Posted by Herb (207.200.150.64) on November 07, 2003 at 16:13:40:
In Reply to: Re: Tacx Calibration Follow Up posted by Joe Scho on November 07, 2003 at 12:25:02:
: For calibration purposes using only the speed reading, obviously speed is very important: You are using this in the calibration procedure whether you use 30 Km/h or 40 Km/h as your starting point in a roll-down test. From what I understand, at the zero resistance setting the speed calculation does not incorporate body mass or height or any other parameters. It makes sense to me to use the pressure on the tire as a way to calibrate the system and not play around with the "scale factor". I simply wanted to know if the procedure outlined here was consistent with that outlined on the wattage list. How long does a roll-down take starting from 40 Km/h if it takes 6.08 sec from 30 Km/h?
The scale factor is there precisely for the purpose of calibrating the Tacx to an outside source to make its readings accurate. I don't know what was done on the Wattage list. I haven't done a roll down from 40kph so don't know. I used 30kph since this is the speed used for the built in calibration method for the new Tacx Flow. I don't understand how you can use speed to calibrate the resistance of the Tacx to give an accurate wattage reading. Why is speed important? No one trains with speed, too many variables - hills, wind, etc. Wattage and Heart Rate are the important factors for training.
: In principle, I agree that the power measurement is all that really matters unless you are competing with someone else via a performance file or over the net.
I would think that here it is very important that all the trainers give the correct wattage readings. How can you compare if your trainer's resistance is 220watts but is shows 200 watts and someone else's shows 200 watts but is actually only producing 190 watts?
: Furthermore, I think that if you have a powertap or some other reliable power meter I wouldn't bother too much with the tacx.
The Tacx is great for training and testing because of its programmability. why wouldn't I bother with it? Why wouldn't I want to set the scale factor so the Tacx gives accurate readings? Further the 6.08 second roll down time at 30kph at 200 watts now allows me to make adjustments for consistency when other bikes (without PT) are used on my Tacx.