CT, PT, Polar comparisons/discrepancies

kjanracing

I did the FTP test this evening on a CT using a PT rear wheel rom my wife's bike, and a Polar CS600 with power-the power meter I"ve used on my bike for a few years now.  When I've ridden the CT, the CT numbers and Polar numbers have been pretty close.  Yesterday I did a ride outside with the PT rear wheel and compared the readings with the Polar.  Again pretty close.

Hr ave= 128 bpm.    PT  W ave=128  PT normalized power= 154W.   Polar W ave=155.   note: maybe Polar is calculating more of a normalized power? 

On to the FTP test and comparison.     CT W ave=204.   Polar W ave=217   PT W ave=143  normalized power=159W   Hr ave=160bpm.  Notice the over 50W difference on average power between the PT and the other two and about 50W diff. on normalized power.

So, I do a ride yesterday, low heart rate,normalized power of 154W and this evening I bust my ass for 40 minutes and have,according to the PT, a normalized power of 159W, 5 watts higher than just going out and riding.  Something wonky here. 

When my wife got the Powertap and rode on the Computrainer, she noticed the same thing, the PT numbers being a lot lower.  In fact she averaged something like 80W on a 20 minute test!   And YES the CT was warmed up, spun up and calibrated and all that. This is also an older Computrainer, so I can't upload data.  Yes, the PT torque was zeroed, etc.  

Any ideas on all this?

My plan is to use the Polar for power, using the 217W as my FTP.   I did buy WKO+ thinking it could analyze the Polar power files, but it doesn't look like it will.  It will take the .hrm files though, so can I get useful info from the run files or even the bike files minus power?

opinions please...

time for bed and recovery sleep! Thanks!

Tom Glynn

Kurt,

You'll never have exactly the same power levels from multiple devices as they all calculate power using different equipment and use different math to analyze and aggregate the data.

Having said that, they are usually pretty close. Calibration issues can be huge problems. Sounds like you calibrated the CT. Did you let it warm up for 10+ minutes before calibrating?

How old is your PT? The newer models self calibrate. The older ones require you to calibrate when coasting watts do not equal zero. When coasting downhill, your watts should read zero, if not there is s step in the manual that explains how to calibrate. (It's pretty easy, but don't recall exactly how to do it.)

If both are OK, I would start by replacing the hub batteries in the PT to see if it makes a difference.

Can you borrow a friends wheel to test PT data?

WKO will take Polar hrm data and Garmin data. You should be able to get your CT data into WKO. The Coaching Software program allows you to export CT bike data to a text file, which can then be imported into WKO.

If you can't get any better PT data, I'd call the Saris customer service, they are excellent.

dan_forbes

 I can only give you my experience with polar.... I had a power unit from them a couple of years ago and it was the worst investment I ever made for my bike.  None of the power numbers were ever consistent from ride to ride and I really spent a whole day in total tweaking the unit to make it consistent.  Now, that being said, if your unit seems to be consistent, then it really doesn't matter what the readout is.  As far as wko, I thought it supported polar power files?  If wko doesn't support power files, I wouldn't buy it just for hr, your polar software is actually pretty good and you can use that instead.  Most typically use wko for power files and garmin files for running pace.  I actually think polars software is quite good if you work with it for a while.  good luck!

kjanracing

If I were to buy a power meter again, I'd prolly go PT or Quarq. I bought the Polar at Interbike a few years ago for a great show price and wanted to run my choice of wheels, anong other things. Joe Friel did seminars at the Polar booth and there was a max watts contest through out the day,and you could demo the Polar products and the unit seemed to work pretty well. I'ts been fairly consistant for me. When I did a road ride with the Polar and PT, the readings were really pretty close. I think there must be something in the p.a.u. in the Computrainer that messes with the PT hub's transmission. My wife will ride in the 130W range on the road and get on the CT and the PT will show ~80W...so still about a 50W difference. Whatever... On to the OS training! thanks for the inputs

Coach Rich

The Polar has been on the market for a while but has never attracted a firm following among serious power users (congrats, you're one, as a member of EN) due to the issues you describe.

Best to:

1. Sort out the PT, as Tom described.
2. Considering selling the Polar and use that for something else.
3. Sounds like you and your wife share the PT? Armwrestle for dibs?

kjanracing

Actually the PT is her's. I may have to body slam her for it! anyhow... I'll use the PT/Polar for the road rides and make a decision after a while. I'll have to accept that it's ok to train on a carbon race wheel, but she did all last year. We'll see...

Bob Irwin

Kurt - hope you'll post back when you get a resolution the PT issue.  I'm new to power, have a PT, and have always wondered how to tell if it was correct. 

kjanracing

Bob, the only time I have a problem with the PT is on the Computrainer. This morning it read really low again, too low to think there isn't a problem. Example, the CT and Polar are reading ~120W and the PT will be showing 30W. On the road, the power makes sense and agrees closely with the Polar. I think there is just a lot of interference from the CT power absorbtion unit, maybe the lights, maybe the intense radiation coming from the CRT of the 32"TV and maybe the sqiggley CFL bulbs that Algore loves that are in the overhead light just mess with the signal from the PT too much. I referenced heart rate along with CT power and felt like I achieved the intent of the workout. I'm going to use both the PT and Polar on my road rides and decide if I'll stay with the Polar or get a PT/wheel or Quarq. I think you did great getting a PT. It is one of the major players in power meters, you can't go wrong with it.

Michael Johnson

Wonder if the magnet in the CT wheel being relatively close to the PT hub could be affecting the reading. My PT FTP outside is 30-40w higher than the same test on the CT inside.

Michael Johnson

Im going to post this question on Slowtwitch tonight and see what they say also (hopefully the typical smartass comments will be avoided)

kjanracing

Please keep me posted. I may go over and try to find your post.