How do the different turbos and software estimate power?

Anything about Power (watts)

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How do the different turbos and software estimate power?

Post by nickl » Fri Jan 08, 2010 8:40 pm

Hi, I posted this on the Fortius software forum as it fitted in with a thread, but I thought it might be more relevant here. I'm a bit puzzled by how the Fortius and TTS estimate power, if they do it differently, and if there are likely to be any differences due to the actual trainer (eg between a Flow upgraded with the i-magic upgrade, or an i-magic itself). Any input would be gratefully received!

Let me set the scene:

I have a Flow trainer with the i-magic upgrade. I have the latest version of the fortius software. A friend of mine came round to my house and did the 9.4km mountain time trial on the mallorca tour RLV. He hadn't ridden the course before and mistimed his effort and ended up with a time of 29.00, average power 211. Then he bought an i-magic, with the TTS software and 3 weeks later he did the same mountain time trial on the mallorca tour RLV. He was a little fitter and rode more sensibly, and did a time of 27.30. This time made sense, but his average power was actually lower, at 207. His weight was inputed as the same both times. I know there will be some differences between trainers, but I'd have thought that an average power of 207 for the same weight rider on the same course would result in a slower time than an average power of 211. This leads me to wonder how the trainer calculates power, and whether it calculates speed and power independently? I think it must, but can anyone confirm this?

When looking closely at his data from the rides, it's clear that as soon as the gradient becomes negative power on my friends trainer drops to unrealistically low levels, although his speeds remain realistic. This is noticeable on other rides he's done, where power immediately drops to unrealistically low levels as soon as the gradient becomes negative. Overall, it is not a huge problem, as speed remains reasonable so time of the ride is also reasonable. However I'm puzzled why his new i-magic with the new TTS software does this, while my 3 year old Flow with i-magic upgrade and fortius software does not. Any ideas?


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