What’s the best way to use Zwift with a stationary bike? I have a Bowflex C6, which reports power and RPM over Bluetooth. However this doesn’t seem to work well because zwift can’t control the resistance. I can manually change the resistance on the bike to meet the target wattage of the workout but I have no idea if that’s the “right” resistance. How do I determine if I’m using the bike and the app in the most correct way?

  • "I can ... meet the target wattage of the workout" - that's really most of what all smart trainers do, just automatically. That is doing it the correct way. May 31 at 0:08
  • Is it accurate? Like if I’m pedaling at 85 rpm at a resistance level of X and my output is 100w, is that roughly equivalent to the same wattage I’d be outputting on a road against the same resistance? Most sites say “no”. May 31 at 2:41

"I can manually change the resistance on the bike to meet the target wattage of the workout"

Well, that's the right resistance then. The only difference between that and a smart trainer is the smart trainer does it upon computer control instead of you shifting gears or adjusting a dial on a resistance unit. That's really all there is to it.

Is it accurate? Like if I’m pedaling at 85 rpm at a resistance level of X and my output is 100w, is that roughly equivalent to the same wattage I’d be outputting on a road against the same resistance? Most sites say “no”.

Ignoring the aspect of instrumentation errors and small difference in measured output from aspects such as how it's being measured, then the answer to that question is basically yes. If you are claiming "most sites" say no then you are likely reading answers to different questions.

Reading into this question, I think you might be confusing what 100w into the pedals will do in real life vs how your in-game avatar rides, with regards to speeds or climbing, etc. That relationship is very loose, but Zwift is a video game, it doesn't need to, nor will it ever match reality exactly. Please comment if that is what you are referring to.

However, for workouts, watts are watts. 100w on the trainer is no different than 100w on the real world. If you are riding at 100w at 85 RPM at resistance X on the trainer, you'll do that. If you are on the road, and are putting 100w in at 85 RPM, you'll accelerate until air resistance, gravity on a slope, or other rolling resistance equals 100w at which point you'll then maintain a constant speed.

So, in short: if Zwift says to ride at X watts, and your bike says you are riding at X watts, then you are good to go, simple as that. (assuming your trainer is reasonably accurate and calibrated).

  • This is how Zwift works with "dumb" trainers, but X watts generated at higher crank torque and lower cadence is not always the same as X watts generated at lower crank torque and higher cadence: you can often see this by differences in heart rate and breaths per minute. But, in general, yes, X watts is nearly the same as X watts no matter how it's generated, which is what should matter to the OP.
    – R. Chung
    May 31 at 13:04

You're right - this is fundamentally impossible to make perfectly "right"

The correct answer is to have a fancy trainer that measures your power output in watts, and increase/decreases the resistance automatically based on what the software tells it, which is derived from the gradient and wind/weather conditions for your current virtual location, by the software.

To be "fair" you should wind up the resistance when going up a hill, and set it back to "normal" for the flats. However gauging and calibrating these settings is hard.

If you have a road bike with a power meter, try an FTP test for real outside, to get an idea of your true wattage on the flat. This is a horrible test and even the short versions will leave you exhausted. Try and "memorise" that level of physical effort.

Then ride your indoor bike and aim for the same input effort, then adjust the resistance until it shows the right power output. That is your new base resistance setting - mark it somehow.

For uphills, its a bit more guesswork. Find another rider who is about your speed and power while on the flat. When you both hit a climb, increase your resistance knob setting so that your speed and power matches your target rider's stats. This value will only work for this gradient, so mark your resistance control with this gradient.

Now if that slope was 6%, you can reasonably double the resistance increase to equal a 12% slope, or halve it for a 3%.

If that's too hard, just remember zwift etc is all fake riding, and that you're only really competing with yourself. So work on improving your own times and ignore everyone else's.

ON SECOND THOUGHT* Do you need to make any changes at all? Your bike returns "power in watts" to the app. If you're riding up a virtual climb, does your forward speed drop compared to a flat ride at the same power?

If yes, then you don't need to change anything for the app to read you right. The only downside here is that it doesn't accurately represent any form of realistic training for climbs. Sure its a lot nicer than riding in the rain, but remember it's gamified, not real.

  • It might be the last thing. The bike has its own resistance knob and digital representation of that resistance (a numerical scale between 0-100) and the bike reports RPM and power in watts to the app. When I change the resistance, the watts immediately changes at the same RPM. May 31 at 3:09
  • @RibaldEddie: can you feel the resistance change immediately too? May 31 at 3:34
  • @whatsisname yeah May 31 at 3:39
  • @RibaldEddie: then it makes sense what the bike is reporting. Keep in mind, Zwift by default shows an average over the last 3 seconds, which may explain some discrepancy in what you are expecting vs what you are observing? You can change that in the zwift settings. May 31 at 3:59
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    @RibaldEddie: sure, 2.4w/kg isn't great by pro-racing standards, but you're close to being in C category, and remember that most of Zwift users are pretty hardcore, so don't get too caught up comparing yourself to them. May 31 at 4:50

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