How the gears work

Virtual Gears was built and physically tested with a KICKR V5. Other direct-drive KICKR models are expected to work but have not yet been physically tested. It uses a Wahoo command that changes the trainer's idea of your wheel size: a smaller wheel covers less ground per pedal stroke, which feels like an easier gear. The riding app's own terrain command is left untouched, so the two never fight.

Virtual Gears chooses and displays the gear on the iPhone. The riding app sees an ordinary FTMS trainer and does not need a virtual-shifting feature of its own.

Opening Virtual Gears connects this transparent trainer proxy. Start Shifting adds the gears; Stop Shifting removes the virtual gear and restores the normal wheel circumference. Neither button starts or stops the ride in the riding app, and stopping shifting leaves that app connected.

The iPhone screen stays awake for as long as this trainer proxy is available. iOS changes Bluetooth advertising after the phone locks, which can make a waiting trainer disappear from riding apps on Windows and other computers.

Where the gears sit

Every gear is scaled away from the Normal wheel circumference in Settings, 2070 mm by default. The default ladder reaches about four times easier and 2.3 times harder while keeping gear 12 as the starting point. A drivetrain too wide to fit is refused at setup rather than mid-ride.

When the riding app has its own idea

Wheel size is part of the standard interface available to every riding app. Whenever one sets it, Virtual Gears honours it: that size becomes the new reference and every gear is rebuilt around it, so the gear you are in keeps feeling the way it did. Virtual Gears supports wheel sizes from 1800 mm to 2400 mm, which covers every real bicycle wheel; anything outside that is declined and the ride carries on at the size it already had.

If the riding app sends no size, the saved normal circumference is used. If it does send one, its value takes precedence and is restored when shifting stops.

Shifting waits for the trainer

Asking for a gear and getting it are not the same thing. Virtual Gears asks for the next gear only once the trainer has confirmed the last one, so holding a shift button sweeps through gears at whatever pace the trainer can really manage and stops the moment you let go. It cannot run ahead and hand you gears you did not ask for.

Measured on a Wahoo KICKR V5, a gear change is confirmed in 59 to 238 ms, averaging 138 ms.