ERG MODE: Does FLYWHEEL Speed AFFECT Power Accuracy?
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– In this video, I wanna
talk about gear selection and it’s affect on power accuracy. Is a trainer, more accurate
in the small chain ring than the big chain ring or vice versa. In other words, how does
flywheel speed affect power accuracy. Does it even matter? In the past few weeks
I did a lot of riding and I crunched through a lot of data from two different trainers, three different power meters, and two different bikes, and I did the same workout six times. That’s over six hours of riding. And hopefully I can answer
this question or maybe not. But let’s dig into it, or I probably should say let’s try to dig myself
out of that rabbit hole. (bouncy lounge music) – Hey what’s up guys, This is Tariq here from
smartbiketrainers.com . Thanks for joining in. If this is your first time here, this is where I talk about
smart trainers and fitness tech, and if you want to learn
more about indoor training and smart trainers, and see more content like this, hit that subscribe button. And if you find this video
helpful I would appreciate it if you hit the like button and tell your friends about this video, and share it on Facebook,
Twitter and uh, everywhere. So some chatter’s out
there on social media and different forums that the
trainer measurement might be more accurate in a smaller chain ring than the big chain ring. Basically your smart trainer
is much better at calculating power at low flywheel speed in ERG Mode, than a flywheel- than
a fast flywheel speed. Let me explain. Now probably the reason for
this is we did have some trainers this year from certain
companies report different power at different flywheel speed. And one of them happened
to be the Tacx Neo, or Tacx Neo 2, and the Tacx Neo has that
reputation for being the most accurate or one of the most
accurate trainers in the market. So when you are riding
on your smart trainer and have your bike in a smaller gear, like a small chain ring in the front, and the middle to bigger cog in the rear, the flywheel isn’t going
to be spinning as fast and the trainer will have
an easier time adjusting resistance in ERG Mode to
keep you at your target watts, and you’re gonna see smoother lines. Also that’s why many riders
complain and wonder why their average speed is so much
slower indoors in ERG Mode, but that’s a different topic. However if you use a bigger gear, the flywheel will spin a lot
faster and the trainer will have a harder time adjusting resistance, and because of that, you will see more fluctuations
in power like you see in this chart right here. Now power lines might not
be as smooth in the big ring as in the smaller gear, but this is not what
I’m talking about here. I am more concerned about power accuracy. And I talked about ERG Mode
and the differences between a small and a bigger ring
in a little more details in this video right here. You can go and watch that
one after you finish watching this video, if you feel like binge
watching ERG Mode stuff today instead of The Office or
Netflix or any other show, and I will link to that video
in the description below. So I ran a bunch of tests, and the main one I did was
a three by ten minutes, and I wanted to look at power
averages and I wanted to collect data from longer intervals, and use three different
gearing combinations. Power fluctuates and different
power meters measure power at different points, so I wanted to have a larger
data sample to better measure the effect of flywheel
speed on power measurement. Hopefully that makes sense. So I ran the tests on the Neo
2 and Wahoo Kickr 2018 model. The power meters I used,
Power2Max on my tri-bike, and I also have another
Power2Max power meter on my road bike. The Assioma pedals Duo that I
switch between the two bikes. And to set a base line,
here’s a ride I did. This is just a regular
ride using all three of my power meters so as you
see they were very close. The Assioma was a bit higher
which was expected because it’s a pedal-based power meter, and pedal-based power
meters usually measure power closer to the source. And the averages for this
ride were 180 for the Neo, 181 for Power2Max and 183 for Assioma. So on the Kickr I did the first
ten minutes in a small gear. The Kickr average
flywheel speed was around thirteen miles per hour. The second interval flywheel speed, average 19 miles per hour
and the third interval in a big gear, average flywheel speed 29 miles per hour. And when comparing the power
measurement between all three, my Power2Max across all
three intervals was off by only 0.41 percent. So that’s really close and based on that, we can say the flywheel
speed or gear selection had no effect on power accuracy. But let’s keep going. The Assioma was a different story. Even it though it was calibrated
however it was measuring between three to four and
a half percent higher, so we’re talking about
eight to eleven watts higher for a ten minute interval. Let’s take a look at the Neo 2. My Power2Max was consistent
throughout all my rides. In a small gear or the
lowest flywheel speed, it was reading a bit low. We’re talking about one and
a half to three percent lower across all three different workouts. The second interval in a- in the big ring, the flywheel was reporting
a speed of around 20 miles per hour, and power measurement was spot on. Then at a higher flywheel speed
it was a little bit higher, but not much higher. We’re talking about three watts
higher and was even spot on on the third ride I did. The Assioma however was
reading a bit differently. It was spot on in the small
ring but measured a little bit higher at a higher speed or
the- went up in a bigger gear. But it was still within acceptable range. But then up to five percent
higher when going to a very big gear and the flywheel
speed was running around 27, 29 miles per hour. So looking at all three rides, I think we can say flywheel
speed did not have, did not really have an
effect on power accuracy when comparing it to my
crank-based power meter. However when looking
at the Assioma pedals, you might arrive at a
different conclusion. Now according to Favero, their pedals have
instantaneous power system, or as they call it, instantaneous angular velocity or IAV. Meaning their pedals measure
power instantaneously throughout the pedal stroke, where other power meters
calculate power using the average angular velocity per rotation. And according Favero, this might introduce an additional error up to
four and a half percent compared to instantaneous
power calcualation. If that is the case then that
might explain why the Assioma might measure a little bit
higher or different than a smart trainer or even
different power meter in some situations. If you have an Assioma Duo
let me know if you notice the same trend. If you wanna run the same workout I did, I will link to it down below, and I will have it on
smartbiketrainers.com as well. So here are my takeaways. As long as you have a good trainer, meaning it’s not a defect
and calibrated correctly, it shouldn’t really matter
which gear you select. Power measurement should
remain consistent regardless of your flywheel speed. When in ERG Mode the general
rule is to stay at a low gear for a more responsive trainer, whether you like the big chain
ring or the small chain ring, shift to the middle of the cassette and keep your chain straight. This will also give you a quieter trainer, and minimize the stress on your
chain and that will give you the closest power measurement
to your power meter regardless if you use a
crank-based or a pedal-based power meter. Find a gearing combination
that feels more natural to you and use that gearing combination. Stay away from uncommon
gearing combination like a really big gear
or a really small gear like I did for this test, unless of course there
is a floor wattage issue. Some trainers might have
mechanical limitation that might prevent you from hitting
your target whilst you’re in recovery intervals. In that case switch to a smaller gear. Okay. Hope you find this video helpful. If you did, hit that like
button and subscribe. That’s all I have, thanks for watching and see you in the next video.

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