How does a turbo trainer work?
The term "turbo trainer" is used mainly in the English-speaking world and includes all forms of trainers. Various trainers such as free roles, sometimes referred to as training rollers or simply rollers, fixed role trainers (with or without an online interface) or trainers with direct drive are combined in the global category "trainers". What they all have in common is that they are indoor sports equipment for cyclists to do realistic training with their bikes, preferably with their own bikes.
The basic principle is the same for all trainers: the movement of the bike on the trainer is being slowed down by various systems - this creates resistance that must be overcome by the athletic performance of the cyclist. The way in which the resistance is generated, whether this is done automatically or must be carried out manually by the athlete himself, the volume when generating the resistance and many other details vary greatly depending on the category and also the individual trainer.
Roller trainer or home trainer?
The main difference between a turbo trainer and a home trainer or a spinning bike is that the roller trainer uses its own bike as a sports device, which leads to a completely different driving experience (if only because of the position of the rider). The ability to shift different gears in response to the route profile further increases the level of realism and creates a "real driving experience".
The type of braking
As shown above, one of the main tasks of the trainer is braking: the changing resistance that arises on the road due to the surface and the incline or decline, but also the increasing air resistance due to the rise in speed should be simulated as realistically as possible. It can be said bluntly that the better the trainer, the more realistic the braking.
This means that with a simple trainer, the athletes themselves must regulate the resistance e.g. via a handlebar remote control, which then brakes the flywheel by means of a more or less complex and resilient construction. More modern and complex devices on the other hand have bidirectional, wireless interfaces by which a connected computer (notebook, tablet, smartphone) can give the trainer instructions on the braking power currently required. It is then possible to display a route on the screen (as a map, 3D or video) and to give the trainer the braking power according to the route and the speed traveled.
The differences between the categories of trainers and the individual devices are on one hand solely in the maximum braking force, which gives an indication of which degrees of incline can be realistically simulated. In addition to the pure power, there is also the speed of reaction to changing requirements in order to simulate short, crisp climbs or a workout. And last but not least, the accuracy of the implementation (usually specified in a percentage deviation) and compliance with the precision must also be observed.
A trainer who can simulate high gradients with brute force, but unfortunately only moves his brake magnets very slowly and thus only sluggishly reacts to changing requirements, is not really fun. Because in this case the ride experienced and the one displayed on the screen disharmonize very quickly. And if, in addition, the braking force cannot be kept constant, even though you are driving on a flat road or the workout actually specifies a constant value according to the video displayed, then the fun quickly is out of order and the trainer in question will quickly find itself in the corner collecting dust for a change.
High-precision devices, on the other hand, which, due to the lack of sufficient maximum braking force, have to switch over to a so-called virtual mode on every small incline (here an incline is simulated by extending the corresponding distance), are also no real fun. And since every resistance generated, no matter how generated, produces heat and that then has to be discharged from the housing in some form, both the cooling and the volume when braking also play a not only subordinate role.
Rollers or direct drive - the different designs
Roller trainers are available in a wide variety of designs: starting with free rolls (sometimes also referred to as free-running rolls) over to simple trainers in various designs all the way to trainers with direct drive.
The free roles represent the archetype of the trainer, in that the bike is relatively freely placed on 3 roles and simply suggests propulsion to the bike on the spot via the roles. The wheels are spinning and the connection of rear rollers with the roller for the front wheel generates gyroscopic forces that hold it upright. Free wheels have the most natural driving feel, but are not able to simulate high braking forces due to their principle (otherwise the gyroscopic forces would fail and the whole construction would become unstable).
The categories of fixed role and direct drive differ again to a great extent. With the fixed roller the rear wheel of the bicycle is placed on a small roller and the wheel is firmly clamped on the hub - hence the name "fixed roller". The firm clamping of the wheel and the weight of the athlete ensure on the one hand that the bicycle cannot tip over and on the other hand that the rear wheel sits on the roller just like on the road. When driving, the role gets braked in response to the simulated route or the executed training plan in order to generate the simulation. Fixed castors are usually simpler and therefore cheaper devices, but due to their design they can only simulate certain gradients as slip occurs at a certain force and the rear wheel simply slips through. In addition moving the wheel on the roll creates heat and abrasion - this also happens when driving on the road, but this construction does not move and is located in your own 4 walls. It's sometimes astonishing how much rubber abrasion can be found behind the trainer after a hard session - be commended if you don't have a white flokati.
Indoor or outdoor?
Due to the high mobility of a roller trainer, it can not only be used at home, but e.g. can also be taken to warm up for competitions. Most devices can be assembled and disassembled within a few minutes. For a long time, these devices have been used in racing by professional cyclists before / after the race in order to optimally warm up the muscles before the start. Or after an exertion such as in the case of track races (some of which are run in stages or laps) the lactate must be run out. But also in the hobby area such training devices are used more and more by athletes.