Until the TRX, low profile meant a sidewall height that was typically seventy per cent of the width of the tyre. The TRX tyre is one half of a system that combines the road wheel with the tyre to spread the stresses created in a much lower-profile tyre designed for high speed work. The TR stands for Tension Repartie or distributed tension. The TRX, which runs in profiles all the way down to 45, uses a metric system of measurement. This means it can't be confused with regular tyres that won't fit these rims, although the system itself often causes confusion. Here's a quick primer: the 190/55VR340 has a 190mm section width (191mm, actually, but this would look clumsy on the sidewall), the profile is 55, meaning the sidewall height is 55 per cent of the width. The V is the speed rating (149mph max) and the ‘R’ stands for radial. Finally, 340 denotes the rim diameter in mm.

The TRX GT was the final development of the TRX concept. Released in 1982 it was developed with BMW for its 635 CSi coupe, and has a completely different tread pattern to the earlier TRX.

This 240/45VR415 fits: BMW 635 CSi and M635Csi, Ferrari 512BB and Testarossa (front tyre).

High-performance metric radial tubeless tyre.