Use the speed my Kickr is sending via bluetooth rather than calculate it

My kickr sends a speed command via bluetooth.  I see it in the basic wahoo app and it appears to be pretty accurate based on my pedal RPM.

Zwift’s speed is nowhere near close to what I am doing.  If I pedal faster, the speed stays the same.  If I slow down quite a bit, the speed stays the same.  I have to put my rpm in the mud before Zwift’s calculations make a difference on speed.  I dont really care what other people’s speed is, I want to see feedback on the screen based on what I am doing.

Speed within Zwift is calculated using Watts, your weight, your trainers power curve, the bike you are using within Zwift and the virtual elevation changes. Your rear wheel speed has nothing to do with the speed within Zwift (except for producing Watts) and will very seldom match your in-game speed.

Does the watts change you pedal faster and slower? Are you sure the trainer are setup correct?

Gerrie - yes the watts as displayed in Zwift change as I pedal faster and slower.  But there will be hardly any speed change over a range of 200 to 500 watts.  The kickr has the latest firmware and I do a spindown every time I ride it.  Right now there is such a massive disconnect between Zwift’s speed and my Kick’s speed I wonder if the Zwift algorithm is working at all.

Paul - Zwift ought to be able to properly calculate a proper power requirement for an x kg rider going up a y percent incline at z mph.  If my Kickr says I’m going 20 mph up a 15% incline, Zwift ought to say “Here’s 900 watts for you, chunky guy” and my speed will change accordingly until an equilibrium is reached.

Bill, do you want to share the link to the strava file. 

As Paul said there is no correlation between wheel speed and speed in game. but as the Power (W) change your speed should change.


I am trying to let you know how Zwift works. As I have stated your rear wheel speed has nothing to do with in game speed and you are the one who controls how much and how little watts you put out. Please ignore the speed of what your Kickr is saying, it has no relevance. 

Here is a link to the knowledge base:

Here is a link to the unofficial manual:

Gerrie - I dont have a Strava file for my rides since I’m not really a Strava-er.  But if it would help I could make a quick one and provide it to you guys.

Paul - Thanks for the links.  I do understand the gist of how the Zwift does its calculations.  This is my “Feature Request” forum and I was hoping Zwift could incorporate better speed feedback to the user based on all the signals being sent to it.  In the case of smart trainers that send Zwift a speed, I dont see the use for Zwift calculating the speed since the speed is being plopped into Zwift’s lap.  Zwift should be able to take what I am giving it and send a proper signal to the Kickr and through differential equation goodness a steady state speed and power requirement will be reached.

Anyways, this is my request and if it cant be done then that’s cool.


Smart Trainers do not send any speed information to Zwift, just watts and cadence (Zwift sends info back on grade if controllable trainer is selected).

I don’t see your request getting implemented since rear wheel speed can be manipulated even easier than watts, plus Smart Trainers have a limit to how much elevation they can simulate.

I understand what you are asking for, but it’s not very practical in the Zwift virtual world. 

Hi Bill,

Paul is correct - the KICKR (and all smart trainers) do not send a speed measurement. They send a power measurement (in watts) which is what we use to calculate your speed in game.

Whatever speed is being displayed on your computer or Wahoo app does not take in to account all the virtual factors of Zwift (air resistance, wheel choice, bicycle choice, CdA, draft, road resistance, etc…) and will never match quite properly.

One of the most important factors in the speed calculation in Zwift is rider weight, which the KICKR does not take into account for it’s speed measurement. I know some guys that weigh 50-60 pounds more than me and can crush me on wattage alone, but they can’t keep up in the real world because their power output does not offset their additional weight, at least not for long enough to beat me up a mountain. Zwift takes this into account by basing speed primarily on watts per kilo, which was a really smart decision on their part.