Virtual Shifting: How do you make an indoor bike shift realistically?

For the ultimate cycling experience on an indoor smart bike, cycling should feel as much as possible like outdoor cycling. An important part is that shifting gears on an indoor smart bike really should feel like you are on your road bike.

Because there are no real gears on an indoor smart bike, this is quite a challenge. Everything is done via one front sprocket and one rear sprocket. So how do you still simulate the feeling of real shifting? In this blog we explain how it works, why it is quite difficult and how TrueKinetix has tackled this.

Shifting gears on a road bike

For starters, let’s look at shifting gears on a road bike. When you shift gears the speed of your bike does not change, the ratio between your front and rear sprocket does change. This directly changes the speed of your crank and the resistance you experience on your pedals.


The moment you shift gears lighter on your road bike, the speed of your legs increases, because your legs have to follow the speed of your rear wheel with the new gearing. But because your legs move faster, you need to apply less force per pedal and the resistance is lower.
In summary: Shift down -> speed of your legs up -> less resistance on the pedals.

How do you give a realistic shifting feel on an indoor smart bike?

To match the outdoor shifting feel, your crank speed must change almost instantly from one speed to another. How fast? As fast as it takes to change the chain from one sprocket to another sprocket when cycling outdoors. That’s less than a second.

But how do you give the right crank speed on an indoor smart bike? When you shift gears, the cadence you need to experience changes, so we need to adjust the cadence and therefore the speed of the brake unit.  So, based on the bike speed you have and the gear you shifted, we know what your cadence should be. Since we know what the fixed ratio between your crank and your brake unit (a flywheel, or as in our case a robotized motor) is, we calculate what the speed of brake unit should be.

Why is realistic shifting with a flywheel difficult?

To simulate shifting, it is important to adjust the speed of the crank almost immediately. If you have a flywheel, this is practically impossible to do, because you then have to brake or accelerate that flywheel almost immediately, and a flywheel bike does not have the energy for that. As a result, shifting gears on a flywheel smartbike feels slower and thus less realistic. This is why flywheel bikes choose to use sound effects or vibrations to indicate shifting.

How does TrueKinetix simulate shifting?

As you now know, for a realistic shifting feel on an indoor smart bike, you must adjust the speed of the cranks almost immediately. Just as fast as it takes to shift the chain from one sprocket to another when cycling outdoors. How do we do it? We don’t use a flywheel as the braking unit, but a motor and robotics. This allows us to determine the speed of your cranks instantly and accurately. When you shift gears on a TrueBike, we instantly make your cranks move faster or slower by making the motor move faster or slower.

Determining the correct speed change is quite tricky. When we just started using this technique, the change in crank speed when shifting gears was so abrupt that it felt like a blow that made our test cyclists stop cycling in terror.

To make the shifting feel as realistic as possible, we created a mathematical model that determines exactly how fast the bike should slow down or accelerate to simulate shifting. This is exactly the reason why many customers report that they notice that shifting feels so fast and realistic on a TrueBike.