{"openapi":"3.1.0","info":{"title":"Tire Size API","version":"1.0.0","description":"Tyre-size geometry as an API, computed locally and deterministically. The dimensions endpoint parses a metric tyre code such as 205/55R16 — or separate width, aspect ratio and rim values — into its full geometry: the sidewall height (width·aspect/100), the overall diameter (rim·25.4 + 2·sidewall) in millimetres and inches, the rolling circumference, and the revolutions per kilometre and per mile; a 205/55R16 works out to a 112.75 mm sidewall and a 631.9 mm (24.88 in) outside diameter. The compare endpoint takes an original and a replacement size and computes the speedometer error and ground-clearance change of swapping between them: because the speedometer is calibrated to the original rolling diameter, a larger tyre makes it read low, so true speed = indicated · OD_new/OD_old, and a tyre that is 2 % bigger means an indicated 100 is really about 102 km/h. Staying within ±3 % keeps the error and clearance change small. Tyre codes use the metric P-metric/Euro-metric form. Everything is computed locally and deterministically, so it is instant and private. Ideal for automotive, tyre-shop, fitment, car-enthusiast, fleet and vehicle-spec app developers, plus-sizing and speedo-error tools, and garage software. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 2 endpoints. This is metric tyre geometry; for fuel economy use a fuel-economy API.","contact":{"name":"PremiumApi","url":"https://www.oanor.com/by/premiumapi"}},"servers":[{"url":"https://api.oanor.com/tiresize-api","description":"oanor gateway"}],"tags":[{"name":"TireSize"},{"name":"Meta"}],"components":{"securitySchemes":{"oanorKey":{"type":"apiKey","in":"header","name":"x-oanor-key","description":"Get your key at https://www.oanor.com/developer/keys"}}},"security":[{"oanorKey":[]}],"paths":{"/v1/compare":{"get":{"operationId":"get_v1_compare","tags":["TireSize"],"summary":"Speedometer error between sizes","description":"","parameters":[{"name":"original_size","in":"query","required":true,"description":"Original tyre (e.g. 205/55R16)","schema":{"type":"string"},"example":"205/55R16"},{"name":"new_size","in":"query","required":true,"description":"New tyre (e.g. 225/45R17)","schema":{"type":"string"},"example":"225/45R17"}],"security":[{"oanorKey":[]}],"responses":{"200":{"description":"OK","content":{"application/json":{"example":{"data":{"note":"Speedometer is calibrated to the original rolling diameter. A larger new tyre makes the speedo read low: true speed = indicated · OD_new/OD_old. Stay within ±3 % to keep the error small.","inputs":{"original":"205/55R16","replacement":"225/45R17"},"speedometer":{"reads":"slow (you are going faster than shown)","true_speed_at_indicated_100":100.3798},"new_diameter_mm":634.3,"original_diameter_mm":631.9,"diameter_difference_mm":2.4,"ground_clearance_change_mm":1.2,"diameter_difference_percent":0.3798},"meta":{"timestamp":"2026-06-05T19:50:20.881Z","request_id":"5222a9cb-e8cd-496b-9295-74268ea4de78"},"status":"ok","message":"Tyre comparison / speedo error","success":true}}}},"401":{"description":"Missing or invalid x-oanor-key header"},"402":{"description":"Active subscription required"},"429":{"description":"Rate-limit or monthly quota reached"},"502":{"description":"Upstream did not respond"}}}},"/v1/dimensions":{"get":{"operationId":"get_v1_dimensions","tags":["TireSize"],"summary":"Tyre geometry from a size","description":"","parameters":[{"name":"size","in":"query","required":false,"description":"Tyre code (e.g. 205/55R16)","schema":{"type":"string"},"example":"205/55R16"},{"name":"width","in":"query","required":false,"description":"Or section width (mm)","schema":{"type":"string"}},{"name":"aspect","in":"query","required":false,"description":"Aspect ratio (%)","schema":{"type":"string"}},{"name":"rim","in":"query","required":false,"description":"Rim diameter (in)","schema":{"type":"string"}}],"security":[{"oanorKey":[]}],"responses":{"200":{"description":"OK","content":{"application/json":{"example":{"data":{"note":"Sidewall = width·aspect/100 (mm); overall diameter = rim·25.4 + 2·sidewall. 205/55R16 ≈ 631.9 mm (24.88 in) outside diameter.","inputs":{"size":"205/55R16"},"revs_per_km":503.7346,"aspect_ratio":55,"revs_per_mile":810.6822,"circumference_m":1.985172,"rim_diameter_in":16,"circumference_mm":1985.1724,"section_width_mm":205,"sidewall_height_mm":112.75,"overall_diameter_in":24.87795,"overall_diameter_mm":631.9},"meta":{"timestamp":"2026-06-05T19:50:20.979Z","request_id":"008af342-fa7d-412f-8501-428bfef7463e"},"status":"ok","message":"Tyre dimensions","success":true}}}},"401":{"description":"Missing or invalid x-oanor-key header"},"402":{"description":"Active subscription required"},"429":{"description":"Rate-limit or monthly quota reached"},"502":{"description":"Upstream did not respond"}}}},"/v1/meta":{"get":{"operationId":"get_v1_meta","tags":["Meta"],"summary":"Spec","description":"","parameters":[],"security":[{"oanorKey":[]}],"responses":{"200":{"description":"OK","content":{"application/json":{"example":{"data":{"notes":"Tyre codes like 205/55R16, or width (mm) + aspect (%) + rim (in). Section width and sidewall in mm, rim and diameters also in inches. Geometry only — actual rolling radius is a little smaller under load.","service":"tiresize-api","endpoints":{"GET /v1/meta":"This document.","GET /v1/compare":"Speedometer error and clearance change between two tyre sizes.","GET /v1/dimensions":"Parse a tyre size (e.g. 205/55R16) into its full geometry."},"description":"Tyre size geometry: overall diameter, circumference and revolutions from a tyre code, and speedometer error when changing size."},"meta":{"timestamp":"2026-06-05T19:50:21.095Z","request_id":"ba2cc2d6-1b69-482a-8dd3-d1bc9825c2f0"},"status":"ok","message":"Meta","success":true}}}},"401":{"description":"Missing or invalid x-oanor-key header"},"402":{"description":"Active subscription required"},"429":{"description":"Rate-limit or monthly quota reached"},"502":{"description":"Upstream did not respond"}}}}},"x-oanor-pricing":[{"slug":"free","name":"Free","price_cents_month":0,"monthly_call_quota":7200,"rps_limit":2,"hard_limit":true},{"slug":"starter","name":"Starter","price_cents_month":470,"monthly_call_quota":72000,"rps_limit":6,"hard_limit":true},{"slug":"pro","name":"Pro","price_cents_month":1280,"monthly_call_quota":320000,"rps_limit":15,"hard_limit":true},{"slug":"mega","name":"Mega","price_cents_month":4000,"monthly_call_quota":1700000,"rps_limit":40,"hard_limit":true}],"x-oanor-marketplace-url":"https://www.oanor.com/api/tiresize-api"}