I have asked this before but here we go… I am weak on the CT. according to my coach, I should easily av 200 watts for these workouts I do. well i did 5 x 5 min ALL out intervalles and got 193,189,176,175 and 162. All winter I beat myself up for being so weak. Yet i did race ok. well I had a friend over tonight with a SRM and he wrote my CT. Wattage was consistently off by 25-40 watts. I had called computrainer and they said that very rarely, something is wrong with the generator and the wattage is off. i could send it in if I want (don’t want to do that now). I want to know if anyone has experienced such a drastic wattage difference on CT versus their power tap or other device.
I know it’s all about how I improve from there but still, I would be happy if really, instead of putting out 175 watts, I really was putting out 205.
You should never trust the wattage on a Computrainer as being absolutely correct. Perhaps relatively correct to itself for determining changes in fitness. Many people have found they have to use either a known PowerTap or SRM to calibrate their Computrainer. If your coach is ignorant of this fact, consider getting a new coach.
Maybe your Computrainer is right and his SRM is not?
Also, there are differences between the power measuring devices, for example, a Powertap may read differently than SRM due to one reading power at the hub and one at the crank.
40w is pretty large however - I would send it back, but not until I get someone else with a powermeter to give a second opinion.
I have asked this before but here we go… I am weak on the CT. according to my coach, I should easily av 200 watts for these workouts I do. well i did 5 x 5 min ALL out intervalles and got 193,189,176,175 and 162. All winter I beat myself up for being so weak. Yet i did race ok. well I had a friend over tonight with a SRM and he wrote my CT. Wattage was consistently off by 25-40 watts. I had called computrainer and they said that very rarely, something is wrong with the generator and the wattage is off. i could send it in if I want (don’t want to do that now). I want to know if anyone has experienced such a drastic wattage difference on CT versus their power tap or other device.
I know it’s all about how I improve from there but still, I would be happy if really, instead of putting out 175 watts, I really was putting out 205.
Do you understand the correct method of calibrating your computrainer? Without calibration the numbers are worthless. With calibration they should be pretty good.
Since you are not big you do not need to produce as many watts to go fast. I remember last year during the Ironman that there was a webpage which showed several cannondale athletes wattage in real time. Hellriegal and Al Sultan were pushing 250-260 watts while Fernanda Keller was going like 160. I think of Fernanda as one of the most consistent Women pros ever at the Ironman distance.
Also there is a thread on the Gordo Forum where a 60 KG (132 lbs) guy averaged 180 watts and rode 4:51.
SRM measures power at the crank. A chain-and-sprocket drive train is approximately 96% efficient (at the maximum – that is cleaned, lubed, aligned right, etc.) Then you have the error for the SRM, which is between 2-5%, depending on which model he has (I’m gonna go ahead and say he doesn’t have the science one, which is 0.5% accurate). And that is when it is calibrated correctly. Then you have error in the computrainer calibration. Did you properly warm-up your tires and the unit before calibrating? Again, even assuming you did, the Computrainer is no more accurate than the SRM, so let’s assume it’s also 95% accurate.
Even if both the computrainer and the SRM were 100% accurate, you’d still see a difference of 8 watts between the crank and the wheel just to normal drivetrain losses at 200 watts.
Even with everything calibrated perfectly, you could still see as much as 20 watts variation. And that is assuming perfect calibration.
“Do you understand the correct method of calibrating your computrainer? Without calibration the numbers are worthless. With calibration they should be pretty good.”
Well I think i do… I ride for 10-20 minutes, something 45 and then calibrate the trainer, save it (F3) and try to keep the press on force somewhat similar, around 2.0
That is interesting data… that’s the kind of stuff I am looking for. all I can tell you guys is that we used to do these challenges every week, and I was almost always dead last. And with my performances, I was told that it was unlikely. therefore, I thought the CT was off… But I like that you came up with data for me about that 132 pound guy…
Which helmet
Which front wheel
Which rear wheel
Shoe covers?
Skinsuit?
I’m getting a pretty good handle on my watts now with my SRM, and I’d like to know what kind of speeds I should expect 1) to know how much I might improve my position, 2) how much I might further reduce my CdA through equipment choices
Thanks. You and I weigh about the same. I’m a hair lighter, but also probably taller (6’3", 73kg).
One really cannot depend upon the absolute value of wattage from one Computrainer to another Computrainer even when using the correct protocol to set it up. If one uses the same Computrainer all the time, one can track a relative change in performance as they are relatively stable that way. So one could chart an improvement if one starts consistently putting out higher numbers. But to depend upon absolute wattage numbers output on different Computrainers that have not been verified to be accurate is contrary to all evidence of people who have actually tried to verify the accuracy of their Computrainers or any uncalibrated power meter for that matter.
Which helmet - Bell Vortex (circa 90’s) very low profile for my head
Which front wheel - 999 tubular, conti 22mm comp
Which rear wheel - 999 tubular, conti 22mm comp
Shoe covers? - Carnac lycra
Skinsuit? - long sleeve Squadra/Castelli lycra
I am 6’0"
Got a Ritchey adjustable stem dropped all the way, HED bar no shims, 130mm drop from top of saddle to elbow cups
Have some testing to do before I commit to the new position, of course, but I like it so far
'05 Arcole, all DuraAce 10sp, SRM D/A cranks w/Rotor Q-Rings, Ouzo Aero Pro fork, 999’s, thomson 25.0 post and Alias Ti saddle
I dropped my bar so low that I had to ditch the Hooker front brake, centerpulls would not work
I know I need to get lower in the front… I’m running 120mm. My bike has a head tube extension on it (which I would have specifically asked not to have had I known they’d put it on). I need to get the builder to shave it down to give me another 20mm. After that, I think I’ll need to start trying a new stem. Right now I want to go lower. It feels like my shoulders are being pushed up from where they would naturally settle.
I’m getting a LG Rocket, and will be modding it myself (if neccessary a la Zabriskie’s/Basso’s Meteor’s) to sit flush with a bit of handy carbon fiber trickery.
I’m also saving for the 999’s. I run HED Stinger 5.0’s which I’m not happy with.
Also running the HED bars.
Also running D/A-10 with SRM. Ouzo Peleton Fork. Same Thomson seatpost. Fizik Aliante saddle.
What’s your opinion on the Ritchey adjustable stem? Good for trying out new positions? How much more drop could I gain from that? I’m running a 110mm/86deg stem going down right now. HTA is 73deg.
