Caddence, speed and physics

I know this is still moving forward, but not sure what is going on. Is there a cadence threshold in order to get moving or stopping? If I stop pedaling, and put on the brakes on a flat section, the bike keeps going. I fi stop pedaling on an uphill it stop immediately. It also takes a second or two to get going again.

Cadence seems to be the driving force behind movement too, am I correct in saying that? I removed the speed sensor magnet and spun the wheel without turning the cranks and no movement on the screen.

Last thing is the loss of speed going down a 5.3% grade decent, not realistic a all. It seems as if you are headed down a slope and you encounter just a slight ascent, you lose 8-10mph after hitting 40+.

Zwift is awesome, just a few more things to look at amongst the million others.

Cadence…stupid keyboard has a run away d!

Hi David,

Power and speed are the main forces at play in Zwift. Power is what Zwift uses to calculate your on-screen avatar’s speed. A speed sensor is necessary when using zPower as Zwift calculates your wattage output based on the turbo trainer used and the speed your back wheel is spinning.

Cadence is there for your own training purposes and to help animate your avatar in a more correct fashion.

so why is it that I can spin the rear wheel with the speed sensor and there is no movement on the screen until I turn the cranks with the cadence sensor? 

Hi David,

You can spin that wheel freely and it should move the rider - the speed sensor data is the only data we’re looking at. We’ve been testing Zwift on zPower with only a speed sensor and no cadence sensor for simplicity’s sake (and to not have to constantly pair 2 items).

I find this strange as well. I have a Wahoo Kickr. You should be able to measure speed and power from the Kickr directly. The power seems somewhat accurate, but I can be in my 52,11 spining a 110 cadence and Zwift reads 26 mph on some points on the map. That’s totally inaccurate. I’m still trying to figure this one out.



Zwift reads the wattage directly from your KICKR and uses that to determine speed based on virtual things like wind resistance and elevation.

Nope, I get nothing until the crank hits the cadence sensor. It does show an option for cadence using my powertap hub, which is odd.

Hi David,

Then you have a very strange one-off problem. We generally don’t use cadence at all when testing. I would send in a ticket as well as log files (Documents > Zwift > Logs) of your rides if possible.