CheckFitment

By CheckFitment (Rainer Lang)

Overview

CheckFitment answers one question: will this wheel and tire fit your vehicle? Ask Claude for the bolt pattern of a 2019 Ford F-150 and the connector returns the bolt pattern in millimetres and inches, center bore, thread size, lug nut torque, OEM wheel sizes, offsets and tire sizes, each marked verified (two or more manufacturer sources) or unverified, with the sources listed. A vehicle that is not in the dataset is reported as not found; the connector never guesses. Five calculators use the same maths as checkfitment.com: compare an old and a new wheel (poke, inner clearance, backspacing) with or without tires; compare tire sizes (diameter change and speedometer error); size a wheel spacer and check stud engagement; work out the effective gear ratio after bigger tires and the ratio needed to restore it; and convert a bolt pattern between mm and inches with look-alike patterns that do not interchange. The connector is read-only and needs no account, no login and no API key. It receives only vehicle names and numbers, stores nothing and calls nothing outside the site. It shows no prices, no shop links and no affiliate links; every answer links to the matching free page on checkfitment.com. Results are planning estimates: confirm them against the vehicle's documentation and have fitment checked before you drive. Built and run by CheckFitment (Rainer Lang, Ellwangen, Germany). Not affiliated with any vehicle, wheel or tire maker, OpenAI or Anthropic.

Tools

bolt_pattern_facts

Claude

Use for "what is 5x114.3 in inches", "is 5x114.3 the same as 5x115", "will 6x135 wheels fit 6x139.7", or which vehicles use a pattern. Converts mm and inch notation, lists look-alike patterns that do not interchange, the vehicles in the dataset with that pattern, the lug tightening order and typical torque ranges by stud size (guidance only).

bolt_pattern_lookup

Claude

Use for "what is the bolt pattern on a 2019 Ford F-150", lug torque, center bore, thread size, OEM wheel size, offset or tire size of a vehicle, or "will these wheels fit my car" when the vehicle is named. Looks the vehicle up in the CheckFitment dataset (a fixed set of vehicles, each spec cited to manufacturer documents and marked verified or unverified). If the vehicle or year is not in the dataset the tool says so (not_in_database / year_covered false) and gives no figures; never fill them in from memory. Optional wheel_center_bore_mm runs the hub-centric check.

gear_ratio_calculator

Claude

Use for "what does my 3.73 axle behave like on 35s", "what ratio do I need to regear for 33s", RPM at highway speed after a tire change, or the crawl ratio (with transfer-case low ratio and first gear). Returns the effective ratio, RPM before and after in a 1:1 gear, the ratio that restores stock feel, the nearest gear set actually sold and how serious the change is.

tire_size_compare

Claude

Use for "what changes if I go from 265/70R17 to 285/75R17", "how far off is my speedometer with 33s", or odometer error after a tire change. Returns diameter, width, sidewall and ride-height change, the true speed when the speedometer shows a given value, the odometer error and how serious it is.

wheel_fitment_check

Claude

Use to compare a current wheel (and tire) with a new one: how far the outer edge pokes toward the fender and the inner edge toward the suspension, the diameter and ride-height change, speedometer effect, backspacing, and whether the new tire width suits the new rim width. With measured clearances (outer: tire edge to fender lip; inner: to the nearest suspension part, both on the current setup) it returns fits / tight / rub. Leave the tire fields out for a wheel-only offset comparison.

wheel_spacer_calculator

Claude

Use for "do I need spacers", "what spacer gets +35 wheels to +20", "is a 10 mm slip-on spacer safe". A spacer lowers the effective offset by its thickness. Returns the spacer needed for a target offset (and the nearest common size), the effective offset, track change, whether it is slip-on or bolt-on territory, and, with stud, stud_protrusion_mm and wheel_pad_thickness_mm, the slip-on thread-engagement check (≥ 1 × stud diameter and ≥ 6.5 turns).

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