Powertap SL+ Power Display smoothing feature

[RBaker2778]

Hello All,

I have been trying to figure out my powertap SL+. It has a feature that lets you delay the power refresh rate on the display so your watts don't jump around so much. I have found the configure device section on the software, made the change, and updated it. Nevertheless, it still jumps around, no matter what display rate I set it to. Anyone else run into this?

[djg21]

Hello All,

I have been trying to figure out my powertap SL+. It has a feature that lets you delay the power refresh rate on the display so your watts don't jump around so much. I have found the configure device section on the software, made the change, and updated it. Nevertheless, it still jumps around, no matter what display rate I set it to. Anyone else run into this?

My understanding is that power output fluctuates at various points during the pedal stroke, and that as a result, it tends to jump around. I seem to recall that Coggins references this in his book Training With A Power Meter. I think he uses the term "eschatic" to describe power output, by which he means that is prone to fluctuations. (I can't access the book without waking my wife, so I'm not sure if I have the correct word).

I set my display to average power for at 3 secs. It still jumped around a fair amount. My recollection is that you can set the display to average at 5 sec periods too.

I now use a Garmin Edge rather than the powertap CPU, and when doing intervals, I focus more on average power than actual power. I know the range I should be in, pick a number on the high side of that range, and try to keep my average output during the interval from falling below that number. I use the lap timing function to do this. You should be able to do the same thing with the Powertap CPU.

[rinconryder]

I agree with above. I used power for two plus years in training for triathlon. If you are looking at your numbers that much, it is going to drive you crazy. 10-15 watt fluctuations within seconds is pretty standard. I mainly used it as a baseline to keep myself honest and didn't let myself drop below a certain number.

Power can be a great tool if you use it right - but it can be nothing but an expensive toy if you don't keep track of data.

Things that I would look at after a ride:

1. avg. watts
2. Total work: really helps you eat the proper amount
3. power vs. HR - HR is still important, but the more you use power you can then guestimate pretty closely what the other will be based on one number alone, unless you are either sick or overtrained, which is very useful to know!

[runtimmyc]

I have found the configure device section on the software, made the change, and updated it.

You have to change it on the powertap computer head, or garmin or whatever. Changing it in the software on your laptop won't change the display when you are riding.

[bocarider]

It’s going to jump around no matter what when you are riding due to the constantly changing state of power output when you are riding (Coggins and Allen have a word for it that I cannot remember at the moment and my Training with a Power Meter Book is at home). Wind resistance, rolling resistance from the road surface, cadence, gear shifting all contribute to the irregularity of power output. Plus, with sampling every few seconds, depending on how you have your computer set up, the readout is going to be all over the place.

Using the interval function on the Powertap head is one way to get a sense of what you are averaging over a given period of time, which is a more meaningful piece of data. If you set the watts line to average power and then mark an interval (push both buttons at the same time – a "1" will appear in the lower left part of the screen and then increase each time you mark an interval) you can then see your average watt output until you mark another interval. For example, if you are doing 20 minute steady state intervals, you can see, in real time, what your average watts are for each 20 minute interval. If you get a Garmin 705 you can set multiple data fields to see average, real time and max power if you a total geek like I am about this stuff.

Note that if you download the data into WKO+ there are a couple of functions that modify the data to give you what Coggins and Allen call "normalized" power which takes into account turns, slowing down and speeding up out of turns and other factors that contribute to the irregular nature of power output when riding. That number tends to run a little higher than the raw average that shows up for a particular interval.

[djg21]

It’s going to jump around no matter what when you are riding due to the constantly changing state of power output when you are riding (Coggins and Allen have a word for it that I cannot remember at the moment and my Training with a Power Meter Book is at home). Wind resistance, rolling resistance from the road surface, cadence, gear shifting all contribute to the irregularity of power output. Plus, with sampling every few seconds, depending on how you have your computer set up, the readout is going to be all over the place.

Using the interval function on the Powertap head is one way to get a sense of what you are averaging over a given period of time, which is a more meaningful piece of data. If you set the watts line to average power and then mark an interval (push both buttons at the same time – a "1" will appear in the lower left part of the screen and then increase each time you mark an interval) you can then see your average watt output until you mark another interval. For example, if you are doing 20 minute steady state intervals, you can see, in real time, what your average watts are for each 20 minute interval. If you get a Garmin 705 you can set multiple data fields to see average, real time and max power if you a total geek like I am about this stuff.

Note that if you download the data into WKO+ there are a couple of functions that modify the data to give you what Coggins and Allen call "normalized" power which takes into account turns, slowing down and speeding up out of turns and other factors that contribute to the irregular nature of power output when riding. That number tends to run a little higher than the raw average that shows up for a particular interval.


The powertap samples every second irrespective of how the display is set. The averaging just controls what is displayed on the CPU.

As an aside, I hate the Powertap CPU, as I like to be able to see HR, current power, average power, speed, cadence, and lap time while doing intervals. I used to keep the Powertap CPU on my stem displaying average or instantaneous power, HR and ride time, and a second cycling computer on the bars set to display stopwatch and speed. I have replaced both of these with the edge, which gives me far more information and has a very customizable display. I'd be afraid to use the Garmin in a criterium, and likely will use just the Powertap CPU. But for training, the Edge is awesome.

[bocarider]

Yeah - l love my Edge 705 - it works really well for me.