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 sucessful, 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 togther. 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, Citroen, Peugeot, Ford, Ferrari, Alfa Romeo, Renault, and SAAB. They were also available on certain models of the Ford Mustang and Mercury Capri 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 possibly Dunlop.

Some common TRX sizes and vehicles

Size Application

• 170/65 R 365 TRX Citroën BX, Peugeot 305
• 185/65 HR 390 TRX SAAB 900 S and Turbo (1980/81)
• 190/65 HR 390 TRX Citroën CX, Ford Granada, Mercedes 200,220,240 Peugeot 504 Coupé, Renault 30TX
• 190/55 VR 340 TRX Alpine A310 V6 (AV), Renault 5 Turbo (AV), Alfa Sud Ti
• 220/55 VR 365 TRX Alpine A310 V6 (AR), R 5 Turbo (AR)
• 200/60 VR 390 TRX BMW 518, 520, 525, 528, 728, Mercedes 200, 220, 240, 300
• 210/55 VR 390 TRX CX 25 GTI Turbo
• 220/55 VR 390 TRX BMW 525, 528, 728, 535, 635 Csi, 735i, Ferrari 208, 308, Mondial 3,2 (AV)
• 240/55 VR 390 TRX Ferrari Mondial 8 & Cabriolet, Mondial 3,2 (AR)
• 240/55 VR 415 TRX Ferrari 400 Gti, 512 B, 412 Gti
• 240/45 ZR 415 TRX BMW 635 CSi, Ferrari 512 BB (AV), Testarossa (AV)
• 280/45 VR 415 TRX Ferrari 512 BB (AR), Testarossa (AR)

Note: AV='front', AR='rear'. Does not include North AMerican vehicles.

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 special-order replacements for vehicles which were originally fitted with them.

References

Citations

Notes

External links

• TRX page from Michelin Group website.
• Independant history and review of the TRX tire.
• Article on TRX tires for SAAB automobiles.