In spring I purchased a real carbon frame gem. At present, however, I spend my time with it on the cycle trainer doing interval training, often out of the saddle. I’d like to know whether the bottom bracket can sustain damage when I ride out of the saddle, as the rear wheel is stiffly attached on the cycle trainer. It is clearly visible that the area around the bottom bracket and the chainstays gets twisted. Due to the fact that I’m not a lightweight (95 kg), I’m concerned that the frame might suffer from damage.
Reply by Dirk Zedler, TOUR technology expert and bicycle expert
Your question is justified. From bicycle manufacturers we’ve been hearing for a long time that the number of frame breakages and cracks increases after the winter period. This phenomenon was examined by TOUR a few years ago by measuring the loads on a cycle trainer with a real data bicycle and comparing them to the data measured on the road. The astonishing result: With identical riding manoeuvres the forces in the frame tubes are virtually the same as on the road. The visual impression that a bicycle on the cycle trainer is subject to increased bending results in particular from the fact that on the road you have no fixed point of reference to the movements of the frame and the parts – on the cycle trainer, however, you have. The technical difference lies in the fact that the rear wheel axle is firmly attached on the cycle trainer, as a consequence of which the rear wheel can not escape as it can on the road. The fixed drop-outs do not move or only a little, whereas the bottom bracket does. This leads to increased stress in the area of the drop-outs and the bottom bracket which may result in cracks over time. We therefore recommend not to mount high-value frames on the cycle trainer. Mount instead an older bicycle on the cycle trainer, another option is to buy a second-hand one for this purpose. In addition, the rollers of a cycle trainer are tyre killers, the premium material is much to precious.