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Same timing, course but different Power?

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over 3 years ago

Dear all,
Relatively new to the Tacx and really enjoying it! However I had a situation occur that I don't understand, or my physics is rusty.

I've been riding the canned Gascony course, and a few months ago and yesterday I did a rides that were just 1 second apart in timing. Hence the speed and distance indicated were the same. However watt output was 20W difference, with the higher wattage ride def being more effort (after a few more months of training).

My question is - for the same course and speed, should I be expecting power output levels to be conserved (the same) in both scenarios? If yes, is there an issue with the Neo's power measurement?

If Power isn't conserved, could someone explain why it shouldn't be so, since Power = Work Done / Time and (I think the work done quantity and time are the same)? 

Much appreciated for any suggestions, thanks!

Best,
Jason

  • 0 over 3 years ago

    I don't use the Tacx software and I don't know the course, but a quick search suggests that it's a bumpy one. This means that there is a strategy to using power wisely.

    You can save more seconds by riding harder up the inclines and easing off for recovery on descents than riding with steady power (e.g. in erg mode) for all gradients. So while your average power might differ by 20W the outcome in time/speed is not cut and dried on a lumpy course. Extra power on descents does not add as much value to the performance as extra power on the ascents, so the final result depends on your pacing strategy, not simply your average power.

    This is all down to the effects of drag. The faster you go the more power it takes to increase speed further, so trying to save a few seconds on a decent with more power will be less effective than increasing your power when climbing and not seeing much change in drag.

    If you use a tool such as Bestbikesplit you can generate a pacing strategy for a course. You will observe that the optimum strategy is more power when climbing, less when descending. If you do something different you will be wasting effort in a less effective fashion.

    https://youtu.be/-NwHNUhopIQ

  • 0 over 3 years ago in reply to eezytiger

    Thanks much, that makes sense to me!