Michelin TRX
The Michelin TRX, (and the related TDX), is a radial tire introduced by the Michelin Group in 1975. It is one of the first volume-produced low-profile tires. Although technologically advanced, and reasonably successful, the tire's requirement for a non-standard rim ultimately condemned it to a relatively short commercial life. It has thus been called the "Betamax of the tire industry." Background and development. As passenger car performance increased during the 1970s, the need arose for improved tire capability. One of the possibilities was to reduce sidewall height, low sidewalls being common at the time  on crossply racing tires, but not usual for the better-performing radial tire. The problem was that reducing sidewall height compromised tire comfort, in part due to the roadwheel rim profile used. Michelin therefore decided to introduce the world's first tire and roadwheel system, where the two were designed together. This would enable both lower sidewall height, (for better roadholding) whilst retaining comfort due to better stress distribution within the tire, enabled by the redesigned wheel rim and tire bead. The "TR" was for "tension répartie", since tire stresses were better balanced in the new design, whilst the "X  was a reference to previous Michelin products such as the famous X" radial. TRX tires thus require the use of wheels that were specially designed for them; standard tires do not fit TRX wheels and vice versa. To avoid potentially dangerous confusion, Michelin used metric sizes for TRX roadwheels instead of the standard imperial wheel size (normally stated in inches). Usage. TRX tires were available either as standard or optional equipment on certain models of European makes such as BMW, Audi, Mercedes-Benz, Citroën, Peugeot, Ford, Ferrari, Alfa Romeo, Renault, and SAAB. They were also available on certain models of  the Ford Mustang, Ford Thunderbird, Mercury Capri, Mercury Cougar, and Mercury Lynx during the 1980s. Although most TRX tires were produced by Michelin, a few sizes were made by Avon, Continental, Goodyear (mainly for the American market) and Dunlop. Dunlop fitted their version of the TRX tire as standard equipment on Austin Montegos and Austin Mini Metros. TRX sizes. TRX wheels existed in diameters from to Some common TRX sizes and vehicles: <nowiki> Size Application </nowiki> Note: AV='front', AR='rear'. Does not include North American vehicles. Other sizes were available, for instance 160/65 R 315. Decline. Although  the tire gave good performance, and thus as noted above gained favour with some OEMs, its non-standard dimensions proved problematic in the aftermarket. It was also a notoriously hard tire to remove when using basic tools, a consequence of the deliberately designed strong fit between tire bead and rim. Rival manufacturers, such as Dunlop, thus produced replacement wheels and tires for popular cars, specifically for high-performance or winter conditions. In due course advances in tire technology caught up with the TRX line, enabling similar performance and greater convenience at lower cost. TRX tires are now produced only as  “young-timer” replacements for vehicles which were originally fitted with them. As of 2014, Michelin Classic was producing these tires in catalogue. References. Citations