Power Meter Temperature Drift, Or Sharp Decline In Fitness?
spredy
Posts: 48
Hey,
After recently purchasing a Power2Max power meter I did what most people seem to do and did a test to set my zones. Despite it being late October, the temperature while doing the test averaged 17 degrees celsius. I warmed up, rode out of the city and did the 20 minute test on a quiet stretch of road, and rode back. Upon arriving home I found I'd averaged 306 watts for the 20 minutes and had a 1 hour NP of 277 for the whole ride. I weigh around 66kg so was pretty pleased.
Over the next week I trained using the levels set by the test, and what the numbers suggested was a hard effort felt hard, but still obtainable, and the easy efforts felt just that, easy. However, as the temperature started to decline, what the numbers suggested should be a hard effort now seemed impossible. A few weeks later when doing a reasonably well rested 20 minute all out effort in 6 degree weather I, according to the power meter could only muster 255 watts, even though it felt like all I had at the time.
I had read that Power2Max devices used to under-report watts in cold weather, however this has supposedly been addressed. Could my device have a defect, could my fitness really have declined that quickly, or as a skinny person, could the cold be really getting to me that much?
I've not seen a great deal on how the cold can alter performance, but I'm wrapping up well, so I wouldn't think I'd see such huge drops in power. I appreciate we can probably only speculate, but I thought I'd ask here instead of just speculating on my own, haha.
Thanks, Ed.
After recently purchasing a Power2Max power meter I did what most people seem to do and did a test to set my zones. Despite it being late October, the temperature while doing the test averaged 17 degrees celsius. I warmed up, rode out of the city and did the 20 minute test on a quiet stretch of road, and rode back. Upon arriving home I found I'd averaged 306 watts for the 20 minutes and had a 1 hour NP of 277 for the whole ride. I weigh around 66kg so was pretty pleased.
Over the next week I trained using the levels set by the test, and what the numbers suggested was a hard effort felt hard, but still obtainable, and the easy efforts felt just that, easy. However, as the temperature started to decline, what the numbers suggested should be a hard effort now seemed impossible. A few weeks later when doing a reasonably well rested 20 minute all out effort in 6 degree weather I, according to the power meter could only muster 255 watts, even though it felt like all I had at the time.
I had read that Power2Max devices used to under-report watts in cold weather, however this has supposedly been addressed. Could my device have a defect, could my fitness really have declined that quickly, or as a skinny person, could the cold be really getting to me that much?
I've not seen a great deal on how the cold can alter performance, but I'm wrapping up well, so I wouldn't think I'd see such huge drops in power. I appreciate we can probably only speculate, but I thought I'd ask here instead of just speculating on my own, haha.
Thanks, Ed.
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Comments
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A few thoughts:
1) If you are now wrapped up warm, does that include your legs? Any full leg covering will take effort to move and stretch, so some power (I have no valid numbers for how much, but I suspect not very much) will be "lost" due to the extra clothing.
2) "New toy" syndrome. We are now in the realm of speculation, but could it be that when you first got the power meter you were trying harder simply because you now had a power meter? The effect of psychology on what a person considers to be their maximum effort is well documented - you really can go faster just by believing you can go faster. There was a TV programme I saw a couple of years ago where they were working with track cyclists. They gave half the cyclists plain water, and half were given plain water with just food colouring added, but the cyclists were told that this was a new wonder performance-enhancing substance. More than half the cyclists given the "wonder substance" put in new PBs. No physiological change - just a mental one.
3) Are you now more mentally tired than you were before? Odd as it sounds, if you spend all day working the brain, the body doesn't do as well physically. The military now include the relationship between mental fatigue and physical performance in their training. Have a listen to http://www.bbc.co.uk/programmes/p01nwhsx. The relevant bit starts at 1:10.0 -
Yeah, they're reasonably well wrapped up, a pair of my summer tights under some winter tights which have fleece on the inside and panelling on the outside to keep the wind out, as well as some over shoes to help keep my feet toasty.
You make some good points on the mental side of things, especially as it was the first test, I didn't go into it with any expectations of what I could put out, or the relationship between watts and perceived effort. Maybe in subsequent ones I've been psyching myself out, and that coupled with the weather? Still though, a decline in power of at least !0% is quite substantial, and disheartening.0 -
Can you not use a turbo ? You really need to keep conditions as close as possible to compare sessions.
If one session is odd - wait and try again. I miscalibrated my powermeter one time and it gave lower readings but it was fine the next time.0 -
You know I've been thinking the same about my power2max as well..some days it seems really hard to achieve wattage that I normally find easy...training as I have done all year...and the only diff really has been the temp.
I've been meaning to borrow my friends powertap and compare for a week.0 -
How old or new is your Power2Max? They released a newer version a while ago which has in-built temperature compensation.
You just stop pedalling for a few seconds and it automatically recalibrates... do you ever do that during your training sessions?
There have been a few times when I've taken the bike from the warm indoors to the relatively cold, and the power readings were way off... a few seconds of freewheeling sorted it immediately though. I bought mine at the beginning of the year.0 -
I've been running my P2M for a year now, and only these past few weeks have I noticed any odd numbers / drift. I guess I'm now experienced enough to notice, whereas before I was riding and thought, 'hey, they're great numbers etc etc', and not understand what was happening.
I've read up alot on how the meters work and how the cold can effect them, and if I'm correct in my understanding, temp drift can account can explain quite alot of the oddities in my power traces because of the way I ride.
As my rides at the moment are constant power from the off, on my favoured training route I don't freewheel until I hit the first junction, about 20mins into my ride. Assuming the temp compensation only happens when you freewheel (and it's not constantly working in the background), there will be a big difference in temp between when my bike left the house - 16-20degrees - an say 3-4 degrees outside. I'm sure I saw a shift of 30+watts the other day for the same heart rate.
Same thing happened on a turbo session a couple of weeks ago. No freewheeling during the session, and straight on bike as soon as I took it outside onto the patio. No wonder I coudldn't hit the numbers.
I've now started leaving the bike outside for 10-20mins prior to a ride to help it adjust to the outside temp so it shouldn't shift as much during the ride. Also during the ride I'm trying to get in the habit of freewheeling every 10-20mins or so, as there are a few micro climates here and the shift in temp does vary more than you'd expect.
Or as someone else said it could be that you're tired. It could be a one off result? Some days, you won't 'have it'. I find on colder days I suffer mentally, and that shows in my riding ability!0 -
It could be heart rate drift or just heart rate catching up with the effort as opposed to temp drift in the powermeter....could be both.
I had drift issues with p2max when the newer versions came out. The drift was very noticeable when training on rollers in a cold extension. Again very hard to tell how much was heart rate drift, oil in the rollers warming (if that would make any difference in resistance I don't know) but it was clear the power meter was poorly tracking power in comparison to similar rides on rotor power. Ditched the p2max in the end as I just couldn't rely on its figures.0 -
I live in the center of a city, I never just hit the road and go, I have to work my way out of town first, so there will be a lot of freewheeling in traffic and stuff. Or, I wait till I'm out of town to start recording, so after the 10-15 minutes it takes to get me there, it should be used to the cold. I bought mine in October, so it should have the temperature compensation of the newer models.
To what extent have you guys noticed drift? What kind of numbers were you regularly hitting, as opposed to when you thought drift could be at work?
In the warmer rides I was successfully doing ftp 20 minute intervals at around 280 watts, and having whole hour and a half long rides average around 250 watts. Once it gets to 5 degrees or so riding at 280 watts even for 20 minutes or so seems impossible. And one ride recently, I was killing myself to average even 210 watts right from the start.
My dad has a cheap indoor trainer I can hook the bike up to, so I may give that a go, and see if I notice a difference. However, if things go well, it'll be hard to differentiate whether it's the power meter or me who is benefitting from the warmth :L0 -
If you have doubts it might be worth trying some conscious freewheeling, wait for the cadence readout to go to 0.
But I expect all your numbers are 'correct' and that's just the way it is. Using an original but upgraded P2Max I ran a couple of time trials in April/May at over 290W, then could only manage 250W in a 20minute road effort in late November. I'm fitter now than I was then.
IME generally with a P2Max the speed and power correlate, I don't have the impression that the power numbers are erratic.
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It was easy to tell it was drifting on a trainer. If I recalibrated it (or zero offset...whatever it is) after 30mins or so then power would jump by about 20-30w for the same cadence at the same gear. I would do the offset as I could tell the watts were changing. If it was a long roller ride then it would noticably drift again. I can't remember for sure which way round it was- high or low...it was quite some time ago. It was the second version with the temperature correction but not the newest version. Maybe they've sorted it now. Anyway it seems that all power meter have at least one reoccuring issue all of which seem equally frustrating!0
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Mine is the older version with the temp correction. I've noticed it going from the house to the out doors, I can start off the ride hitting 260w with ease then 15 min later I'm finding it tough to put out 220w (which isn't even top even of power zone 2!) then another 15 min down the road my figures normalize.
I do 'zero offset' when going through town as I have to coast there...maybe I'll try after 20 min or so and see how I get on.
Sometimes it is legs but sometimes my HR is way out for the power as well which is what raises suspicions.
Probably doesn't help that my training bike lives next to the rad in the hallway!0 -
A couple of degrees C can make a big difference in power readings and it takes quite a while for something like a crankset to reach the ambient temperature of the air around it- so it's definitely worth letting it recalibrate a few times if you're going from a hot to cold environment.0
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Just as an example, I've attached my power trace from a ride which shows the first portion highlighted in red where you get a good indication of steady power, and relatively steady HR.
Just to the right of the first section, the power drops by about 20-25 watts, and you can see the HR increases by about 4-5 bpm. The odd thing here is that there wasn't any freewheeling as I've checked my cadence, and I didn't stop pedalling. Then in the yellow section there is a more subtle shift. As you can see I don't freewheel often - on this ride checking cadence, I only freewheel 5/6 times over 2 hrs.
I hadn't taken my bike outdoors before hand with this ride (indoor temp to 4/5 degrees outside), and forgot to do it again this morning - similar, but more subtle thing happened and I'd call it in tolerance (ok, just outside at say 3% ish).
As I can explain these oddities, I'm actually really happy with my P2M - It's so robust and it's been through everything this year so maybe it should have a service or something.
One question, can anyone confirm if the temp compensation also happens as you pedal, or on freewheel? Just want to check.0
