funkiestj wrote: ↑Sat Nov 10, 2018 11:58 pm
Is there an FAQ for new Powerpod users (i.e. us folk who have one now and have used it for a few rides)? E.g. these might be n00b FAQs:
- How does PowerPod (and Isaac) handle the rider (me) changing riding position (hoods to the drops, vice versa)?
- can I do an out and back calibration ride on a climb/decent?
- where can I find a nice "out front" handlebar gopro mount (gopro only, not a gopro+garmin combo)? Presumably this should be aluminum rather than plastic for rigidity reasons? I've seen some on the internet but it is hard to know which one to get.
- in the 'device mount location' setting, what constitutes 'front mount'? Would that be my desired handle bar mount that sticks out front a bit?
there must be other questions.
Since we haven't been asked most of the above questions before, they don't qualify as "FAQ"
However, we are delighted to answer them:
1) Yes, there is an FAQ for PowerPod. It is our "Tips and Troubleshooting" Guide, available here (and, I believe, included with your PP)
https://velocomp.com/support/
2) When you set up PowerPod, you specify your "normal" ride position: hoods, drops, or TT. Your normal ride position is the one you ride in most frequently.
Obviously, PP cannot "know" when you change ride position, so when you do move momentarily, say, from hoods to the drops,
then in the drops section of the ride only, your PP watts could somewhat high (because PP will think you are still in the somewhat less aerodynamic hoods position).
The question is: what is the "error" in watts caused by changing ride position away from your "normal" position? Good question, but there is no easy way to answer it!
A. Moving from hoods to drops does reduce CdA, but the AMOUNT of CdA reduction varies from person to person, and bike to bike. One example: for me and my bike setup, my CdA in the drops not even 1% lower than my CdA on the hoods (I've measured my CdA in both positions with AeroPod). So in my case, there is no discernible "error" in PowerPod readings when I move from hoods to drops.
B. For other riders, we've seen reports that their "drops CdA" can be as much as 5% lower than their "hoods CdA". Does that mean that PowerPod would be "wrong" by 5% when that rider moves from hoods to drops? IT ISN"T THAT SIMPLE:
C.
The watts reported by PowerPod depends on why you are producing them. PowerPod adds up "hill" watts, "acceleration" watts, "friction" watts, and "aero" watts and reports their sum as "total watts" (the watts you see on your bike computer screen).
Let's suppose you're riding on the hoods and PowerPod reports you're producing 200W. Then you move to the drops, your CdA drops by 5%, but your PowerPod still reports you are producing 200W. By how much is PowerPod over-reporting? It depends...
1. If you are ascending a 5% grade, riding in the drops produces a (theoretical) PP watts "error" of 1.5%--3W
2. If you are on the flats at a constant speed, riding in the drops produces a (theoretical) PP watts error of 4%--6W. Why is it not 5%?
Because some of your watts are overcoming friction, which is not dependent on ride position.
3. As you can easily imagine, if your ride has hills, flat spots, descents (this is the most likely situation), then the "composite" error of riding
while the drops, is probably somewhere between 1% and 4%.
C. Another factor is this:
most people ride in the same position most of the time. So, if you're doing a long interval on the flats (where the potential for ride position watts error is the maximum), and you ride 60% on the hoods (your "normal" position) and 40% on the drops, the watts "error" for the entire section will be around 40% * 4% = 1.6%!! Even for riders who do power training, this is perfectly acceptable.
D. The ONE PLACE where PowerPod
can get "into trouble" is on fast descents, where riders go into aero tucks (basically from hoods to TT, an extreme change of CdA, as much as 30%). Now, most riders don't pedal on fast descents (it is a waste of energy--the hill is doing all the work!), and when cadence = 0 then power = 0--PowerPod is reporting the right number, irrespective of ride position. BUT, if the rider soft pedals during the fast descent, then cadence is not zero, and then PowerPod likely will significantly over-report watts. Fortunately these sections are easy to spot in the ride file and to edit out in Isaac. The edited ride file can then be exported to Training Peaks, etc.
Arm-chair physicists love to bash the opposing force technology approach, and ride position change is the battering ram they use to pound away. But in the real world, for most cyclists, it is not a big deal.
3) Yes, you can do an O&B on an ascent/descent. The only "trick" to be aware of is that, if on the out-portion of your calibration your hill is steep, when you reach the 50W mark, you'll need to STOP immediately and turn around. PP will not show solid red at the 50W mark, because it uses low speed to determine when you've turned around.
4) Depending on your handlebars, you can use our AeroPod under-the-bars TT mount. Or, if you have round handlebars, we
may have some other suggestions. Please email
technicalsupport@velocomp.com with your question, and Tom will get back to you.
5) Yes, if your PP mount location is in the front of the bike, then that would be a front mount. GOOD NEWS: when you do the out-and-back calibration, the calibration will AUTOMATICALLY figure out your actual PP location,
no matter what you selected during setup.