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Bike mass + tire structure in computer

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Bike mass + tire structure in computer

Old 05-05-20, 03:36 AM
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Sergio_CH
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Bike mass + tire structure in computer

I had two rear punctures two days in a row riding my road bike.
Reminded me of my uni days when I was riding my MTB daily to the uni (including winter snow and ice) and had to fix two punctures a day every day (due to fine gravel that was put on the roads for traction instead of salt).

I am not a happy bunny when I have to fix punctures (and on road bike that means replacing new tubes which are not cheap if they are light), therefore yesterday, instead of my road bike, I took my good ole Trek Elite 9.8 for a road ride.

I was going on that MTB with Racing Ralph knobbly tires and I was thinking - why do we not put the bike weight and tire structure information (=friction) into bike computers?
I am sure I spend much more energy sitting upright and riding a 12kg bike with wide knobblies then bent over pedalling an 8kg bike with skinny GP4000IIs rubber.

I guess this kind of information would be taken into account implicitly by a power meter, but what if you do not have a power meter?
Would changing one's body weight in the computer (Garmin in my case) to bodyweight + bikeweight inprove spent calories calculation?
Or are the differences negligible?

Another question - does anyone know MTB (26") road tires that are as puncture resistant as the standard MTB tires (or at least better than GS4000II) but do not weigh 500+ grams per tire?
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Old 05-05-20, 04:00 AM
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jpescatore
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The difference in calories burned as a function of weight is minimal on flat ground and small inclines, and for normal human beings a few pounds either way in bike weight is not even that big a factor on climbs - a 150 lb rider on a 25 lb bike is only 2% lighter than when that rider is on a 30 lb bike. So, instead of burning 40 Kcal/mile, you might be burning 41 calories per mile - a difference that is well under all the other factors that cause calorie burn to be different! Same with aero changes for most humans, ie non racers. As you mention power is better to monitor, if you don't have that heart rate is a proxy for it - better than weight, anyway.

I just checked - Garmin devices that allow you to enter weight use it for calorie calculation only if you are not using a heart rate monitor. Here's what Garmin says:

In the absence of a Heart Rate Monitor (HRM) or power meter, speed and elevation along with the user profile are the default values for calculating caloric burn. On the Edge 510 and Edge 810, you can input the weight value for each bike profile used and this is added to your weight in the user settings. On newer Edge products, a default bike weight value of twenty pounds is added. The difference of a few pounds to this value is incidental to the accuracy of the calorie burn calculation when using speed and elevation as the default data source. In order to achieve the most accurate caloric burn calculation, we recommend using an HRM or power meter and ensuring your user profile is accurate.

Last edited by jpescatore; 05-05-20 at 04:05 AM.
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Old 05-05-20, 05:26 AM
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Sergio_CH
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Yes, you are right, I forgot about Garmin's algo for calorie computation, they use HR when the belt is on (I always have it on) or move to a more advanced computation when there is a power meter connected.
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