Low power/cadence output from turbo trainer – please help

I am having an issue with my turbo trainer and power output that I would really appreciate some thoughts from the forum on a) what the issue is b) what’s causing it and c) whether or not it is possible to resolve or if I have to buy a new trainer.

I have scoured the internet for a post that describes the same thing, but can’t find one anywhere. I’m hoping someone on here can shed some light.

I’ll preface this by saying that the issues i describe below have plagued me on whatever software I’ve used (Trainerroad mainly, but Zwift recently too). But having recently bought a power meter to try to resolve the issue – but still encountering issues – I’m getting somewhere close to my wit’s end now.

This is an ongoing problem I’ve had since day 1 with my smart trainer, a Bkool Smart Pro 2, which I picked up new in late 2017. Now, I know that Bkool doesn’t have a great reputation in the smart trainer world, but actually most instances of erroneous power from Bkool trainers online report power outputs that are greatly exaggerated – an annoying side note in my ongoing struggle with this trainer.

The Bkool Smart Pro 2 does not need to be calibrated after each ride. In fact, you are unable to do so. Calibration is done by Bkool at the factory before it heads to the vendor. Or, as I will describe below, it can be done remotely after sale using computer software that allows Bkool to take control of your computer and recalibrate the trainer via a connected ANT+ sensor.

So when I unpacked the trainer in 2017, it was good to go straight out of the box. I set it up and did an FTP test. It was my first foray into riding to power (I’d never owned a power meter). So I based my target for the test on the numbers of the riders I was riding with at the time (somewhere between 250W and 300W). The test crushed me. No way could I hold anywhere near the numbers for an FTP in that range.

I did a number of tests over a week long period (I know, not best practice at all, but I was just starting out). I bought a fan, ventilated the room, read about 1000 wiki threads on FTP testing online etc. Finally returned what i considered to be an accurate FTP of 178. I used that as my benchmark on Trainerroad and went through several training cycles (Base/Build etc) building on that. HR was always in the right zones, VO2 Max sessions were excruciating, under-overs really mentally challenging etc. It was at the right level.

I increased power steadily up to about 208 over several months. By now I was racing crits and placing on tough circuits. A strong rider within a large cycling club. I told my racing buddies my FTP was about 200 (I weighed 72KG at the time) and they laughed their heads off. “Not possible” was the response. And it didn’t seem to be possible. We were racing together, I was placing ahead of them, they weighed the same as me, and yet they had FTPs maybe 100 Watts higher.

But it didn’t bother me enough to do anything about at the time. It was only a number I was using to train against. The training zones were all set relative to the FTP recorded on the trainer, and they felt in the right place. My HR corresponded perfectly to the intensities of the indoor sessions. And I was definitely becoming a stronger rider, getting PBs on my local segments every week. So who cared if the numbers indoors were correct. The training was doing the job and was all perfectly set relative to my maximal effort/power, whatever it was.

Then online racing happened. Game changer. Suddenly, having the correct number does matter.

I had taken some time off the bike (a year or so) and got back on it a couple of months ago, dug out the turbo trainer and did an FTP and ramp test. I got a result of 166. I figured this was about right. I had lost a fair bit from my racing form. And having been off the bike for a year, figured I’d need to get the legs pumping again to raise my level back up to where I started power training from.

But the issue was that on Zwift I was totally unable to ride with anyone. People from work who are not athletic (an I consider myself to be so) were doing rides on Zwift at a casual average of 200 watts. That would be me riding at about 125% FTP. For an hour. Impossible, right. I went up the mountain climb at a near maximal effort. I placed in the bottom 1% of more than 3000 people doing that climb that day. Even untrained, that was not realistic.

So I took it up with Bkool. They told me to check my weight on their site (it was accurate). To do another FTP test (yawn/eurgh). I finally convinced them that something was not right when I told them that my friend who rides with an FTP of 350 at a cycling studio he goes to had borrowed my trainer and could not hold 210W for more than 5 minutes.

They connected to the trainer and recalibrated it remotely from Spain. It took about 10 minutes, the ANT+ sensor had to be 10CM from the trainer, it’s all done via computer. I jumped back on the bike the next evening and did an intervals session and the levels were all the same, same exertion etc. No change.

So I bought a power meter to resolve the issue. After a lot of research I settled on the Assioma Duo (accuracy +/-1.5%). They arrived, i zero offsetted and then did a test. I connected the power meter to my Garmin head unit and the Bkool to Zwift and did an interval session. Here are the results (approximate):

Bkool vs Assioma
80W - 120W
145W - 245W
180W - 300W

That last one is my current FTP. Set at 180 on Trainerroad and Zwift. Measured at 300 by the Assioma Duo.

The discrepancy is approximately 0.6-1.0. Put another way, the Bkool is communicating only 60% of the power I’m actually putting out to the software I’m using.

This is commensurate with issues of cadence measured by the Bkool I have had. Now, I use an actual Garmin cadence sensor when riding indoors and outdoors. But when the battery died, I used the cadence recorded by the Bkool for a week. The cadence was also incredibly low. I spin at a high cadence in general (95-100 RPM is a good comfortable level for me). When I was spinning at that sort of level, the Bkool was registering 50 or 60 RPM. Interestingly, when I stood up and slowed my cadence a bit (probably around 75 RPM IRL), the cadence got higher and was more accurate – food for thought re where the issue here could be (weight and pressure being applied to the flywheel?).

Anyway, the obvious solution was then to use the power meter as my power source and select the Bkool as ‘controllable’ on Zwift or TR. And what a wonderful moment it was, to finally be able to ride alongside (and even overtake!) other riders in Watopia. A pure joy after killing myself on the bike to place in the bottom 1% every day.

Now I could hold 250W without much trouble (impossible before) and even hit the previously unfathomable wattage of 400W by just sprinting a little. Oh and there goes 500W with a sprint!

Problem solved, right? Unfortunately not.

Now I try doing an interval session with ERG mode enabled. My set up is: Bkool controllable, power source Assioma. I’ve set the FTP to 300W, which was the power output being shown from the Assioma Duo on my Garmin when I rode an interval on Zwift (with power and control connected to Bkool) at FTP (180) the day before. This number seems reasonable given where my peers are etc. And the Assiomas are correct to 1.5% – I trust them.

I’ve got power display set to 3 second average on Zwift (and on Garmin but that’s not relevant here, just for reference during my ride).

I do a zero offset on the Assioma app and on my garmin head unit. Then I start the ride with ERG mode enabled, but when the intervals start, the resistance gets totally confused. Now the Bkool forces me to put out TOO MUCH power?!?!? (weeps with despair).

Here’s the example. The target wattage is 100W. The Bkool holds the power from my Assiomas (connected to Zwift) at ~110. Target goes up to 120. Bkool holds me at ~140. This continues until the target is 180 and I am being held at an actual output of ~260. The screen is imploring me to “Reduce Power” – but I can’t! I slow my cadence and it just makes me grind horribly at that same wattage.

But interestingly, the difference is now inverse. Rather than only registering 60% of my power, now it is forcing me to put out ~40% more.

Of course, I could now start to train with ERG mode off, but I’d rather not.

I am really confused here and would so appreciate some thoughts on what is going on. It’s a complicated one and if anyone has actually got this far, then thank you for taking the time to read.

Key questions:
Where is the problem?
Can it be resolved?
Do I need to buy a new trainer?

Thank you!

hi @Joe_Gowdridge, welcome to the Zwift forums!

My first thought, are the Assioma’s set up correctly with Zwift? I have seen other users comment that if you are using the Assioma Uno with Zwift, not to enable the double power feature and that Zwift will double it for you. I don’t know if the Duo’s need any special settings for Zwift? Perhaps Zwift thinks you have only single sided power and is trying to double it, sending the wrong info to the trainer?

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No special settings needed in Zwift. Left pedal will send the combined power from Left and right.


Hi @Mike_Rowe1, thank you for your reply and your welcome! :slight_smile:

That’s definitely something to check, but I’m pretty sure it’s set up correctly. I am connecting using ANT+ to both Zwift and also to my Gramin head unit. I know there is an option to have the right pedal send the info to the left and then send that collectively to Zwift, but my understanding is that feature is used mainly to manage too many Bluetooth connections – I am connecting everything by ANT+.

On the Assioma app the options to double the power (explicitly stated as being for use only when you have an Assioma Uno) are disabled.

But the main reason I think this isn’t an issue is because I am getting the same numbers from my Assioma on the Garmin head unit as I am on Zwift – and the Garmin and Zwift are not connected together, but independently connected to the Assioma. Plus on my Garmin I’ve got cycling dynamics breaking everything own pedal to pedal. So I’m pretty sure this isn’t the issue. If it were, then I’d imagine i would see double the power on Zwift that i see on my Garmin.

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Time for a new trainer, methinks. Can you perhaps borrow someone else’s trainer to prove that?

Yes, I’m afraid you’re probably right @Steve_Hammatt.

One options I’m weighing up now is to use the low number from the Bkool as my set FTP on Zwift and then continue to train against that number for interval sessions. Then use my power meter giving my actual numbers for races.

Is that a possible solution? Would it have an impact on ZwiftPower?

You could try that.

So it’s only ERG mode now where it’s not working correctly? If so, then I can’t see why you wouldn’t be fine to race with the Assiomas giving your correct power to Zwift and Zwiftpower.

Zwiftpower’s FTP value is manually set and isn’t really used for anything there - what’s important is your actual race power figures, and that should be correct coming from your pedals.

Yes, exactly @Steve_Hammatt. Everything seems resolved with using the Assiomas as the power source except ERG mode.

Of course, I could just now start to do interval sessions without ERG. But I have to say, when you’re doing 3-4 interval sessions a week, having ERG mode there so you can just dial in and get on with it without having to focus too much on hitting the power targets does make those sessions more appealing.

My only wonder is about resistance going up hills in Zwift. If the ERG mode provides too much resistance, perhaps the Bkool also provides too much resistance on inclines in Zwift worlds? But even if this were the case, I can lower the Bkool’s resistance a little by reducing the ‘trainer difficulty’ setting in Zwift.

So when you say the FTP in ZwiftPower is manually set, does that mean it is not automatically imported from Zwift?

If that’s the case, then perfect. Because I am planning to record the power data from my interval sessions also on my Assiomas via the Garmin head unit, so I can then calculate actual FTP based on the data I’m getting from the head unit, if that makes sense. I could then manually update the FTP number in ZwiftPower.

Would that work? If so, I think that’s the solution here.

Correct, Zwiftpower doesn’t import your FTP from Zwift.

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Thank you! I think this is solved now then. :slight_smile:

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