Drafting question

[rstrom]

Hello,

I uploaded my ride that I did today and was asked if I drafting (I think it said 4.5%). At first I said yes (because I did a little bit of drafting, but not much - I would say less than 10%), but then I changed my mind and re-analyzed the route without the drafting. There was a 31w average difference and a 24w max wattage difference as well as a difference of about 330 calories.

The ride was a 55 mile ride with one other person and we didn't do a whole lot of drafting, a little bit, but more riding along side each other and a fair amount of hills (about 2850' elevation gain) so there was also a fair amount of rapid descending at some pretty decent speeds (peak 5 min = 31.5mph).

I'd appreciate it if someone would take a look at the ride file (if this can tell you anything) and/or give me some advice on what constitutes "drafting". Obviously if you're participating in a group ride and find yourself regularly tucked in the pack and saving some significant energy that would be drafting but I don't know that this ride qualifies. Lots of climbing by myself, descending by myself, with minimal drafting behind one person.

TIA,

Robert

[rstrom]

Well after thinking about this more (with a clearer head after a decent nights sleep) I feel a little dense (I think).

So is the iBike telling me that it thjinks that I drafted 4.5% of the time?

If that is correct and the iBikes calculations are correct in the amount of watts and calories that I saved by drafting 4.5% of the time on a 55 mile ride (2.475 miles), that is pretty significant.

Any clarification of this will be welcomed.

Thanks,

Robert

[mechgt]

From what I understand, the question is posed as this:

"Were you drafting? If yes, I'll keep the wind as is, if not (and this was an out an back sort of trip), then I'll adjust your wind such that it nets 0 wind over the duration of the ride."

So, depending on if you say yes or no, it'll either offset the wind setting the overall avg to 0, or leave it alone. At least that's the way I understand it.

[lorduintah]

In the current state of the auto-route, the algorithm attempts to do the best at analyzing the ride data. Some portion of a ride may appear to be different in an out and back if the wind is a little different in one direction than the other and can interpret this as possible drafting. If that is not the case - say due to oblique vectors of the wind, gusts and the like, then just answer no to the drafting. If you really did draft - then answer yes.

I suspect that as more is done along these lines, the algorithm will improve and we end up with an improved calibration of the profile on top of all other features that keep getting better with the iBike and analysis software.

Tom

[mechgt]

So, if like in OPs original situation, you drafted 'just a teensy bit'... I wonder what the best answer to the question is? Seems like I have this scenario a lot as well and I'm quite often on the fence as to what to answer. I suppose that 4% drafting equates to 'just a teensy bit', thus it'd be appropriate to answer 'yes, I drafted during this ride.'

[Velocomp]

I always pay a bit of attention to the wind.

A sufficiently strong tail wind can cause the drafting box to appear.

If you say "No" then there is no change to your wind data.

[rstrom]

Thanks for all the replies!!

I certainly understand the easy to answer "Did you draft question" and I definitely pay attention to the wind wind on each ride, etc.

I guess the main remaining question (kind of) is if I drafted a little bit on the ride as stated in my second post (reply to myself) and the iBike program comes up with "Drafting detected 4.5%" (or whatever percentage) do this indeed mean that it thinks that I drafted 4.5% of the time?

If so, then that was probably reasonable for this ride and that I should go ahead and accept it's assumption that I did draft.

BTW I did revert back to the lower wattage / yes I did draft numbers.

TIA,

Robert

[Velocomp]

Here's how it works:

1) The software compares wind speed to bike speed at each point of the ride

2) From our experience at looking at hundreds of group ride files, we know that whenever bike speed is above 15 mph and whenever wind speed is 65% or less than bike speed, then the rider is drafting.

3) The SW measures the percentage of the ride where condition 2) is met. This is where the % number comes from.

The reason for the "Did you Draft" question is because a strong tailwind can also trigger 2).

When "Yes" is answered the iBike leaves the wind data unaltered. When "No" is answered the SW applies appropriate corrections. For example, if it is an out-and-back ride and there is no drafting, the SW will make average wind speed equal average bike speed.

[rstrom]

John,

Thanks very much for the detailed clarification!!

Robert