I have noticed on a very hot day in the south of France (it is over 40ºC today in the small town in the valley below my house which is up in the hills at 2500 feet altitude), I cannot quite use full throttle at the torque peak in second gear or I will get the very occasional belt skip, so I just avoid full throttle or change up early. The whole car has just been serviced by the excellent M3W Services, which included taking the whole back apart to fit a replacement fuel tank, so the belt must have been re-tensioned. I only notice this down at low altitudes on very hot days, so I am guessing that like almost all materials, the composite belt must expand with heat and maybe just enough to allow a skip at max torque. Now the belt is also in an area with not a lot of air flow and must be generating its own heat from hysteresis due to flexing. I wondered therefore if anyone had measured the belt temperature on a hot day. I would not be surprised if it was running at 20-30ºC above ambient. The pulleys will also be hot from friction and lubricant stirring in the bevel box plus braking heat transfer to the rear pulley from the rear brake drum. I assume the belt will be a superior material one made from SRS or similar type synthetic rubber on a kevlar/aramid core. I have not brought my IR remote thermometer with me to France or I would have measured the temperature today. If the belt is at say 70ºC, that is close to the operating limit for standard industrial toothed belt drives.
Wilson
