RE: SRM vs Tacx Grand Excel - Wattage Readings http://64.125.140.196/lists/wattage/read/message.html?mid=903671826&sort=d&start=2138	Garth Rees
	Mar 04, 2002 09:43 PST

A couple of points first. There is hidden in the Wattage archives a reasonable "dead-man's weight" calibration test for the SRM, of which a number of list subscribers have used to check and correct their SRM's. Assuming the SRM is correct...... The error is linear (in terms of %age), so it may be the calibration factor in the Tacx. (only 1 of 100 are check-cal'd off the production line, I'm informed - which is usual for electronic batch production) Tacx calibration procedure..... Ensure the tyre pressure and the roller pressure are identical to when the original test was done (better to repeat the comparison, just before and after calibration, which only takes a few seconds). Power down the Tacx. Hold the "Set" button down and re-apply power - DO NOT RELEASE until you have heard the 2nd "beep". The display should show a flashing number in the lower right corner, the default is 100. The range of adjustment is 80-120, based on the info you gave, you should move it up to 101 or 102. Save the change ("Store" with the white button) Power the unit down, then re-start it. Whatever munber you set should appear in the lower right during the boot sequence. Check against the SRM, and re-adjust as required.   I have suspicioned that my Tacx Grand Excel wattage readings were suspect, so yeterday a fellow teammate and I set up his bike on my Tacx. His bike is equiped with a SRM system so we could get both sets of wattage data. The findings were significant. All of the readings were taken with wattage stabilized for at least 10 seconds as to hopefully avoid any lag or smoothing process by either system.           Tacx Excel     SRM     Difference     % Difference             80 w        100 w       20 w          20% lower            160 w        200 w       40 w          20% lower            250 w        300 w       50 w        16.67% lower    The question now is which one is correct. Our non-scientific conclusion is that the Tacx is giving the incorrect readings based off of a VO2 Max Test that I did based off of time at sustained wattage increments. The VO2 results on the Taxc were 50.4L/Kg, which seemed a little low (and somewhat deflating to the ol' ego...understatement). My Bio's are: Age: 46 Weight: 78.47 Kg Height: 1.88 m RHR: 39 BPM MHR: 180 BPM 40k TT: 0:59:02 So, based off of bio's and assessing a value from the SRM VO2 Max would come in at around the 60L/KG level, which I think (hope) is more accurate. All this said can anyone suggest what I can do to calibrate the Tacx to a correct wattage reading. Thank you, Jack Richards