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Automotive Calculator

Tire Size Source Comparison. Reconcile an original and vehicle-recommended candidate tire size from current placard, manual and exact-product records without treating nominal geometry as fitment approval.

Use this result well

Inputs that matter
One named tire-size source comparison and revision; exact vehicle year/make/model/trim/drivetrain/configuration; current placard, owner-manual or service-publication source; exact candidate-size recommendation; axle/position record and responsible reviewer; exact original and candidate tire product/specification sources; both nominal width/aspect/rim designations; an optional complete comparable pair of published revolutions per mile; optional indicated speed; and explicit vehicle-source, tire/wheel/load/speed, rolling/calibration and purchase/installation/driving boundaries
Output to expect
Original and candidate nominal unloaded sidewall, diameter and circumference; signed nominal diameter/radius differences; a clearly named ratio basis that prefers a complete pair of exact-product published rev/mi values and otherwise labels nominal unloaded diameter as fallback; an optional ratio-only speed illustration; complete vehicle/tire source evidence; deliberate page-session retention, copy/Markdown/print/share actions; and stable Project outputs that keep fitment, loaded circumference, calibration and every purchase/installation/service/driving approval false
How it works
Validate one coherent vehicle-recommended source record; reproduce nominal diameter as rim ×25.4 +2×width×aspect/100 for each label; compare candidate versus original nominal geometry without an acceptance threshold; when and only when both comparable exact-product rev/mi values are present, use original rev/mi ÷ candidate rev/mi for the optional speed ratio, otherwise use the explicitly labeled nominal-diameter fallback
  • The exact vehicle configuration, source revision, axle/position, candidate recommendation and both tire product/service-description records must travel together. One published rev/mi value cannot be mixed with nominal geometry, and another vehicle, trim, drivetrain, axle, wheel, tire product, pressure/load basis or source revision needs another record.
  • Arithmetic proximity is not fitment or safety approval. Keep approved rim range, wheel width/offset/load, load index/capacity, speed rating, construction, inflation, clearance, chains, TPMS, axle matching, driveline effects, loaded rolling circumference, speedometer/odometer calibration, purchase, installation, service, compliance and driving decisions with current vehicle/tire/wheel sources and qualified inspection.

Choose your path

Built around the job you need to finish

Reconcile one exact vehicle-recommended original/candidate tire-size pair from current vehicle and tire source records without turning nominal geometry or a speed ratio into fitment, calibration, installation or driving approval.

Owner checking a manufacturer-listed alternate size

Understand the documented arithmetic without relying on a generic percentage rule.

Identify the exact vehicle configuration, axle position, placard/manual row and written candidate recommendation; copy both nominal sizes and exact tire product sources; then reconcile the comparison.

Receives traceable nominal diameter/radius differences and can show which current vehicle source names the candidate without claiming the Tool approved fitment.

Service reviewer comparing exact product specifications

Avoid mixing one published rolling value with theoretical geometry from another product.

Enter a complete pair of comparable exact-product published revolutions-per-mile values or leave both blank, add an optional indicated speed and inspect the named ratio basis.

Can distinguish a paired source ratio from the nominal unloaded-diameter fallback and preserves product/revision identity with the result.

Phone-based buyer testing an unsupported candidate

Prevent a calculator from converting a close diameter into purchase or installation advice.

Load the static training record, trigger each vehicle/component/rolling/decision refusal, recover with documented boundaries, retain a snapshot, edit the live record and reset.

Unsupported paths focus the owning field and expose no stale result/action; retained evidence does not mutate and Reset clears both live and retained records.

Authoritative checks for this tool

Outputs and checklists are planning aids. Review the linked current authorities and the records, terms, instructions, and requirements that apply to your exact situation before a consequential decision.

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Reference & details

How it works

Source identity before arithmetic

Retain one exact vehicle configuration, placard or owner-manual row, axle position, written candidate recommendation, responsible reviewer and exact original/candidate tire product records. A percentage difference does not create a vehicle recommendation.

Nominal unloaded geometry

The size designation supplies nominal section width, aspect ratio and rim diameter. This arithmetic reproduces nominal sidewall, diameter and circumference; it does not measure a mounted, inflated and loaded tire.

Nominal diameter mm = rim inches × 25.4 + 2 × width mm × aspect / 100

Paired source ratio

When both exact tire sources publish revolutions per mile on a comparable basis, the Tool uses the pair for one speed-ratio illustration. If either value is absent, it labels nominal unloaded diameter as the fallback. Neither path certifies a vehicle speedometer or odometer.

Source ratio = original published rev/mi ÷ candidate published rev/mi

Updated: August 2026

Example Scenarios

Record the exact placard/manual/service source, axle position and written candidate row, then compare the two exact tire product sheets. The result is a traceable arithmetic record, not installation approval.

Leave both published-revolutions fields blank or obtain the missing comparable source. The Tool refuses to mix one loaded/source value with nominal geometry.

No comparison result is released as an approval. Return to the vehicle manufacturer, current owner/service material or a qualified tire professional for the responsible recommendation.

Common Mistakes to Avoid

Treating a small nominal percentage as approval

A close arithmetic result does not show that a vehicle manufacturer recommends the candidate or that the exact tire, wheel, load, speed, pressure and clearance requirements are satisfied.

Calculating absolute revolutions per mile from π × nominal diameter

Nominal diameter is unloaded label geometry. Use a complete pair of comparable exact-product published values when available and keep load, inflation, wear, deflection and slip outside the calculation.

FAQ

For this nominal geometry record, 225 is nominal section width in millimeters, 45 is nominal sidewall height as a percentage of section width, R denotes radial construction, and 17 is nominal rim diameter in inches. These fields do not identify a complete product, load/speed service description or vehicle approval.

No. It reports arithmetic differences and requires the exact candidate to be named by a current vehicle source. Vehicle, tire, wheel, axle, load, speed, pressure, clearance, TPMS and driveline requirements remain source- and configuration-specific.

No. It is one ratio illustration using either a complete pair of exact-product published revolutions-per-mile values or a clearly labeled nominal unloaded-diameter fallback. It does not model load, pressure, wear, deflection, slip, calibration logic or legal accuracy.

Two products with the same nominal size can have different specifications, service descriptions and published revolutions per mile. Keep product, size, load index/capacity, speed rating, revision and source row together.

No. Wheel width/offset/load, approved rim range, tire construction, inflation, suspension/brake/fender clearance, chains, TPMS, axle matching and driveline effects require current exact sources and qualified inspection.

About Tire Size Source Comparison

Compare one documented original/candidate pair only after identifying the exact vehicle configuration, axle position, current vehicle recommendation and both tire specification sources. The Tool reproduces nominal unloaded geometry and can compare a complete pair of published revolutions-per-mile values; it does not decide fitment, clearance, calibration or safe use.