calculator to decode theoretical passenger-tire diameter and circumference, not to infer the mounted section profile. Obtain manufacturer drawings or measured assemblies when the decision depends on a few millimetres.

Build a fitment record before mounting the wheel

Record the complete current and proposed wheel markings, including diameter, declared width, offset, contour, bolt pattern, center bore, load rating, and the exact part number. Confirm the inputs against manufacturer documentation rather than an advertisement alone.
Check vehicle-manufacturer permissions and obtain the required tire specification, mounting hardware, spacer or adapter policy, torque procedure, hub engagement, brake clearance, and dynamic clearance under steering, load, and full suspension travel.
Do not use offset arithmetic to predict engine speed or axle torque. Those are different mechanical questions; even the gear ratio calculator intentionally covers only one external spur-gear pair rather than an entire vehicle driveline.
Have a qualified professional inspect the proposed assembly and installation. Recheck fastening and contact according to applicable instructions, and stop using the setup if it rubs, loosens, leaks, vibrates, cracks, or produces abnormal handling or warning indications.

Important limitations

Wheel Offset Calculator is limited to the finite inputs, modes, and outputs stated for the Nominal wheel offset, inner clearance, and outer position comparison method. Check current declared wheel width, current width unit, current wheel offset (et), new declared wheel width, and new width unit, validation messages, the equation, and the stated display precision before relying on inner-edge movement (+ toward suspension), nominal inner-clearance change (+ more clearance), outer-edge movement (+ toward fender), and current declared width.

Review the stated scope, calculation method, assumptions, supported inputs, and effective dates, and obtain qualified advice before using a high-stakes result.

This formula passed its registered engineering tests and is published under an explicit site-owner policy authorization. No independent expert, QA, editorial, legal, or third-party review is claimed. Verify consequential results with a qualified professional.

Declared rim position comparison

Translate wheel width and offset into nominal inner and outer movement

Step-by-step guide · Declared rim position comparison

Resolve both extents with one sign convention

Inner extent: Half width + offset
Outer extent: Half width − offset
Width basis: Declared bead-seat width, not flange-to-flange

Normalize the current wheel
An 8-inch wheel has a declared width of 203.2 millimetres and a half width of 101.6 millimetres. At +35 millimetres offset, its nominal inner extent is 136.6 millimetres and its outer extent is 66.6 millimetres.
Normalize the proposed wheel
A 9-inch wheel is 228.6 millimetres wide with a half width of 114.3 millimetres. At +20 millimetres offset, its nominal inner extent is 134.3 millimetres and its outer extent is 94.3 millimetres.
Subtract current from proposed
The proposed inner edge movement is 134.3 − 136.6 = −2.3 millimetres. Its outer edge movement is 94.3 − 66.6 = +27.7 millimetres. Keeping the signed values prevents the two sides from being collapsed into an ambiguous statement such as 'moves out 30 millimetres.'
Translate edge movement into clearance language
Negative inner-edge movement means the nominal inner rim edge moves away from the suspension, so nominal inner clearance increases by 2.3 millimetres. Positive outer movement means the nominal outer rim edge moves toward the fender by 27.7 millimetres.

Offset begins at the bead-seat centerline

Resolve both extents with one sign convention

Calculate the current and proposed wheels independently before subtracting them. This makes every sign traceable to an actual edge position.

Normalize the current wheel
An 8-inch wheel has a declared width of 203.2 millimetres and a half width of 101.6 millimetres. At +35 millimetres offset, its nominal inner extent is 136.6 millimetres and its outer extent is 66.6 millimetres.
Normalize the proposed wheel
A 9-inch wheel is 228.6 millimetres wide with a half width of 114.3 millimetres. At +20 millimetres offset, its nominal inner extent is 134.3 millimetres and its outer extent is 94.3 millimetres.
Subtract current from proposed
The proposed inner edge movement is 134.3 − 136.6 = −2.3 millimetres. Its outer edge movement is 94.3 − 66.6 = +27.7 millimetres. Keeping the signed values prevents the two sides from being collapsed into an ambiguous statement such as 'moves out 30 millimetres.'
Translate edge movement into clearance language
Negative inner-edge movement means the nominal inner rim edge moves away from the suspension, so nominal inner clearance increases by 2.3 millimetres. Positive outer movement means the nominal outer rim edge moves toward the fender by 27.7 millimetres.

Read the signed outputs instead of memorizing a slogan

Inner edge movement

Outer edge movement

Relative width statistics

Nominal rim movement is not physical clearance

Build a fitment record before mounting the wheel

Record the complete current and proposed wheel markings, including diameter, declared width, offset, contour, bolt pattern, center bore, load rating, and the exact part number. Confirm the inputs against manufacturer documentation rather than an advertisement alone.
Check vehicle-manufacturer permissions and obtain the required tire specification, mounting hardware, spacer or adapter policy, torque procedure, hub engagement, brake clearance, and dynamic clearance under steering, load, and full suspension travel.
Do not use offset arithmetic to predict engine speed or axle torque. Those are different mechanical questions; even the gear ratio calculator intentionally covers only one external spur-gear pair rather than an entire vehicle driveline.
Have a qualified professional inspect the proposed assembly and installation. Recheck fastening and contact according to applicable instructions, and stop using the setup if it rubs, loosens, leaks, vibrates, cracks, or produces abnormal handling or warning indications.

Same ET concept, different calculation scope

Nominal rim-edge position

Tire-envelope and spacer effects

Offset is the gap between two reference planes

Enter both marked wheel specifications

Both rims share the same mounting-face zero

Current · 7 in · ET +42

Proposed · 8 in · ET +32

Core calculation

Limits and checks

Normalize the current wheel

Normalize the proposed wheel

Subtract current from proposed

Translate edge movement into clearance language

Offset begins at the bead-seat centerline

Resolve both extents with one sign convention

Read the signed outputs instead of memorizing a slogan

Inner edge movement

Outer edge movement

Relative width statistics

Nominal rim movement is not physical clearance

Build a fitment record before mounting the wheel

Important limitations

Same ET concept, different calculation scope

Nominal rim-edge position

Tire-envelope and spacer effects

Offset is the gap between two reference planes

Enter both marked wheel specifications

Both rims share the same mounting-face zero

Current · 7 in · ET +42

Proposed · 8 in · ET +32

Core calculation

Limits and checks

Normalize the current wheel

Normalize the proposed wheel

Subtract current from proposed

Translate edge movement into clearance language

Offset begins at the bead-seat centerline

Resolve both extents with one sign convention

Read the signed outputs instead of memorizing a slogan

Inner edge movement

Outer edge movement

Relative width statistics

Nominal rim movement is not physical clearance

Build a fitment record before mounting the wheel