How It Works
How It Works
In this article we provide some background information to explain why using a turbo trainer feels so different to riding on the road, and explain how to set up your turbo trainer to give you the best experience and the most repeatable results if you are using Proxy Powertm, which also involves selecting the correct type of turbo in your Power+ profile. When I bought my first Turbo Trainer I didnâ€™t have much idea about setting it up. The first thing most people say about using a turbo is â€œwhy is it so much harder than riding on the road?â€ Hereâ€™s a bit of background to explain why that is. On a flat road you can freewheel and itâ€™ll take a while for the bike to stop. On a turbo if you stop pedalling the back wheel stops within a few seconds. So why is this? The answer is down to two words momentum and inertia. On the road you have the momentum of your weight and the weight of the bike to carry you forward. You might remember from maths or physics that momentum is calculated as weight multiplied by speed (velocity). On the turbo the only things that are moving are the back wheel (unless you have a direct drive turbo) and the revolving parts of the turbo itself e.g. the roller, the fan and the fly wheel. The weight of these parts and their momentum is much less than that of a bike and rider moving on the road. Consequently things stop moving sooner. If you look at a spin bike at a gym youâ€™ll see that it has a massive flywheel compared to the average turbo trainer. This gives a more realistic feel to the static bike. Inertia, in simple terms, is the desire of a mass (in this case you and your bike) to remain in its current state of movement unless acted upon by a force. So if you apply the brakes the bike will lose momentum, if you reach a hill and you donâ€™t apply more force to the pedals the bike will slow down due to the force of gravity. The faster you try to go the greater the air resistance, so you need more pedal force to go faster because the air resistance is a force trying to slow you down. So how does all this affect setting up the turbo? Turbo manufacturers do their best to produce trainers that will give cyclists a practical way to train without going out on the road, but they are limited by what they can produce by regulatory and market forces. Basically the turbo has got to be safe to use in the home and affordable. Commercially available turbo trainers (with one or two exceptions) tend to have small flywheels and so lack the capability to reproduce the momentum required to make it feel to the user like they are on the road. In terms of resistance (inertia) there are four ways this is provided: Using a fan which can be designed to mimic the air resistance created by a rider on the road. Using a fluid in a chamber that resists the movement of paddles on a spindle linked to the turbo roller or axle. Using magnetic force which can be varied by moving the magnets to simulate going up hill or into a head wind. Finally the moving parts of the turbo provide friction and a limited amount of inertia that resists accelerations. The main â€œmoving partâ€ for conventional turbo trainers is where the tyre meets the roller. The amount of pressure there is between the tyre and the roller greatly affects the amount of pedal force it takes to turn the back wheel. This is because at higher pressures the tyre will be deformed more, and it takes energy to deform the tyre. And this happens constantly and at high speed. Tyres can get very hot on the turbo. Special tyres are available for turbo training that help dissipate the heat generated by the friction. Direct drive turbo trainers avoid this problem by eliminating the tyre / roller interface, as they donâ€™t require a back wheel. But whichever combination of resistance is used, without a large flywheel to provide a simulation of rider momentum itâ€™s always going to feel different riding on a turbo to riding on the road. There isnâ€™t much momentum to carry the pedal stroke over the top-dead centre â€œdead spotâ€, so riding on a turbo usually feels like riding up hill. Riding up-hill you are going slower and battling against gravity as well as the other usual forces. Riding on the flat you going faster and the momentum carries the pedal stroke through the dead spot. So, when setting up the turbo for normal workouts you want to get to as near to â€œroad feelâ€ as you can. If you are using ProxyPowertm then you always want to set it up as near the same every time. The key variables are tyre pressure and roller pressure. If the turbo has variable resistance then you are likely to get the best â€œroad feelâ€ by setting it to the lowest resistance and using the gears to get the load you want by winding up the speed in the workout. The only time you wouldnâ€™t do this is if you wanted to do specific hill training on the turbo trainer and your range of gears didnâ€™t go high enough to generate that sort of resistance at your hill climb cadence. Itâ€™s not exact power, but given that the data were collected using a power meter itâ€™s usually within one or two percent. We havenâ€™t tested every type of turbo trainer in every resistance setting, so for those that we havenâ€™t tested we have used generic values. If you are using a turbo trainer that we havenâ€™t tested please set it up as described above using the manufactureâ€™s lowest resistance setting, and then use the gears to increase the effort required to drive the turbo, just like you would on a road ride. Starting from a â€œcold tyreâ€ i.e. one at room temperature, pump it up to about 80psi. It doesnâ€™t have to be exactly 80psi, but it does need to be the same pressure every time. Alternatively you can do your warm-up on the turbo, which will warm the tyre up, and then set the pressure before you start the workout itself. Either way, it needs to be the same pressure every time to take out the variability of random tyre pressure. Next you need to set the roller pressure. This needs to be just enough to avoid wheel slippage when you put the power down on the pedals, but no more than that. You donâ€™t want too much tyre deformation or the turbo trainer will feel like you are on a hill all the time. You need a round wheel for this to work (!) Even a slight â€œeggâ€ deformation in the rim, or in the way the tyre sits on the rim, will cause a variable pressure between the tyre and the roller. This will make the wheel slip in places because the pressure between the roller and the tyre will not be uniform. If you are using a Direct Drive turbo trainer then itâ€™s much simpler. The variables of tyre pressure, roller pressure and â€œout of trueâ€ wheels are eliminated making the resistance much more repeatable. The roll down test One way of checking that you have set the turbo up consistently is to do a roll down test. This is a pretty simple test to perform. You will need a timer. A mobile phone stop watch works well. Set the turbo trainer up as described above, get on the bike and pedal up to above 25mph / 40kph. Watch the speed. When the speed hits 25mph / 40kph start the stop watch. Stop the stop watch when the wheel stops rotating. That is the roll down time for your turbo with that wheel. Repeat the test when setting up the turbo next time. Roll down time is very dependent on the momentum in the turbo trainer, and we have already said that most donâ€™t have very much momentum. It is also dependent on the resistance setting of the turbo trainer, which should be the lowest setting for this test set up and general training. Finally, before using Power+ with your turbo, you should select the turbo manufacturer and type (including setting if the turbo is adjustable) from the dropdown options in your Power+ profile. This is vital if you donâ€™t have a Power Meter and you will be using ProxyPower.