Am I doing something wrong?


(Nathan Creedy) #1

Hi all, just joined the forum this evening hoping someone can help me out…

I am reasonably new to Zwift and have question regarding the speed and distance calculations that are occurring.

My setup is a road bike on a JetBlack M1 Pro (NON smart trainer).
I have the following sensors:
Wahoo Tickr arm/wrist HRM
Wahoo RPM Speed Sensor (mounted rear wheel hub)
Wahoo RPM Cadence Sensor (mounted left crank arm)

I am saving to buy myself a ‘smart’ trainer, but using my current rig to see if I’m going to enjoy this whole experience enough to justify the expense.

Now, I understand that I am riding a non-smart trainer so there is no feedback through my trainer regarding resistance or incline/decline information, but when Zwift is reporting that I’m riding a fairly flat road (2-4%), and I’m doing 70-80 rpm as reported by my cadence sensor (which I believe) on my big chainring, and my 11 tooth rear sprocket, Zwift is reporting that I’m doing no where near the speed that I would be on the open road.

As an experiment to see if my sensors are working properly, I collected data from a ride in the generic Wahoo Cycling app with the same bike, same sensors. It took me 2:30 to ride 2km’s at approx 88-90rpm which works out at an average pace of 47.4km/h - this relates to what I’d expect out in the real world.

So my question,
Why is Zwift changing my reported speed when I’m NOT on a smart trainer?
Why doesn’t it just report the actual speed that my sensors will be giving it?

It’s quite disheartening to be working so hard for so little ‘reported’ effort. 25mins to do 8km’s on my fastest gearing at 70-80rpm? Something not right there…

Any help on this would be greatly appreciated!


(Daren Chandisingh [Vision]) #2

Did you select the correct trainer from the “dumb” trainer list? I’m not even sure Zwift supports your trainer’s power curve. The “JetBlack M1 Pro” isn’t on the list here:

https://support.zwift.com/en_us/which-trainers-does-zwift-support-By_k0JHQ

I guess there’s a question of the resistance being used here. I mean a wheel going round at 200 rpm against no resistance is a different amount of power being used than the same wheel revolving at the same speed against a greater resistance. I don’t know how that gets dealt with.

There’s a good article covering virtual power here:

If you read that, you’ll see it repeat the importance of selecting the correct trainer. If yours isn’t supported, I don’t think there’s any way you can rely on the results.


(Paul Allen) #3

Speed within Zwift zpower is deterbined by: the rear wheel speed of your bike, the power curve of the trainer selected on the pairing screen, this is converted to watts and with that and the in-game bike used, in-game weight, in-game drafting and virtual elevation changes your in-game speed is determined.

In your pic posted from within Zwift you are going up a virtual incline which will reduce your in-game speed. Smart trainer or not, elevation changes will have an effect on in-game speed.


(Nathan Creedy) #4

thanks for your responses!

I understand what you are both saying, but if I’m not on a smart trainer, why does the program assume I’m going to slow down, instead of assume I could be doing the speed as indicated by my sensors, but working harder?

In the meantime, I have looked at the list of trainers as per first response above, and noticed that although they don’t list the M1 Pro specifically, they do list the M5 Pro, and they appear to be identical trainers. I’m wondering if the M5 is just an updated version of the M1?
I have changed from an ‘unsupported’ profile to the M5 Pro and as Zwift is telling me, I’m riding it on it’s 5 level of resistance.


(Paul Allen) #5

Because Zwift speed is based on watts and to a little greater extent w/kg. It’s not going to match your rear wheel speed, if it did you would be flying up the hills and mountains. I use a power meter without a smart trainer and I slow down going up hills/mountains and speed up going down, just like in the real world.

Been using Zwift for over 3 years, it will take you a little bit to wrap your head around how everything works.


(Gerrie Delport) #6

So looking at the graph below you will see Speed vs power for a random trainer, Zwift has the curve for each type of trainer. So your speed sensor tell Zwift what speed your wheel is doing then Zwift can read from the graph at that speed what power are generated, so at 28km/h you generate 200w. Now we have watt (power) same as what a power meter or smart trainer would send Zwift. Now Zwift will take the power number and calculate how fast you will be riding with that Power (200w) on the incline also taking into account your drag weight ect. Then it will show that speed and your avatar will go at that pace. So if I use bikecalculator.com to calculate the speed up a 3% incline for a 80kg rider producing 200w it give me 18.7km/h. Zwift does all this in a fraction of a second.