Hybrid shifting on the TrueTrainer: what is it and how do we do it
Virtual shifting you know from our TrueBike uses a fixed gear and buttons to shift, while the TrueTrainer uses Hybrid Shifting, triggered by your road bike’s natural shifting. In this blog, we tell you what it is and how we do it.
Recap on Virtual Shifting
In our earlier blog, we explained Virtual Shifting. We explained that when you shift on your road bike, the speed of your bike does not change immediately but the speed of your crank does. On our TrueBike we can calculate how much we have to speed up or slow down your cranks, based on your previous gear choice and your new gear choice. We then feed the pedal forces you should experience into the robot and voila! You have shifted from one cog to another.
But what if you ride on a TrueTrainer and you still want to benefit from all our 400 gear sets? You don’t have electronic shifter buttons that allow you to shift virtually like on our TrueBike. But of course, you do have a cassette in the rear and in the front you have one, two or three gears. The front and rear gears normally dictate your gearing ratio and therefore the speed of your cranks for a given bike speed.
But that is where we switched things up: We don’t want you to be limited to the physical gears you have on your bike, we want you to choose any possible virtual gear set all with your current cassette and cogs. So now we only use your rear cassette and front rings as an indicator on which rear cog and front ring you have shifted. We then use the virtual gear set you selected to determine the speed of your cranks for a given virtual speed of your bike. And with that speed comes the force you should experience.
As you may have noticed, we have introduced the concept of virtual speed. On a normal bike trainer, the speed of rotation of your rear wheel dictates your road speed. And this road speed is part of the equations that govern how much you speed up or slow down given your pedal force and speed. However, if you have hybrid shifting the speed of the rear wheel is no longer tied to the speed in the model, your virtual speed.
How does hybrid shifting work?
So we know what, given the virtual speed of the bike, the speed of your crank should be. We now control the speed of your rear axle such that your cadence is correct. However, there is a slight rub: There is no constant relation between rear wheel speed and cadence since you have physical gear. In other words, depending on the cog on your rear cassette, your pedal speed will differ with the constant rotation of the trainer axle. But since we know which rear cog and front ring you are using, we can calculate what the rear axle speed should be for that your current physical gearing.
Physical gears no longer matter
It is now apparent that your physical gears no longer matter since the virtual gears dictate your cadence and the physical gears are only used for indexing. So what gears are best? Well quite simply put: any resistance unit, even our robot, benefits from speed. So you should use the gearing that helps you to get your rear axle to the highest speed. That is why we supply special cassettes with our virtual gears. They generate the highest speed. If you have a dedicated indoor bike, it even pays off to switch to large rings (53.39 for example) to make the speed of the rear axle higher. If you then want to ride a 50-34 compact, the virtual gears will solve that for you.
Hybrid shifting as a three-stage process:
Step 1: First our software detects which physical rear cog and front ring you are using.
Step 2: We figure out which virtual gears belong to the cog and ring and we calculate the cadence you need.
Step 3: Third we use the physical gearing of your cog and ring to adapt the axle speed so you feel the correct resistance.
There is one caveat: it takes a little while before we have measured your current gearing. Typically 3 to 5 pedal strokes and we need a minimum cadence of about 50 before we can start detecting. So after you changed your gearing it takes about 3 to 5 pedal strokes before we can start our three-step process to help you feel your new cadence. Until that point you will feel a change due to the physical gears changing, but not the possible added step of the impact of the virtual gears.