Publisher
SidewallRef is run by one independent developer, who also runs ThreadRef for screw threads, FittingKey for hydraulic and pneumatic fittings, MixRatio for concrete quantities and GaugePass for welding inspection. They are named here without links so the common ownership is plain. None of them covers tires.
Where the numbers come from
Dimensions such as section height, overall diameter and circumference are computed from the size code by the formulas the notation defines. The load index, speed symbol, UTQG and service type tables are transcribed from published sources, which the sources page lists along with any disagreements between them.
These are independent publishers, not independent measurements. Each one reproduces a table originally set by a standards body, so agreement between them shows a value was transcribed correctly, not that the underlying table is right. Where a figure is safety relevant, check it against the tire manufacturer's own data before relying on it.
Guides: credit and dates
The 6 guides cover what a size page cannot, such as what a sidewall marking is for or why a load index is not a licence. They appear under the SidewallRef name with no individual byline; their structured data names the SidewallRef organization as author, and no tire specialist or fitter is named anywhere. A guide's date changes when its wording does.
What the site will not tell you
This is geometry, not fitment approval. It says what a size measures, never whether it fits a vehicle.
SidewallRef calculates the dimensions a size code implies and reproduces the published load index and speed symbol tables. It does not know your vehicle.
Load index and speed rating must meet or exceed what the vehicle placard specifies. The placard is in the driver's door jamb on most vehicles and is the authority for your vehicle, not this site.
Clearance at full lock and full suspension travel, wheel width and offset, brake and suspension component clearance, axle load capacity, inflation pressure and any legal requirement where you drive are the owner's and the fitter's responsibility.
Nothing here approves a fitment. Confirm any change with a qualified tire fitter and with the vehicle manufacturer's own specification before driving on it.
Corrections
Found a size or table row that looks wrong? Send the row itself to [email protected]. The privacy page and the terms cover the rest.