How does Zwift know how fast i'm going

Hello,

New to Zwift. My bike has a Stages power meter and a Garmin Edge bike computer. I’m on a basic Kinetic Road Machine. When I ride outside I use satellite data to give me my speed, and so don’t have a speed sensor. I can pair my Zwift up by Bluetooth to the power meter (I’m using an iPad) but while power shows correctly, my speed doesn’t go above single figures - I guess because Zwift isn’t receiving any data from a speed sensor on how fast I’m going.

Can anyone tell me how to set up Zwift within my current configuration so that speed is shown correctly and I can see my bike moving on the screen?

Thanks in advance.

Zwift doesn’t need to connect to your speed sensor. Provided you have your power meter paired to Zwift as the power source, you’re good to go. Zwift uses a complex algorithm to calculate your speed based on power, power to weight, gradient etc etc.

Note that the speed on Zwift won’t match what your speed sensor may be reporting. Speeds are a bit higher on Zwift.

As Nigel wrote, the speed sensor on your bike resting on a trainer on a flat surface is irrelevant.

Zwift calculates your speed on the course, in game, given your height and weight and the power from your pedaling something like how this calculator does: http://www.kreuzotter.de/english/espeed.htm .

Input your type of bike, your height, weight, road slope, height above sea level, etc., and it calculates your speed.

Thanks for the feedback. Makes sense. I’m just a bit surprised as I was setting up and testing my bike with Zwift on a flat course and was riding with a cadence of around 80, large chain ring on the front, close to the middle on the back, power output around 100W - gearings that would have me going at probably 25-28 km/h on the road. Zwift had me moving at 6-8 km/h on the flat (although it was a cobbled London street - maybe that has an impact). I’ll persevere with it. Maybe not a bad thing if I have to push it to keep up with the group …

Andrew,

Something seems off, when I am doing about 100 watts on the flats on Zwift I am doing around 17-18 mph on the Zwift TT bike. Watts are what makes you go within Zwift.

I tried searching for you on the ZML, but it seems you have only ridden for a very short time without enough data to go on to assist you.

 

Thanks Paul. Yes, I’m new. I only started setting up last night and I’ve cycled a total of about 500 metres, in my socks! It was all straightforward enough and the only issue was this speed reading. I did try out Zwift last year, once, using a borrowed Macbook Air. I had no issues with the speed at that time but I also don’t recall how I configured everything (though I did buy the Ant+ dongle and was using that, whereas now I’m communicating by bluetooth between the iPad and my power meter).

I will try to do a longer trial ride tonight and see if the speed issue resolves itself.

Zwift measures my wattage, but not always my MPH.  Thoughts?

Mike,

Stick to one thread please.

Mike, correct. Zwift isn’t interested in measuring your speed. It calculates your speed based on your power, your weight, gradient on Zwift then throws them into an algorithm to calculate your speed.

Zwift only needs to connect to a speed sensor if you’re using a dumb trainer and have no other power device i.e. power meter or smart trainer.

Another chance to do a quick test this evening. The same 100W power on a non-cobbled street had me at close to 30 km/h, i.e. exactly where I thought I should be. So I guess the cobbles resulted in a very substantial loss of speed, even on the flat. Thanks to everyone for their comments and advice.