Author’s note: A stationary indoor bike will be accurate in Zwift with a power meter. This article is about comparing a “spin bike” (which is a trademarked term) with a power meter to the same bike with a simple speed/cadence sensor.
From time to time I see questions on using a stationary bike in Zwift. More often than not, the advice given is “grab a cadence and speed sensor and you are good to go”. The well-intentioned suggestion utilizes the option Zwift provides of using a speed and cadence sensor with a non-smart classic trainer.
Essentially Zwift has tested certain non-smart classic trainers and those supported trainers have a lookup table in Zwift. Basically. for X speed, you’re doing X watts. It’s a power curve table. For Unlisted/Untested trainers they have another lookup table, but probably based more on averages that may or may not be accurate. There’s a lot more to it, but I’ll invite you to read the excellent Zwift Insider post about virtual power vs going over it here again.
The Challenge with Stationary Bikes
Connecting a stationary bike as a trainer on Zwift can be a problem, though. Here’s why: a trainer has a set resistance (the pressure of the roller on the back wheel) and your speed increases with your wattage via gear changes and cadence, whereas a stationary bike has speed that is dependent only on cadence (no gears). You can change resistance manually with a knob, but if you maintain the same cadence, you will maintain the same speed and thus, the same Zwift estimated power, regardless of where the resistance knob is set.
To put that a different way, as long as you pedal at the same cadence on a stationary bike, your flywheel will spin at the same given speed. The way you increase the wattage on a stationary bike is by putting resistance on the flywheel, resulting in more wattage to keep the flywheel going at the same speed.
It’s worth mentioning here that resistance on a classic trainer can also be highly variable depending on how tight or loose the roller is against the tire. Classic trainers have to have the roller tightened against the wheel to the trainer’s spec in order to be anywhere near accurate in terms of wattage. So it can basically be as variable as a stationary bike would be, although you can’t just reach down and tweak it on the fly. Anyone who has experimented with that knows that the looser a wheel is against the roller, the higher the reported watts will be, and vice versa. Hence the reason proper tightening is so crucial.
Back to the stationary bike. When Zwift is estimating power solely by a speed and cadence sensor and knows nothing about the resistance knob, that estimated power number will be wrong. It will be wrong because it’s missing an enormous part of the equation, the resistance, something it knows for a trainer, but can not know on a stationary bike.
Spindown for Stationary Bikes
How could Zwift know resistance and have accurate zPower with a stationary bike? The only way I can theorize it working is to have a spindown test within Zwift. Set the stationary bike resistance to where you want to ride, do a spindown to determine resistance, then keep the resistance at that setting the entire ride, using only cadence to make changes in power.
Not a great way to ride, and Zwift would also need to know the stationary bike gear ratio (or use the speed which the stationary bike displays) for its calculations.
Testing Stationary Bike Power Accuracy
Enough explanation, let’s see it in practice. To illustrate why a stationary bike isn’t accurate in the Not Listed trainer setting, I set up a few testing scenarios. I set up a single Freemotion stationary bike with a Stages power meter and a Wahoo speed sensor. I then set up two Zwift sessions, with exactly the same height, weight, bike, wheels, gender, FTP, etc. I paired the speed sensor, HR sensor, and cadence sensor to one session via ANT+. I then paired the power meter, the same HR sensor and the same cadence sensor to the other session via Bluetooth. The same pedalling effort would go into both sessions, power would just be output via different sensors.
To put this into a visual format:
| Session 1 | Session 2 | |
| Name | Harry Legz | Scott DeLeeuw |
| Stationary bike | Freemotion s11.6 | Freemotion s11.6 |
| In-game bike | Zwift carbon w/ 32mm carbon wheels | Zwift carbon w/ 32mm carbon wheels |
| FTP | 197 | 197 |
| Gender | Male | Male |
| Height | 5’ 10” | 5’ 10” |
| Weight | 177 lbs. | 177 lbs. |
| Cadence input | Stages power meter | Stages power meter |
| Heart rate input | Scosche Rhythm+ | Scosche Rhythm+ |
| Power input | Wahoo speed sensor, “Not Listed” trainer, 20” wheel setting | Stages power meter |
| Connection format | ANT+ | Bluetooth |
Note: the FTP setting was lowered to see if either of the tests would result in an FTP gain that wasn’t warranted.
For the first test I set up a MeetUp on Watopia Flat between myself and my identical twin nemesis Harry Legz. I configured the MeetUp to include only the two of us so variables like drafting did not come into play. My first test was a cadence test. I would do 2 minutes with no resistance at all at 70 rpm, 80 rpm, 90rpm, and 100rpm. Then I would repeat these same 70, 80, 90, and 100 rpm tests, but with about 130W of resistance on the knob.
The graph below shows the comparison. Cadence was the same as they were coming from the same sensor:
| No resistance | No resistance | 130W(ish) actual power* | 130W(ish) actual power* | |
| Speed sensor zPower | Power meter | Speed sensor zPower | Power meter | |
| 70 rpm wattage | 130W | 41W | 128W | 134W |
| 80 rpm wattage | 174W | 51W | 170W | 136W |
| 90 rpm wattage | 209W | 61W | 213W | 135W |
| 100 rpm wattage | 276W | 54W | 270W | 124W |
*Note: I adjusted the resistance knob on each cadence change to maintain 130W(ish) via the power meter reading.
When I turned the stationary bike’s resistance knob to around 130W(ish) actual power, the results were pretty much exactly the same for the estimated power coming from the speed sensor as they were during the no resistance test. This is expected since the cadence was the same as the first part of the test, and if the cadence is the same, the speed will stay the same. The graph below shows the data comparison visually.
One interesting observation on the no resistance test: true wattage actually went down at 100 RPM. Since the watts are measured with a crank power meter, my take on that is the momentum of the flywheel started to take over, pulling the pedal through. I was pedaling faster, but softer.
As you can see, there is a very large discrepancy in actual power vs estimated power, over 200W at some points in the graph, but what did it do for the ride stats?
Watopia Flat Route, ride time 23 min 24 sec
| Speed sensor zPower | Power meter | |
| Distance | 5.48 miles | 4.03 miles |
| Avg Power | 195W | 75W |
| Max Power | 400W | 162W |
| Avg Speed | 20.1 mph | 14.8 mph |
| Max Speed | 30.5 mph | 23.8 mph |
For the very same pedaling effort, the speed sensor rider covered a mile and a half additional distance in just 23 minutes! That is almost 30% more!
Just for fun I also tested what would “MAX” out the 400W estimated power on the stationary bike. That happened around 115rpm. As long as I maintained 115 rpm, regardless of resistance, I would peg 400W in my Harry Legz session. (It’s worth noting that I could do 400 estimated zPower watts at around 50W of actual power, if the resistance was dialed down on the stationary bike.)
The cadence test is all fine and dandy, but I wanted to see what difference this made during an actual ride. Maybe one with an interval workout incorporated into it to see actual larger power hills and valleys and how they would track between both setups. Once again I set up a single Freemotion stationary bike with a Stages power meter and a Wahoo speed sensor, then rain two parallel Zwift sessions just like the first test.
For the actual ride I set up a one hour MeetUp on the 5.7 mile Watopia Hilly Route for the two sessions. I set the MeetUp to include only the two of us so variables like drafting did not come into play.
This was my ride format:
- 20 min warm-up
- 5 min at 190(ish) watts
- 5 min rest
- 5 min at 190(ish) watts
- 5 min rest
- 5 min at 190(ish) watts
- 5 min rest
- 10 min cooldown
The result of this match-up? Remember this is input from one bike. My nemesis Harry Legz lapped me on Zwift KOM just as I was starting lap 3 of Hilly Route, rocketing past me at the finish banner. He also took second fastest time (I honestly felt bad about that) on Hilly Route. At the end of the ride/workout, he received a nice fat FTP gain, despite only about 15 minutes of a moderate 190W effort.
Let’s look at the data.
Watopia Hilly Route, ride time 1 hour
| Speed sensor zPower | Power meter | |
| Distance | 21.73 miles | 15.11 miles |
| Avg Power | 254W | 132W |
| Max Power | 400W | 264W |
| Avg Speed | 21.4 mph | 15.0 mph |
| Max Speed | 38.7 mph | 36.1 mph |
| KOM time during 110W 90rpm warmup | 3:29.16 | 6:52.69 |
| Villa sprint time during 110W 90rpm warmup | 34.22 sec | 44.76 sec |
While these numbers look dramatic, the graph of the power difference looks even more dramatic:
This graph does look more interesting at first glance than I thought it would. zPower is about 100-200W high as before, but the power curves parallel each other more than I first expected until I really analyzed the data. Why is that? If you notice the cadence line I was soft pedaling at around 90 or so rpm for the warmup, rest intervals and cooldown. During the intervals themselves my cadence would go higher to 100-105 rpm. Since zPower is being estimated by speed, which is directly related to cadence on a fixed gear stationary bike, this makes perfect sense. A jump in 10rpm made a massive difference in zPower because it was making a big jump in flywheel speed. It was simply a coincidence that my higher true power was done at a higher cadence and that higher cadence gave a higher zPower number.
Searching for Sweet Spot
Discerning Zwifters may wonder if there’s a “sweet spot” on the stationary bike’s resistance knob where zPower and true power converge across a usable cadence range (say, 70-100RPM). Or to put it simply: can we make the zPower number be close to accurate on a stationary bike?
The answer is: not really. Not without actively varying the resistance knob, and having a power meter to check your accuracy. (Of course, if you have a power meter, you don’t need a speed or cadence sensor or zPower anyway.)
On my first cadence test when I had 130W of resistance on the flywheel and was pedaling at 70rpm, the numbers were nearly identical. On the second test, if I had maintained about 85rpm in my 190W intervals power would have tracked closely. I could have also cranked up the resistance to 400w and spun at 115rpm (for the whole minute I could maintain that). But without a power meter I would have been guessing that the numbers lined up and inevitably what would happen is you’d loosen the resistance knob and drop actual power, but zPower would stay at 400W since your cadence isn’t changing.
Conclusions
So there you have it. I had fun doing this test. It might seem pointless, but I wanted some real world data for when the suggestion is thrown out to just use a speed and cadence sensor with the Not Listed trainer setting on a stationary bike. Seeing this data I don’t think it’s a good idea. I get that it’s inexpensive and not everyone has the money for a power meter, but you are missing the resistance part of the estimated zPower equation. Because of that, the power estimates are at best a guess, and a bad one at that.
None of this is to say a stationary bike is a bad idea for Zwift, a stationary bike can be a GREAT tool for Zwift. If you have multiple riders in the family, or just want the simplicity of hopping on and riding, a stationary bike may just be the ticket. But please reconsider the incorrect speed and cadence route and set it up with a power meter such as a Stages crank or power pedals like the Assioma UNOs. There are inexpensive options if you look around.
I agree with the purists when they say a stationary bike won’t get resistance changes from Zwift, but Zwift will use the power you are putting into the bike to adjust your speed up and down in the game, the same as if you were riding a bike outside that dynamically adjusted gears to keep your cadence the same as you hit uphills and downhills. Stationary bike or smart trainer, the true power you put into your pedals is what determines your speed in the game, the gradient feel is icing on the cake.
I wrote another article about an inexpensive stationary bike setup that will work with Zwift that can save some cash over the long haul. I found my entire stationary bike, with power meter, for $200. If you are thinking about going that route, it’s worth taking a look.
Cadence and speed sensors on a stationary bike – summary
Pros:
- Inexpensive
- Can do rides and give Ride Ons
- Breaks up the monotony of indoor training
- Could be a gateway to a great Zwift future
Cons:
- Not what Zwift intended with the speed and cadence option
- Isn’t accurate, missing the resistance part of the equation
- Not useful for personal fitness improvement measurements since zPower is only tied to cadence/speed, not how many watts you are actually producing
- Can not do training plans as power targets are only tied to cadence/speed, not resistance
- Will be very disheartening if you ever go to a power meter or smart trainer
Questions or Comments?
Share below!
I have used a Spin Bike since I first started using Zwift in the spring of 2016. I have put 27,040 Kilometers on it while doing Zwift. I do, however, have PowerTap P1 pedals installed on the Spin Bike. My reasons for getting the Spin Bike are the whisper quiet belt, I needed to be able to ride it while my wife slept. The lack of electronics, Facebook is filled with people talking about all the problems with smart trainers. The safety of a solid front wheel. I have grandchildren walking around and don’t need a dangerous wheel and chain spinning around. There are… Read more »
Completely agreed that a spin bike with a power meter is a great tool for Zwift. That’s exactly what I use. I wanted to show the difference between spin bike and power meter vs spin bike and speed/cadence sensors.
Hello! I just acquired a Stages SC3 which has a power meter and I’m very excited to get started w/Zwift. Are there any rides you recommend for someone new to the platform?
Also, strategies/approaches for accurately adjusting resistance manually on the bike to follow along with the Zwift courses?
Hi Mel, you don’t really need to unless you want to. Zwift will automatically adjust your speed to match your power output and the terrain. With Zwift you are essentially just riding a fully automatic bike.
Thank you Scott! You just solved a great riddle for me. I’ve been trying for 130 Zwift races and 2 years now to go from a Zwift C rider to a B rider. I’m also trying to figure out how to motivate Zwift HQ to fix their very broken racing system and have riders riding in their proper categorization. A riders keep crashing C races and screwing up the race dynamics. But this article just made a giant light bulb go off. I’m gonna sell my Wahoo Kickr and buy an exercise bike! I’ll immediately be an A Rider on… Read more »
Unique problems require unique solutions. You’re doing better than me, I’m barely hanging on in C. An exercise or spin bike with power meter will be accurate in Zwift, so if you go that route make sure sure you do only speed/cadence to guess power. 🙂
Apologies Scott. My post was 100% sarcasm. Which doesn’t translate well in mssg board text. I appreciate the time you took to perform this analysis and share it with us.
As I know, Zwift only care about power, if we put https://buy.garmin.com/en-US/US/p/606555 into a spin bike, can we have a accurate measure in the game on the power?
Yes, definitely, an exercise or spin bike with power pedals/crank will be accurate in the game. Zwift cares about watts.
I appreciate and agree with this article, and especially w the premise that an existing spin bike is way less expensive to get a start on Zwift or Rouvy etc. That being said, I rode around 50 hours, close to 1000 “miles” on my professional quality Spin bike used in a large metro spinning studio before “I saw the light and rec’d a ” proper trainer” for my birthday: (Kickr Snap) long story short, my 400 watt maxes went the way of the dodo bird, and my 370 Zwift assigned ftp as well! I mentally and physically struggled with my… Read more »
I think letting them spin around without inflated expectations is a really solid idea. In my testing, I knew both testing sessions were coming from the same spin bike and pedaling effort. But I would watch my session with my power meter and think “why are you so slow”, the speed/cadence session was a rocket. I was fortunate to buy a spin bike with a power meter included, for cheap, I know others aren’t so lucky. In your case, starting with speed/cadence helped you gateway to a bright Zwift future.
I use a Keiser m3i which is a great spin bike. Quiet, smooth etc. Keiser does sell a Bluetooth dongle which will send out your power output. I had nothing but trouble with it (would work great then start intermittently cutting out mid way through a ride, super frustrating). Their support was great but we could never get it sorted out. I switched to Assioma pedals and have never looked back.
Also had the same issue with the Keizer m3i. I returned the M3i and bought the Wahoo KICKR Bike. Best decision ever. The number of F-bombs per Zwift ride dramatically decreased. However, for someone who isn’t a Zwifter, the Keizer bike is a great spin bike.
queue the ZP people trying to justify…. put them on a kickr or neo, and see the reality bite
Agree, Dan. I had an extremely inflated opinion of my abilities based on the numbers ZP assigned to me, which came crashing down in flames on my first “real” ZWIFT ride. Took me two and a half months to climb to 154 FTP. Now I know why there is so much animosity aimed at ZP riders. Too bad we couldn’t have all ridden together in an overlay world without approved trainer riders.
My Tacx Blue Matic gives the exact same numbers as the Elite drive in the gym. So the set up is important.
I have a Schwinn IC4. It transmits a power number to Zwift that is calculated using algorithms similar to ZPower. The bike’s console calculates the power number based on cadence and resistance level. It is highly inaccurate. I have seen the bike transmits power numbers that are anywhere from 50-150 watts higher than my P1 pedals transmit on a side by side test. It is true that the only way to have a spin bike transmitting accurate numbers to Zwift is to use power meter pedals, unless of course, you have the money to buy an indoor smart bike
Yup I got an IC4 last Sept — great way to start. Moved up from D to B and then when I was averaging 300+ watts in a hour race — looking like I was going to be bumped into A group — I figured that the bike was off. So with power meter pedals — I now average 200 watts on a long ride — so the bike was off by easily 33%. If a person is not into racing and just wanting to cycle around in group rides and workouts then the bike by itself is fine.
You have the sentiment right, but it’s more complicated than that. Unfortunately Zwift doesn’t know it’s a spin bike as they are using the Classic Trainer setting, there is no spin bike setting. My personal feeling is the ZPower limit of 400W is too high. I get what Zwift was doing, they probably wanted people to be able to sprint up to 400W. Unfortunately what you see instead is many using zPower are spending entire rides near 400 zPower watts. I used the 20″ wheel in my tests, think about using a 700c setting. A realistic solution is to limit… Read more »
So why are the true power numbers on a spin bike so low ? I use my Giant defy with speed and cadence sensors and my numbers are the same as on the Elite drive in the gym.
The true numbers are accurate, and some people aren’t used to seeing that with incorrect setups and inflated numbers. A spin bike will never work with speed and cadence, it’s a fixed gear and resistance at a knob isn’t part of the ZPower equation. Think about it, Zpower is being calculated by speed, a spin bike is a fixed gear so speed and cadence are always tied to each other, you can completely remove resistance and keep the same speed and high Zpower number. Also, I have no doubt that you’ve painstakingly gone through your setup to ensure it’s accurate,… Read more »
Three questions…
HI Scott, great name by the way! 1) Heart rate isn’t figured at all into the zPower calculation. Calories, when power data is present, are calculated with that data. With heart rate it’s more of a guess. This TrainingPeaks article will shed some light. https://www.trainingpeaks.com/blog/how-accurate-is-that-calorie-reading/ 2) In layman’s terms, pedal based power meters have internal strain gauges. They look at the torque being applied, then use that with your distance pedaled and cadence to come out with your total watts. Force through a distance divided by time. A cadence sensor only has the cadence portion of that, it knows nothing… Read more »
Hi Scott, Great article. I’m not a zwift rider yet but eager to get on. I’ve been looking for a inexpensive way to get on Zwift but also share a bike with my wife who wants to try some basic virtual spin classes. I ride a dumb trainer now and was considering upgrading to a smart trainer but I’ve been reading through your other article on the Freemotion &AD200 and that would work for both of us. In your experience do all the Freemotion S11.9 have the power meters and any issues connecting with Zwift? Thanks!
I highly recommend the Freemotion bikes if you can find one economically. I *think* they all have power meters as they were spin studio bikes before they split from Stages. But you can look at the left crank, if there’s a big box on it (look at the power meter pictures of the Stages SC3 for a preview of what it looks like), then it has a power meter. If the Freemotion console reads watts that’s also an indication as that is only from an ant+ power meter on the Freemotion bikes. Look all the way back to an s11.6,… Read more »
Thanks Scott, really appreciate it! I will keep an eye out for sure, currently just spin gym resellers asking around $800.
Canadian dollars that is, going to use a Sunny Health with a wahoo cadence until then.
Hi Scott, I hope you still monitor this thread, as it’s the only one that seems like might be able to help me. I came across this article while trying to figure out how to connect my Freemotion spin bike to Zwift. It has the AD200B power meter, and the console does show watts. However I have no idea how to connect it to Zwift. I purchased the Garmin ANT+ stick/dongle to attach to my Samsung tab but it doesn’t seem to pair? I honestly don’t know how to though. The console will connect to my Garmin Instinct watch and… Read more »
Hi Steph, it should pair up if the ant+ dongle is working. There are other apps, like ANT+ Plugin Sampler, you can use to see if the dongle or bike are found just for troubleshooting purposes. Feel free to email me scott dot dl @ gmail if you want, I have lots of experience messing with that.
Oh, and zero issues connecting to Zwift with ant+, it’s about as easy as you can get. 🙂
Hi Scott,
What about a Raspberry Pi calibrated to the spin bike to accomplish simulated power? There are developers who offer code for the android device.
And would that still be considered zpower? Thanks
Hi Joe, I don’t know specifically about the Rasperry Pi calculating power, but unless it knows the resistance it probably isn’t too accurate. Power is a product of torque, distance and time, if the Pi doesn’t know the torque number then it’s just an estimate. It wouldn’t be zPower technically, as it’s presenting a power number to Zwift, but probably calculating the same.
just discovered HR2VP (https://bipr.fr/training-with-heart-rate-to-virtual-power) which uses the actual HR to match the power within Zwift. Seems to work surprisingly good when comparing to power meter pedals (https://www.youtube.com/watch?v=wCBe9t0AXdc). Only a delay of 5-10sec between increasing power to displaying and experiencing in Zwift are to be expected.
Already tried it with my Schwinn C8 and this made my impressions much more positive then only Zwifting with completely inaccurate power output
Hmmm, maybe it’s close. But I know from experience that my h/r isn’t always associated to my real power. Like Scott says, torque is the only way power can really be measured accurately. Take a look at Assioma UNO for an inexpensive way to add power to your C8, if pedals can be switched out.
Completely agree! For me as a hobbyist it was/is simply a much cheaper way compared to an actual power meter attached.
Color me skeptical, but how does heart rate match power in any sort of way? Even knowing heart rate zones and maxes that still really doesn’t correlate to individual power right? For instance, one person could be in zone2 at 80W while another is in Zone2 at 250W. How would this algorithm calculate accurate power?
that is actually a pretty good question and I was sceptical as well. I saw that the result matched best if I used real results from former FTP tests with power meter (before-pandemic-gym-times). You can use them as reference for the algorithm to do the “magic”. As I’m only using it as a somehow comparison to those former times maybe you could do an actual test using your power meter and this solution. But anyway, it’s not the perfect solution but for me as some how “technical fixated and interested” it does the work and helps me stay motivated. 🙂… Read more »
Thank you! 🙂 I can definitely see how it would be more accurate with some historical files to kind of shape the curve. It may be close enough for someone who has a power meter outside, but can’t afford or doesn’t want one inside.
The “same cadence = same watts” regardless of resistance does not seem to be true on my Scwinn IC 8. The resistance control is magnetic. When I increase the resistance and pedal at the same RPM , my power on Zwift goes up. If i crank the resistance way up, which reduces my RPM ‘cause its hard to pedal, my power on Zwift goes up. Perhaps the magnetic resistance makes the power output more accurate?
This seems right to me.
Thanks for commenting. The article was specifically about Zwift’s zPower calculation, which takes your wheel speed against a measured trainer resistance when someone only has speed and cadence sensors and no power. I believe Schwinn does a similar calculation but since it’s their bike they take resistance into account. It’s still a guess, but a potentially more accurate guess than speed on a fixed gear alone.
I’ve been using a Schwinn IC4 for 4 to 5 months and I improved over that time and its been great, BUT I went from D to upper B and I started thinking too much improvement in FTP and watts. So I just got some Assoima pedals and I’m back to earth. I was pushing 300-330 watts with the bike and now with the same resistance the pedals are telling me 200-230 watts. Time to reset my FTP and get down graded on Zwiftpower…
I setup my dumb Schwinn Evolution with speed/cadence. I was unhappy with the unspecified trainer setup so I chose a nashbar dumb trainer setting. At least now I can keep up with the rest of the some of zwift crowd. But riders are constantly blasting past me and thats ok. But if what you say is true noone could keep up with me at 90rpm. My cadence is usually around 80rpm and I’m 142kgs. watts ~230ish. I’m sure my z power is skewed due to my weight. I’d probably crush power meters. like everything else the estimations wouldn’t apply.
It is true, you can see the results of the test above, zPower on a spin bike is WAY above a normal power meter and has no correlation. It also depends on the size of the wheel you chose in Zwift and the size of the wheel on the spin bike as to where the watts fall in relation to RPM. The simple fact is ride and have fun with it, but it’s no real indication of your fitness or the power being produced, zPower can’t calculate that for a spin bike, it doesn’t know the resistance and you are… Read more »
I set up my Sunny stationary bike with speed and cadence on Zwift. I’ve read and re-read your article, and conclusions regarding its inaccuracy. I commute on a fixed gear, so riding without gear changes suits me fine. For the first couple of months I was getting steady and consistent readings, they may not have been accurate, but they were reliable for my exercise and enjoyment of zwift. I would race in D and C category and consistently come in last, so I definitely was not benefitting from an unfair advantage. More recently i’ve been noticing some crazy swings in… Read more »
My suggestion on your last sentence is to find some Assioma pedals, which are about $500. Simply put, zPower via speed and cadence doesn’t work on a spin bike and was never intended for a spin bike. zPower looks just at the speed sensor data and uses the known resistance curve from the trainer to calculate power. On a fixed gear spin bike (and on your fixed commuter) speed is always going to be directly tied to cadence, not resistance. The Wahoo speed and cadence sensors are about $100, Assioma pedals are about $500. People spend so much money trying… Read more »
Thanks for the reply, and point taken. Perhaps for next winter that will be the solution, though will have to invest in some cheap road shoes as well to pair with the Assioma pedals (investment is a bit more than the $100 for sensors, but maybe also manageable). For the time being, and while the weather is still uncertain for another month or so, I was hoping for some insight as to why I might be getting these crazy readings. As mentioned in your article, finding a resistance setting should manage to get readings that are reflective of effort, even… Read more »
Really the only thing that could be causing that are inconsistent speed readings from the sensor you have. Have you ever tried logging and charting the speed sensor data?
The speed sensor itself, not the speed shown in Zwift.
Good point, I haven’t.
I’ll hook it up to my fixie this weekend and see what happens.
Thanks Scott for the replies.
As Scott mentions get the Assiouma UNOs for accurate power. If you value Zwift it’s worth it. My wife’s setup, Peloton with UNOs. Opens up the door to Zwift and real power.
+1 for Assiuma’s. I put the UNO on my wife’s Peloton and now she can ride Zwift with very accurate power. If you already have a spin bike, and that’s your indoor setup, then upgrade it to REAL measured power with a setup that will a no brainer. I hear you on the other side, I’m a B rider now and there’s no going back that I know of. Unless you cancel your Zwift account and resign up with a new account.
Hi, great article! So, if I have a Star Trac bike that transmits power data via BLE, what would I need to complete my setup so that Zwift will pick up all of the date coming from the bike?