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Actual speed {{ resultsReady ? formatSpeed(computation.values.actual_speed) : '—' }} Ride height {{ resultsReady ? formatSignedLength(computation.values.ride_height_delta_mm) : '—' }} Width / side {{ resultsReady ? formatSignedLength(computation.values.per_side_width_delta_mm) : '—' }}
Examples: 225/55R17 or 31x10.50R15.
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The result is nominal; real mounted dimensions vary by tire model and rim width.
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Metric is the default; mph remains available for customary road-speed checks.
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Always confirm load index, speed rating, wheel width, offset, and vehicle guidance.
The neutral default is 0 and does not claim a clearance pass.
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This changes presentation only; the model continues to normalize geometry in millimeters.
MeasurementOriginalProposedChangeCopy
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Tire Replacement Cost Calculator Estimate installed tire replacement cost for one, two or four tires with tax and fees plus rebates, mileage value and shop-quote comparison.
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A replacement tire changes more than the gap around a wheel. Its overall diameter sets the distance travelled per revolution, so it affects indicated speed, recorded distance, effective gearing, and ride height. Its section width changes the space needed beside the strut, suspension, and bodywork. Those two dimensions can move in different directions.

Metric size codes mix three measurements. In 225/55R17, 225 is nominal section width in millimetres, 55 makes each sidewall 55% of that width, and 17 is wheel diameter in inches. Flotation notation such as 33x12.50R15 instead states an advertised overall diameter and width in inches, followed by the wheel diameter.

Sidewall height
The radial distance from the wheel edge to the nominal outer tread diameter.
Overall diameter
Wheel diameter plus two sidewalls, or the advertised flotation diameter.
Rolling circumference
The nominal distance covered by one revolution, calculated from overall diameter.
Per-side width change
Half the difference in section width, before wheel offset and rim effects are considered.

A taller tire travels farther per revolution. When a vehicle remains calibrated for the original circumference, actual road speed becomes higher than the speedometer reading and the odometer records fewer units than were travelled. A shorter tire reverses both effects.

Close diameter is useful for screening, but it is not fitment approval. Load index, speed rating, tire construction, wheel width, offset, brake clearance, steering sweep, suspension travel, tread depth, tire chains, and vehicle-specific guidance can reject a size that looks acceptable in nominal geometry. All-wheel-drive systems may also impose tighter matching requirements across all four tires.

Published sidewall dimensions are nominal. Mounted diameter and width vary with tire model, rim width, inflation pressure, load, wear, and manufacturing tolerance. Treat the comparison as a planning measurement, then verify the exact tire and vehicle.

How to Use This Tool:

Begin with the vehicle's current approved tire, then compare one proposed size under a screening band that matches the fitment risk.

  1. Enter the Original tire size and Proposed tire size in metric or flotation notation. Correct an unsupported range or incomplete code before using the comparison.
  2. Set a representative Speedometer reading and choose km/h or mph. This value scales the speed correction but does not affect tire geometry.
  3. Choose the Fitment screen: 2% for strict OEM or AWD-sensitive review, 3% for a daily replacement, or 5% for a lifted or custom setup. These are calculator screening bands, not manufacturer approvals.
  4. Enter measured clearance per side only when you have a useful physical measurement. Zero deliberately leaves clearance Not assessed.
  5. Review Geometry ledger for the dimensional changes and Fitment guidance for the band and clearance signals. Then confirm ratings, wheel compatibility, and vehicle guidance independently.

Interpreting Results:

Diameter change drives the selected 2%, 3%, or 5% screen. An absolute change at or below the chosen band is Within screen. A change above that band but no greater than 5% is Review; anything above 5% is Large change.

Actual speed estimates road speed while the speedometer still assumes the original tire. Odometer change moves in the opposite direction because fewer revolutions are counted with a taller tire. Neither value accounts for calibration changes made by the vehicle.

A clearance result considers only added nominal section width per side. Within measured gap does not check wheel offset, actual mounted width, diameter clearance, steering movement, or suspension compression. Physically inspect the full range of motion.

Technical Details:

Both supported notations are normalized to millimetres before comparison. The exact conversion 1 inch = 25.4 millimetres joins the inch wheel diameter to metric section width and keeps the downstream ratios unit-consistent.

Transformation Core

A metric code supplies width W, aspect ratio A, and wheel diameter R. A flotation code supplies advertised diameter, advertised width, and wheel diameter. Prefixes such as P, LT, ST, or T are accepted for metric codes but do not alter the geometry.

NotationSupported dimensional rangeNormalized quantities
MetricWidth 125–405 mm; aspect ratio 20–95; rim 10–26 inWidth, sidewall, rim, diameter, circumference
FlotationDiameter 20–44 in; width 5–16 in; rim 10–26 in; diameter must exceed rimAdvertised width and diameter converted to millimetres

Formula Core

For a metric size, sidewall height and nominal overall diameter are:

H=W×A100 D=(R×25.4)+2H

For flotation notation, advertised overall diameter is used directly and sidewall height is half the difference between that diameter and the wheel diameter. Circumference C, actual speed, and ride-height change follow:

C=πD vactual=vshown×CnewCoriginal Δride=Dnew−Doriginal2

Odometer change is (Coriginal / Cnew − 1) × 100%. Added width per side is the positive part of (Wnew − Woriginal) / 2.

Rule Core

The diameter screen owns its boundary: an absolute change equal to the selected band passes. The general review range ends at 5%, inclusive, and a value above 5% is always a large change. Clearance remains unassessed at exactly 0 mm; otherwise, added nominal width per side passes only when it is less than or equal to the entered clearance.

Worked Examples:

A plus-one wheel change

Changing from 225/55R17 to 245/50R18 raises nominal diameter from 679.3 mm to 702.2 mm, a 3.37% increase. At an indicated 100 km/h, the estimated actual speed is 103.37 km/h. The proposed tire is also 20 mm wider, or 10 mm per side, and raises nominal ride height by 11.45 mm. It sits outside the 3% daily screen, so fitment and calibration need review.

Safety and Accuracy Notes:

Use the vehicle owner's manual and tire-information label as the authority for replacement size, load capacity, and pressure. Have a qualified tire professional confirm the exact tire, wheel, offset, ratings, clearance, and drivetrain requirements before installation.

References: