Wintertime is roller training time: no airstream, but all the more sweat, stuffy indoor air and paralysing monotony. Can it get any worse? - some people think. Yes! The frame, clamped in the training roll, could break due to the different load; at least that is a fear that is circulating in road cycling circles and is also much discussed in the TOUR online forum.
So-called strain gauges are attached to this bike at neuralgic points, which can be used to measure and record how the frame deforms under load. As there was previously no reliable knowledge of the load on the roller, we did not look at the deformation of the clamped and therefore presumably most heavily loaded rear frame structure in isolation, but also recorded other parts of the frame. In order to be able to compare what happens to the frame, a fixed test programme with comparable pedalling frequencies was completed both on the roller and on the road. The range, controlled by means of a measuring crank, extended from basic training (100 watts) to sprint training (1,000 watts for a short time).
The bars show: In the three performance ranges analysed, the torsion of the down tube (TU), the bending of the right chain stay (BK) and the bending of the seat tube (BS) on the roller are usually lower than during comparable road training
The analysis of the data was surprising: with the same performance, the frame deforms more on the road than on the roller in almost all measurements. Only during sprinting, the maximum load for the material, did the frame deformation equalise between road and roller. As for the rider, the stress on the frame also increases from basic training to pedalling. If you look at the vibration amplitudes, you can see that the seat tube, chainstays and down tube are deformed the most. After analysing all the data, ADP engineer Peter Böhm concluded that the "corset roller trainer has a more supportive effect". Conversely, the "corset" is missing when riding on the road - the cyclist is more active, works more with the upper body and moves the bike more. For the same power output, this means that the forces acting on the frame via the handlebars, saddle and pedals are more varied. Added to this are the influences of the road surface. All these differences could explain the greater deformation measured compared to the roller.
Both curves show the lateral bending of the right-hand chainstay (BK) during the pedalling movement, once on the roller (yellow) and once on the road (grey). When the cyclist pedals (here at around 200 watts), the frame is deformed to varying degrees depending on the crank position. Clearly recognisable: The material stretches more when riding on the road than on the roller.
But where does the myth of frame-damaging roller training come from? One possible explanation could be the cyclist's "optical illusion": Under the weight of the (cradle) pedal stroke, the bottom bracket of the frame deflects just as far or even further to the side on the road as it does on the roller - only, due to the lack of a fixed reference point, the road cyclist doesn't notice this as much when looking from the saddle as he does in the room. Two things remain to be said. Firstly, no frame lasts forever - but if the tubular composite does break during training on the rollers, it will almost certainly be due to stresses that it has to endure on the road or has already endured in a long frame life. Secondly, our test only represents a small section of the world of roller training, so the results cannot be applied to every conceivable combination of roller trainer and frame. Too many influences play a role, such as the design, dimensions, history and material properties of the frame as well as the clamping. However, the fear that the bike could break during roller training is largely unfounded. The only remaining excuses for not training on a roller are the lack of airflow, stuffy indoor air and a certain monotony.
