Oh, Garmin, you rascal!

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Jthanmyfitnesspal
Jthanmyfitnesspal Posts: 3,521 Member
in Fitness and Exercise
TL/DR: The cycling calorie estimates of Garmin are higher when I don't monitor heart rate. I think that's ridiculous!

After a very difficult winter and spring (COVID and a big house move), I'm finally starting back up with outdoor cycling (among other things). I have a Garmin bicycle computer (Edge 530) and a Garmin watch (Fenix S6). Yes, they're pretty redundant. I only got the bike computer because 1) needed a larger screen, 2) to pair with the back-looking radar, and 3) for "incident detection." For a long time, I had a chest HRM that I wore when cycling, but it died. Since then I've sometimes successfully gotten the bike computer to read the HRM from the watch. (Yes, it can do that!) But, you have to put the watch in transmit mode before starting your ride or it doesn't work. So, I've done the same ride with and without HR data.

I can report that I get a higher calorie estimate WITHOUT the HR data! That seems ridiculous to me, as the energy required should be estimated from your bodyweight, speed, and grade. Who cares what your HR was!? Maybe I'm missing some other variable that's changing these estimates.

PS I really don't want to $pring for a power meter-- my power is way to low to worry about it. I just need a ball-park calorie estimate.

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  • NorthCascades
    NorthCascades Posts: 10,970 Member
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    If you want a ballpark calorie estimate, you have to suffer give it something to estimate from (gigo) or accept what it gives you based on not really having any information.

    Speed isn't really a meaningful thing for outdoor cycling except in controlled circumstances because wind, traffic, and other factors have such a large effect. This isn't like running, you have wheels and you can coast.
  • NorthCascades
    NorthCascades Posts: 10,970 Member
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    PS - you can pair the watch to tie Varia and it will vibrate noticably on your wrist when there's traffic behind you. I find it works very well in practice.
  • sijomial
    sijomial Posts: 19,811 Member
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    But you are getting two ballpark estimates!
    Pick one?

    Both of those ballpark estimates will be missing useful information whichever method you pick - it's hot so your HR goes up (or you have had an espresso or a near miss....), headwind, baggy jacket or flat tyre that Garmin doesn't know about....

    My own HR to power relationship doesn't seem to be particularly linear. I can produce "moderate" power at very low HR but when I push to my "good" power output it takes relatively a lot higher pulse.

    Power meters really aren't that expensive anymore and they are a brilliant training tool irrespective of your current power output.

    I didn't have a great experience with Garmin chest straps but my Wahoo TICKR has been spot on over hundreds of hours.

  • NorthCascades
    NorthCascades Posts: 10,970 Member
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    Jthanmyfitnesspal wrote: »
    I can report that I get a higher calorie estimate WITHOUT the HR data! That seems ridiculous to me, as the energy required should be estimated from your bodyweight, speed, and grade. Who cares what your HR was!? Maybe I'm missing some other variable that's changing these estimates.

    Your intuition is right, but the devil is always in the details.

    The energy balance equation for cycling is basically speed = power (energy use) vs all opposing forces. You mentioned grade, or gravity; on a road bike the biggest one is often air resistance. The energy it takes to cut through the air goes down by up to 1/3 when you draft somebody. It goes up with a head wind and baggy clothes, down with a tail wind and deep wheels.

    Tires make a much larger difference than you would think. Gatorskins vs Pro Ones are a difference of about 100 kCal per hour at the same speed.

    Grade: This comes from GPS, or baro on units that have one, combined with a digital elevation model which has medium resolution. All of this has a large margin of error, that's why it's delayed and smoothed on your head unit. Sometimes the DEM doesn't know about a bridge and thinks you went to the bottom of a chasm and back up. Sometimes the barometer thinks you've been riding up hill all day because the weather is changing.

    Your Garmin doesn't know what the wind is doing, if you're riding solo or in somebody's slipstream, or what tires you're using, and only has a vague idea about grade.

    The reason heart rates get you closer to the truth is because now it has more information to work with and an idea of your internal workload.
  • Jthanmyfitnesspal
    Jthanmyfitnesspal Posts: 3,521 Member
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    @sijomial : Which one would you recommend? I think the single-pedal Look-style ones are now under $500, but I don't like that style of cleat and don't have the shoes. Also, the pedal ones can't be as accurate as the crank-based ones as they don't exactly measure torque, so there's some correction applied.

    I had a Tickr, which worked brilliantly for at least 5 years. It's finally dead. :'( Tragically, I replaced it with the Garmin Swim HRM, which truly sucks, even for swimming. (It works by having a waterproof band over the electrodes and it has to be worn very tight. I still got crazy readings. I think the watch is more accurate.) Anyway, when I remember to turn the HR transmit on, the watch/bike computer work well.
  • NorthCascades
    NorthCascades Posts: 10,970 Member
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    Here's a used PowerTap wheel for $120.

    https://www.ebay.com/itm/374060201843?mkevt=1&mkcid=1&mkrid=711-53200-19255-0&campid=5338678874&toolid=20006&customid=s%3AGS%3Bgc%3Af5b47147981a145c5ebd13e29f010d25%3Bpt%3A1%3Bchoc%3A1&customid=s:GS;gc:f5b47147981a145c5ebd13e29f010d25;pt:1;choc:2&msclkid=f5b47147981a145c5ebd13e29f010d25
  • sijomial
    sijomial Posts: 19,811 Member
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    Jthanmyfitnesspal wrote: »
    @sijomial : Which one would you recommend? I think the single-pedal Look-style ones are now under $500, but I don't like that style of cleat and don't have the shoes. Also, the pedal ones can't be as accurate as the crank-based ones as they don't exactly measure torque, so there's some correction applied.

    I had a Tickr, which worked brilliantly for at least 5 years. It's finally dead. :'( Tragically, I replaced it with the Garmin Swim HRM, which truly sucks, even for swimming. (It works by having a waterproof band over the electrodes and it has to be worn very tight. I still got crazy readings. I think the watch is more accurate.) Anyway, when I remember to turn the HR transmit on, the watch/bike computer work well.

    It's such a tiny difference between crank and pedal based technology I would focus on price and convenience, strain gauges have been around for an age.
    I went with Favero Assioma single sided - they now do Shimano cleat fittings as well as the Lifeline/Keo Look ones that I use.
    My biggest reason for buying pedal mounted not crank was the ability to fit it to different bikes, it's been used on three of my own bikes so far and even a rental when away. That's about 17,000 miles in the last four years so the initial cost is spread pretty thin by now.
    (It could also be fitted to an indoor training set up of course.)
  • NorthCascades
    NorthCascades Posts: 10,970 Member
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    https://4iiii.com/usa/products/pdp/clearance-left-side-precision-powermeter-ride-ready/shimano-ultegra-fc-6800-172-5mm-previously-ridden/

    $240 for a used, left crank arm power meter.

    I personally wouldn't go with a lefty, but lots of people have them and use them to benefit their training and for other purposes. My hesitation is that your Garmin will just double the power coming out of your left leg, which is probably close enough for practical purposes, but obviously imprecise. I don't need the L/R balance and almost nobody does, but I want total power to be as close as possible. For what it's worth I measure both legs separately and I have a small imbalance at low speeds on flat ground but as soon as I put any effort out it goes right to 50/50.

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