Speed and Power Seems Extremely Low with Wahoo Speed & Cadence Sensor + Unsupported Rollers

Hi there,

This seems to be a common issue so I apologize for yet another topic like this. A quick rundown of my setup:

  • TacX Galaxia rollers (which I’ve selected as “unsupported rollers” with 700x29 tires in Zwift - though my actual tires are 700x35).
  • Wahoo Speed and Cadence Sensors (attached to rear wheel and pedal arm respectively)

In-game, I can’t seem to go much more than 5mph and will often max out at 2mph with an average of 80-100 RPM. I think this was giving me somewhere around 10 watts of power or so in-game. Trying some harder tests, even going 120-150 RPM only gives me about 14-20watts maximum.

It seems like the game is accurately picking up how fast I am pedaling (if I look at the in-game avatar, he will be pedaling like crazy while only going 2mph) but not giving me the correct power output.

I’m a complete beginner and have only ridden casually before trying Zwift so, to be fair, I don’t actually know what numbers I should be getting. But it seems that even for a decent amount of effort, I can’t seem to go very far in Zwift. It takes a lot of effort just to go one mile in the game.

Is there some setting I can change either in Zwift or with my setup? I’m not very concerned with getting accurate workout tracking at this point - I just want to be able to use Zwift to get a bit of exercise while indoors and then, later on, I’ll want to look into getting more serious about following a training regimen and tracking things.

Thanks for any help you all can provide!

Daniel, I wonder if this video from very well respected in Zwift community Shane Miller has any information that could help you? It appears that zPower does not correctly calculate your power from speed. Avatar speed in the game is determined entirely by the power which you generate (or which Zwift calculates that you generate from the parameters of your rollers).

Hey, Andrei, thanks for the reply. Actually, seeing Shane Miller’s videos is what originally got me confident that I could get a set of rollers and have a good time riding in Zwift. I was a bit skeptical at first that it would be possible or fun without buying a trainer.

But, unfortunately, my experience seems to be the complete opposite of his where Zwift seems to be overestimating his power generated. For me, I feel like it’s grossly underestimating how much power I am generating. It probably just is something wrong with my setup rather than with Zwift, but I was hoping maybe other people with a similar setup might know what it is.

Daniel, I have an idea. Try a different type of rollers, if available in Zwift, or pick any dumb trainer which has no power meter and which is not controllable. Anything else from the category of trainers which have to use zPower. I am guessing that Zwift may be using certain pre-defined settings based on known resistance of that trainer to convert your speed to power. I wonder if changing the trainer would change the speed-to-power curve and would enable Zwift to determine that you are riding at a higher power.

That’s actually a great idea - I’m not sure why I haven’t done that yet at least just to test things out. I’ll be a bit busy but hopefully I can try it tomorrow and report back with how it goes.

Unsupported roller is light for power output, it is to avoid having too much power, but it’s ok with roller who have not magnetic resistance

It’s not rpm but speed who determine power, so you have a problem with speed sensor or you are just slow, change gear

200W = 40km/h on your speed sensor with unsupported roller

I have Arion Mag roller with speed sensor, it work really well with good setup, you can have a good experience on zwift

Thanks for your input, Yann. I was hoping to get some concrete evidence from someone with a similar setup so I appreciate your reply very much, especially with the number of watts-to-speed you gave. What sensor model are you using exactly, if you don’t mind me asking?

Before trying @Andrei_Istratov’s idea, I ended up trying to reset my speed sensor and even replaced the battery. I still seemed to be getting the same results, unfortunately. I did end up ordering another set of sensors so that I could try to compare the results and see if the readings I’m getting from the Wahoo ones are accurate.

In any case, I did go ahead and try out setting my speed sensors to be paired with supported trainers in Zwift that use Zpower instead of the estimation that the “unsupported rollers” option uses. I didn’t do a thorough, scientific test but I did test every single supported trainer option as well as the “unlisted trainer” option. I found that for a lot of them, I had better results than before. Using a base of around 80-85 RPM at my lowest gear, I found options where I was able to output around 50 watts and get around 10mph in-game (depending on the terrain, of course).

So, for anyone that just wants at least a casual riding experience through Zwift and are having problems, definitely try out selecting and pairing one of the other trainer options when pairing your speed sensor - at least as a temporary fix. The ones I personally felt worked the best with my setup for how much effort I was putting in are as follows: BlackBurn Trakstand Ultra; Minoura RDA80-D; JetBlack Z2 Fluid; and Elite NovoForce. These are just what worked for me and only listed for reference. You will probably have to test these out with your own setup and see as all the trainers have very different power curves.

I’m still going to try out the new speed sensors and see if I can get something more accurate without having to result to this option but, for now, this works for me. I will report back when I’ve tested the new sensors. Thanks for everyone’s help so far!

No problem
I used whaoo blue sc sensor

Have you an apps for see the speed of your speed sensor ?
Or you need a speedometer for compared power ingame vs your speed on HT vs zpower curve you used

I can’t share a link, go on research and => “Elite Rollers Support” the first, 3rd comment 2nd link
It’s power vs speed for each HT on zwift

With my Arion Mag i have a power curve, if i respect her it feel to easy at low power so i used Tacx Blue motion ZP on zwift which reduced power under 444W compared Elite power curve.
With force 1 on my HT it feel real

Try to find the best with your config and not to overestimate your power output :wink:

A bit late but I thought I would give an update. In regards to @Yann_Marsal’s question, I do have an app to check my speed sensors but I’m not sure how to have it up while I’m cycling, unfortunately, so it’s hard to directly compare how fast Zwift says I’m going versus how fast the app thinks I am going. I would try doing some more tests, but honestly I just want to cycle at this point, haha. My max output with my setup seems to be around 60W so I’m nowhere near needing to dial it down. I wish I had the opposite issue so that I could to lower my output to match my effort versus struggling to maintain 10mph in-game at some points.

I did try some new sensors (Magene-branded ones, for those curious) and there doesn’t really seem to be any issue with the Wahoo ones I have as the readings seem to be about the same and the in-game power output and speed are nearly identical, as well. So I’m unsure about which part of my setup is causing Zwift to calculate such a low power output. I will say that I do notice with both the Wahoo and Magene sensors, that when I first start pedaling, my power output jumps from anywhere between 200W and 400W and then immediately goes back down to around 50W. I’m not sure if that’s an indication of anything, but maybe someone would know?

I haven’t been able to cycle this last week but I was able to get in a few good sessions that were fun. Unfortunately, my maximum output seems to be limited no matter how hard I am pedaling, with the options above. So things like keeping pace with another rider or deliberately trying to get into someone’s slipstream and all that are pretty hard to do and I usually don’t even bother.

As I said, if you’re looking for a casual riding experience or just a training session that is self-managed, my setup works perfectly fine for that. At the moment, I’m looking towards getting a power meter of some sort in the future unless someone can point me at some way to improve or fix my current set up.

How Gear you have on bike ?

Try with Minoura RDA2429-R L-L hometrainer in game
60W become 230W

Thanks, Yann, I’ll give that a try on my next session. It’s a 24-speed bike. I appreciate you trying to help me out - this has been a bit of a frustrating process to figure out. At one point I did go through and do a quick test on all of the different trainers but it’s possible I missed that Minoura one.