Power Values (Polar) - Realistic?

It would really help to know what you weigh, but nothing looks inconsistent with the info provided.

mises said:

It would really help to know what you weigh, but nothing looks inconsistent with the info provided.

180lbs (82 kg)

PolishPostal said:

Are these values realistic? I don't' have anything to base it on so I have no clue if these are accurate or not.

I was in the same situation as I have only just added a Polar system to my bike, but thanks to the great advice on this forum, and a bit of self testing I am confident that the Polar system, whilst not as good as PowerTap or SRM, is at least repeatable for your situation (ie you can gauge/see improvements).

The best bit of advice that I've been given, again here on this forum, was to plot my test values (http://velo-fit.com/articles/critical-power.pdf) on the Monod CP model. Suddenly, all the values I was seeing on the Polar started to make a LOT more sense and has made my training a lot more directed.

To my 'untrained' eye, those values look OK to me 😉

i had a polar on my machine last season, but without CP software. this season i got a PT Pro and CP2.0. i downloaded all of last season's rides into CP2.0 and to my surprise, found that my FP had not improved hardly at all after about 50 hours in the gym (in the late fall/winter), 150 L2 hours, and another 70 hours of L3/L4 mile (up to today).
Last season, according to Polar, my FP (from two averaged 40K TTs) was 225W at 76.4kilos. However, i discovered something curious: i ran a plot on the Mean Maximal Graph comparing last season's data with this season's data. i found that this season's Mean Max Power (which is composed of about 70% L2/L3 hours, and the rest L4) was significantly higher from about 1min and beyond compared to last years data. so if i was cranking out 225W according to polar and i am still cranking out 225-230W using PT Pro and yet i have made good gains from 1min out (i havnt really started on the L5+ yet, so no issues there), that indicates to me that Polar tended to over estimate. so in reality my FP last year may have been closer to 215W.

PolishPostal said:

Are these values realistic? I dont' have anything to base it on so I have no clue if these are accurate or not.

Based on your weight they look fine... and unless you are racing power #'s, it doesn't matter if they are off 10% as long as they stay consistent for you for training purposes. But they are definitely in the ballpark.

Here's what you need to do to ensure "accuracy":

1. Take an actual weight of your chain. Sometimes the manufacturers change the chain "mid-life" and the weight can be different than what's reported in the "table" values...ask me how I found this out 🙄 Also, make sure you enter the correct number of chain links. These 2 values are used to calculate the chain "density" and directly affect the power value reading.

2. Accurately measure and enter your chainstay length (center of the BB to center of the rear axle)

That's it. To paraphrase one of the developers of the system, if those values are correct, "...it either works or it doesn't". In other words, everthing else is just things you do to make sure it's going to read reliably...i.e. setup details.

Of course, one of those important setup details is to make sure the chain is never further than 25-30mm from the sensor top in your commonly used gears.

To tell the truth, I'm pretty impressed by your short term power numbers. The Polar tends to underreport those values due to it's averaging algorithm. That means you 5 sec (and perhaps 10 sec) numbers are actually a bit higher than what you show.

Let me guess...you're a pretty good sprinter, right? 😉

PolishPostal said:

Ok..... I just added the polar power sensor to my polar setup (got it on ebay for < $200). I did a fast group ride yesterday of 52 miles (20.6 avg) with 3000 ft of climb (5 climbs). I am now wondering if the power valued that I downloaded are realistic.

I'm a CAT 5 riding with a bunch of CAT 3's (and struggling to hang on). I would consider myself a strong CAT 5.

NP 280w
AP 201w
5s 1104w
10s 1016w
20s 1006w
30s 965w
1min 775 w
2min 569w
5min 379w
10min 286w
20min 271w
30min 252w
60min 234w

Are these values realistic? I dont' have anything to base it on so I have no clue if these are accurate or not.

Thanks.

To be honest I'm not really sure how good of a sprinter I am. I've never really heads-up sprinted against anyone of any caliber.

I'll double check my chain weight, length and chain stay length.

I typically never cross chain. I avoid the Big Ring to Big Cog and Small Ring to the 2 Smallest Cog combos. But in the big ring 2nd largest cog (in my case 23) I get what seem like very high values for my effort. It may have to do with the "not to exceed" value that you mentioned. I'll check it also.

Thanks for the reply!

I assume that you also have Polar Power? Do you utilize the Pedalling Index? I can't seem to get it much out of the 30's. My averages have been 17-20.

Tom Anhalt said:

Here's what you need to do to ensure "accuracy":

1. Take an actual weight of your chain. Sometimes the manufacturers change the chain "mid-life" and the weight can be different than what's reported in the "table" values...ask me how I found this out 🙄 Also, make sure you enter the correct number of chain links. These 2 values are used to calculate the chain "density" and directly affect the power value reading.

2. Accurately measure and enter your chainstay length (center of the BB to center of the rear axle)

That's it. To paraphrase one of the developers of the system, if those values are correct, "...it either works or it doesn't". In other words, everthing else is just things you do to make sure it's going to read reliably...i.e. setup details.

Of course, one of those important setup details is to make sure the chain is never further than 25-30mm from the sensor top in your commonly used gears.

To tell the truth, I'm pretty impressed by your short term power numbers. The Polar tends to underreport those values due to it's averaging algorithm. That means you 5 sec (and perhaps 10 sec) numbers are actually a bit higher than what you show.

Let me guess...you're a pretty good sprinter, right? 😉

PolishPostal said:

To be honest I'm not really sure how good of a sprinter I am. I've never really heads-up sprinted against anyone of any caliber.

I'll double check my chain weight, length and chain stay length.

I typically never cross chain. I avoid the Big Ring to Big Cog and Small Ring to the 2 Smallest Cog combos. But in the big ring 2nd largest cog (in my case 23) I get what seem like very high values for my effort. It may have to do with the "not to exceed" value that you mentioned. I'll check it also..

That's a classic symptom of the chain distance being too far in that gear combo. What happens in that case is that the vibration signal from the chain starts getting weak and it makes it more likely that the signal processing "locks on" to the signal generated by the chain pins passing the sensor. Depending on the cadence, this can cause a the high values.

Reset that chain distance and this problem should go away. Personally, I try to keep my max distance at ~25mm, even if it means rubbing in some of the small-small combos.

The sensor in the module is an ~1" square that's centered on the "middle" mark of the case. Make sure the chain ALWAYS passes over this 1"square zone. That will also make the readings more reliable.

PolishPostal said:

Thanks for the reply!

I assume that you also have Polar Power? Do you utilize the Pedalling Index? I can't seem to get it much out of the 30's. My averages have been 17-20.

Hmm...how could you guess? 😉

I don't ever look at the PI. To me, it's usefulness (or, lack thereof) is on par with spinscan numbers from a computrainer. Basically, without seperate force readings from the pedals, these numbers don't mean much since it's possible to get "good" numbers in ways that don't make you faster.

For similar reasons, I don't ever look at the left-right balance numbers either.

Personally, I wish the recording of these 2 values could be turned off and the extra memory used to either extend the power recording time or reduce the recording interval time. Are you listening Polar? 🙄

I made some adjustments to the sensor. I added some spacers. The gap is now down to 1 3/8" (Big Ring - 2nd to largest cog combo). I'm not sure that I can get it any closer. The front of the sensor is very close to the Front Derailer. It seems to be a bit more realistic numbers in that combo.

Todays Ride. (1hr 47mi, 33.9mi, 2105 ft climb, 19mph avg, 277w NP)

5s - 889w
10s - 863w
20s - 811w
30s - 757w
1min - 565w
2min - 413w
5min - 345w
10min - 303w
20min - 258w
30min - 254w
60min - 241w

Thanks for the tips Tom.

This accuracy issue is going to be impossible to state one way or another without another powermeter that can be checked for calibration or doing the long climb tests - the exact same issue with the Ergomo. A strong cat 5 could be anything - from someone who will upgrade to cat 1 in one season to someone who will struggle to stay with the cat 4's.

My numbers can be almost exactly the same as yours and I weigh 67 kg, and am a mediocre cat 4.

PolishPostal said:

I made some adjustments to the sensor. I added some spacers. The gap is now down to 1 3/8" (Big Ring - 2nd to largest cog combo). I'm not sure that I can get it any closer. The front of the sensor is very close to the Front Derailer. It seems to be a bit more realistic numbers in that combo.

Todays Ride. (1hr 47mi, 33.9mi, 2105 ft climb, 19mph avg, 277w NP)

5s - 889w
10s - 863w
20s - 811w
30s - 757w
1min - 565w
2min - 413w
5min - 345w
10min - 303w
20min - 258w
30min - 254w
60min - 241w

Thanks for the tips Tom.

I HIGHLY recommend you get it below 30mm...right now you're sitting at 35mm. IME that's too much.

If the front derailluer is in the way, slide the sensor module back a bit on the chainstay. Despite what the Polar installation instructions say, you don't HAVE to put the "middle" mark of the sensor on the middle of the chainstay. The main issue is being able to trigger the cadence sensor with the crank magnet. If the Polar supplied magnet prevents you from moving the power module back, it's a good idea to get a stronger rare-earth type magnet and either contact cement it to the backside of the pedal spindle (with steel spindles it may just hold itself there just fine) or to the side of the crankarm. The optimum approach with an "aftermarket" magnet is to line up the N-S axis of the magnet with the centerline of the bike. Don't point the N-S axis AT the cadence mark. I've found that the sensor is MUCH more sensitive to the magnet presence if you're triggering it with a magnet aligned the other way. Look at the Polar supplied magnet and you'll see that it's that way as well.

There's no reason you shouldn't be able to get the spacing down to under 30mm max....unless you have some sort of highly unusual setup. Heck, I was able to get one of my Polar PMs to work mounted to the UNDERSIDE of an elevated chainstay MTB. The sensor works just as well sensing the chain from below the case as it does from above!

Keep workin' at it...you've almost got it dialed.

Woofer said:

This accuracy issue is going to be impossible to state one way or another without another powermeter that can be checked for calibration or doing the long climb tests - the exact same issue with the Ergomo. A strong cat 5 could be anything - from someone who will upgrade to cat 1 in one season to someone who will struggle to stay with the cat 4's.

My numbers can be almost exactly the same as yours and I weigh 67 kg, and am a mediocre cat 4.

IME, once the setup is done correctly, there isn't anything to "calibrate" with a Polar and the numbers are dead on. Unlike the strain based PMs (Err-gomo, PT, and SRM) there's no flexible member which needs calibration and there isn't anything like strain gauge adhesive aging to change the values over time.

As long as the inductive sensor can get a strong signal from the chain vibration and read the frequency, if the chain weight and span length are correct, it's very simple math to convert that to chain tension. Combine that with the simple chain speed measurement and VOILA!...power is known. There's not a lot that can go wrong in there....

If it would make you feel better, a simple climbing test compared to an analyticcycling.com prediction is an easy check...but, IME, there really isn't any need.

dude,
i looked at your #s. I am a Cat 3 here in NC doing some hills. Looks like you got a strong 1 minute spike but otherwise, the #s look pretty believable based on my Polar. I've run a Polar and a Powertap now (after listening to a lot of people). I find the numbers comperable but the Polar does not hold anything well under 5 seconds which makes the high 700s suspect to me on your output but other then that pretty decent. What is your TT wattage?

Tom Anhalt said:

IME, once the setup is done correctly, there isn't anything to "calibrate" with a Polar and the numbers are dead on. Unlike the strain based PMs (Err-gomo, PT, and SRM) there's no flexible member which needs calibration and there isn't anything like strain gauge adhesive aging to change the values over time.

As long as the inductive sensor can get a strong signal from the chain vibration and read the frequency, if the chain weight and span length are correct, it's very simple math to convert that to chain tension. Combine that with the simple chain speed measurement and VOILA!...power is known. There's not a lot that can go wrong in there....

If it would make you feel better, a simple climbing test compared to an analyticcycling.com prediction is an easy check...but, IME, there really isn't any need.