new ftp test

kjanracing

I got my SRM set up last week and did the OCT OS bike workout last weekend which started with 2x20min @ FTP.  I rode it more like a test, not trying to hold it to a number.  I had been using a Polar PM and the readings  are different between the Polar and SRM.  I think I'll put more faith in the SRM, ya think!!??  Would it be reasonable to get my FTP from that ride and new SRM numbers or should I do a test on the CT like I did for my first one?  Or did I really need to ask this question???

muchas

Coach Rich

Kurt,

Use the numbers for the SRM during that test as your FT. Completely ignore/forget any past numbers for the Polar and your CT is now just a fancy trainer. Don't look at it as a powermeter or compare CT to SRM watts. You'll go nuts.

stevekw

@Kurt, if it helps, Allen and Coggan in Training and Racing with a Power Meter do note that the PowerTap registers 5-10 watts lower than the SRM, since it measures power at the wheel hub (some power loss in the drivetrain)...and therefore measures the power getting to the road...instead of at the crank like the SRM

kjanracing

Rich, yeah it drives me nuts. Might use the eMotion rollers again and only look at the SRM. I could mount up my wife's PT and compare, but I ain't gonna do that neither. SRM from now on.

rkling

Kurt:

I agree with what Rich said; since you are going to be using the SRM outdoors as well as indoors, makes the best sense to use that to measure (and use the values to get your work efforts).  I've got a CT as well, and the CT and SRM tracked pretty closely together until this fall.  Then, my SRM numbers started reading much lower, which I couldn't explain.  Long story short, after adjusting the power sensor on my bike and recalibrating the slope on my SRM, it is now back to being very close to the CT numbers.  So, in that sense, having both helped me to get my SRM more accurate (at least to numbers that I trust better than before).

kjanracing

Thanks, Richard. I just got this unit back from being serviced so the batteries are new and it was just calibrated-hopefully the slope is correct. In a while I may try to check the slope and cal again. Do you check the slope on your's often? I've read the procedure of hanging a weight off the crank and goind through the calculations to get the actual slope. Has it changed much?

rkling

This was actually the first time I checked the slope myself. I didn't even know that this was something I "should" do until this year. It took some thinking to figure out how to do this logistically, but was pretty easy once I got everything figured out. I'll probably check it regularly now (at least every couple of months). My slope from SRM was 29.9. When I checked it, it was 29.2, enough of a change that the wattages went up enough significantly.

kjanracing

So that is about a 1% diff. Doesn't seem like a lot anyway...enough to really affect the reading? Oh but maybe the range between min. and max slope isn't between 0 and 100. That would make a lot if difference.