- 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.
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- Hey what's up guys,
This is Tariq here from smartbiketrainers.com .
Thanks for joining in.
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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.