Matching CT Watts to Your PM--Resetting Procedure
This is the time of year when folks who own Computrainers begin to fret about the fact that CT and power meter watts don't match, and what guage to use indoors. Personally, I think you can work it out either way to your best advantage. However, Keith and I found the following on how to reset your CT to agree with your power meter. Disclaimer--we haven't yet tried it, but here it is FYI.
Permanent re-settimg
-if, once warmed up and calibrated, your computrainer doesnt agree with your powertap, you can adjust it 1x (ill call this re-setting) so that it permanently agrees (once daily calibrated) with your srm/powertap
Resetting procedure:
1) loosen the retaining allenkey on the flywheel, move the flywheel as far out on the axle as you can, tighten it back on (more room to work)
1b) look at the computrainer load unit- there is a sticker on the "wheel side" at about 9oclock- ie away from your front wheel, on the right side of hte computrainer faciing forward.
1c) remove this sticker
1d) under the sticker is a small hole
2) ride for 15 mins, recalibrate the tire pressure a bunch fo times. Make sure everything is warmed up, temp stable, etc
3) put computrainer in "erg mode" and put powertap in "lap mode" and have it display "avg lap power"
4) ride at steady RPM for about 5 mins, and watch how your avg lap power compares to your 'erg mode power"
5) stick a small screwdriver (i cant remember if phillips or flat) into the hole you found earlier
6) you will find a small screw deep in the hole with your screwdriver
7) turn the screw clockwise to increase powertap wattage, coutnerclockwise to decrease it. you should only turn the screw a tiny bit- like 1/8th of a full turn per adjustment
8) repeat steps 2-7 until your powertap and your computrainer agree on the same wattages
Comments
Nice work! Wiki post?
not sure where you found that nugget of knowledge, but any chance there is more there?? Looking for guidance on the calibration number on the CT. It comes preset at 2.0, but the manual is very clear it needs to be calibrated every ride. The manual is very vague as to what the number should be. I've heard anywhere from 2.0-2.5 and even 2.7. I've also read it doesn't matter that much as long as you are consistent from ride to ride. Is there some engineer that has figured this out, or is it really just that vague?
@Tom:
I've found that it's just that vague. The rolldown calibration number you get will simply depend on how tightly you've adjusted the roller to the wheel.
Back in the day I ran/managed a CT studio and called CT about this. I believe they said 2.0-2.2 was ideal. Maybe email them or search The Google to comfirm?
Rich, I think it used to be, my paper manual circa 2005 says 2.0 the newest stuff on the CT site (last I checked) said at least 2.5, when I spoke w/ them a few years ago they also recommend the conti indoor trainer tire.
Will wiki it!
Now we have to do some caliibration research and get that straight. I'm have a little confusion too. Have always calibrated to 2.2-2.5. But at the EN Team TT at the Tri Expo, the guys there have you calibrating the CT to 2.5-3.0, which I have never heard of. That still rings in my head making me wonder what's right? I've stuck with 2.2-2.5, but now I wonder.... Whoever ets to the bottom of it first, post back.
FOR PURPOSES OF CONSISTENCY, ALL COMPUTRAINER ROLLING RESISTANCE
CALIBRATIONS (RRC) SHOULD BE PERFORMED AT A LEVEL EQUAL TO OR HIGHER
THAN “2.7".
That was written in 2004. His thoughts - crush your tire. Sure it will wear out fast, but at least it's accurate. Even better, use an indoor tire.
I've rarely been able to register that number after a 10 minute warmup. Usually closer to 2.2 or 2.3.
You can get there if you calibrate within the first minute at are at ~3.2-ish.
Then after warm up, calibrate again, and it will likely come down to that level. Alternately, like you say, warm up, calibrate, then crush the tire until you get to that number. I have to say, trying out that higher calibration--I really like the way it feels when I ride. Nice and grippy. I've just been staying at the lower numbers b/c I thought it was "correct."
Last year I keep it 2 to 2.5. However, I'd get a ton of slippage when doing certain course, such wildflower. But, I was using normal tires too. I will start using 2.7. Thanks!
For the life of me, I cannot find the "small hole at 9 o'clock" that has the adjustment screw inside. Any hints??? Mine is late 2007 vintage. The serial number sticker is there, but no hole under it.
Thanks, Chris
Regarding CT calibration; In one of the manuals I received with the CT there is a table of caibration values referenced to both grade of a climb and watts. As watts increase the calibration value needs to increase to prevent the tire from slipping. I find that the 'warmed-up' value after 10 minutes of riding is generally around 0.5 less then when I first start up.
Now if I can just figure out how to determine FTP from my 42min test on the CT (don't have WKO+...yet). Got until tomorrow morning...starting NOV OS!!