PNorm drop 269W to 220W on same TT course - but I went faster?
6 weeks ago, two weeks after I got my P2 with PowerTap, with no idea what sort of power output to expect in race conditions, and still learning how to ride the bike, I raced my cycling club's 9.2 mile flat time trial on a warm windless evening: time 24:15, HR 167, VI 1.01, PNorm 269W.
Last night, same course in cold windy conditions: time 23:20, HR 169, VI 1.01, PNorm 220W. So I worked harder HR-wise, finished nearly a minute faster, but my norm power dropped by nearly 50W? I was probably racing at less than peak power last night, thrown off a bit by wind and cold, maybe a bit fatigued by the morning's 1-hour swim workout (though it was kickless) and the previous day's bike intervals. But I've never been able to come close to the 20-minute power output of that first time trial, either before or since. BTW, I've never done a formal 2x20 FTP test; I thought the time trials would be an adequate substitute, since the race would motivate me to push harder than I would indoors on a trainer. But now I don't know what to think.
Could my PowerTap have gotten that badly miscalibrated on that one race? If so, how often should I be calibrating it - before each ride? Any tips to ensure accurate calibration?
Comments
Tough to compare two different rides and tell you why you're faster with less power etc. Assuming all the equipment/clothing/position was the same - the conditions may have just produced a faster split. Were the overall speeds faster for the group or just you?
It wouldn't suprise if that you produced less power coming off bike intervels within 24 and a previous workout that morning. If you're going to rountinely do this event, set up a excel graph and plot your power and speed and fill in some notes about the day.
Oh, and do an FTP test
Was this an individual TT or in a group? Were you drafting? That could explain the lower watts but faster time.
Wind however has a way of really changing the course. I have a hard time hitting FTP watts when the wind is at my back- but I'll be screaming fast. You say it was windy, but what direction was the wind and how did the course relate to to the direction of that wind?
Also- what are you using as a computer for your PT?
I think the questions of wind direction and group riding need to be answered. I also agree with the OP question about calibration. I try to do mine weekly to be consistent. I also find that it is way off after I change any batteries and it does make a huge difference.
Dan
Individual time trial, no drafting. Same equipment and clothing, locked in aero position both times though maybe a bit more comfortable in it now. Of the three other riders that did both time trials, all of whom beat me the first time, one was 1:37 faster last night and the other two were slower by :27 and :43 (beat him!). A strong tailwind would certainly explain the results, but it felt more like a cross- or even a head-wind, and those two riders who slowed down don't seem to have benefited from it.
The PowerTap is brand-new. I'm using the yellow head unit that comes with the PT, and uploading the results from it to WKO+. My PT manual says "Frequently the torque must be zeroed to ensure the most accurate power information is displayed...while stopped, with no tension on the chain, no tension placed on the pedals". Just wondering if it could have gotten far enough out of whack to screw up the data from that first TT. Because I'm finding myself disbelieving that 270 PNorm.
Weather permitting, in two weeks we do the same route but as an out-and-back (18.4 miles). If I can ensure it's a fair test (well rested, warmed up, PT reading accurately, anything else?), can I take that as my FTP? Please don't make me go back inside.
Almost forgot to mention - I wiped down the frame with Lemon Pledge yesterday afternoon. Maybe that's the secret to the faster time?
I have an older PT, and we zero the torque before every single ride. Why not? One less variable to worry about. Sometimes we zero the torque mid-ride too. I know Rich used to do that with his Ergomo. I will say that sometimes my PT starts going fluky just before it needs new batteries. Nothing is blinking, it just gives an "off" reading, no matter how zeroed.
Regardless, nice work out there!
Mike
Then it sounds like the thing to do is to race the 18.4mile TT and then just keep going until I reach 40k or 1 hour, whichever comes first (probably the hour, hopefully not by much)? I'd get some funny looks from the rest of the club but WTH.
can I strongly talk you out of doing that? Absolutely no need to do a 40k TT to establish FTP. See Coach Rich's opinion on that in the wiki. You should already have plenty of data from a 40+ minute effort to get a good estimate of FTP.
Especially if this is a repeating TT series, just do what the prescribed distance is.
Mike
The out and back course in two weeks would be ideal for the test. The only catch I can see... Is this a TT race again. The 23' TT is the perfect distance for you to do a 2X20' with 2' rest. Now if this is a race then without the 2' rest you will have a overestimation of your FTP as you did not complete a 1 hour TT.
How you would adjust a 48-50' TT to estimate your FTP is a personal question.
As Mike said you don't have to do the 60' TT, but that's how its actually calcuated by Dr.Coggan.
The other down side is that you will have to go a little easier and may not beat those other in the TT. You will need something left in the tank to complete the 60' while the other can hammer harder.
I'll have to try the pledge to see if it get me a few extra seconds.
Gordon
Yes. that's close enough for your purposes.
Honestly, I don't really believe in using a PM to pace a Sprint. It's very close to an all-out effort. I'd say the only value in a PM for a Sprint is maybe the first 5min just to make sure you don't go too crazy.
Thanks, Chris