PowerTap Watts Too Low

gimpy_calfee said:

I have 2 powertaps a standard and a pro cpu with wired harnesses, one is shark fin other is not. Anyway, yesterday on the bike without the sharkfin harness both cpus read really low watts (felt like 300, read 90). I zeroed 4 or five times without any change and then switched bikes in my trainer. Both cpus read normally, and I did my workout. Does anybody know what is up?
Scott

Sure sounds like a harness problem. You should do a static torque test (stomp test) on both bikes: http://www.midweekclub.ca/powerFAQ.htm#Q23 so you have good numbers to compare. If the torque tests reveal similar numbers then it has something to do with how one setup relays speed information but it sounds like you already have enough info to figure out one harness isn't giving you good results.

gimpy_calfee said:

I have 2 powertaps a standard and a pro cpu with wired harnesses, one is shark fin other is not. Anyway, yesterday on the bike without the sharkfin harness both cpus read really low watts (felt like 300, read 90). I zeroed 4 or five times without any change and then switched bikes in my trainer. Both cpus read normally, and I did my workout. Does anybody know what is up?
Scott

I'm confused, do you have 2 different wheels as well? Or, do you have one wheel which you swapped when you changed bikes?

If you have one wheel, sounds like a harness problem. If you have 2 wheels, you need to do a bit more troubleshooting to figure out if it's the one wheel or the one harness.

"Stomp" tests with all combos of harnesses, cpus, and wheels will reveal all 😉

Switch the wheels and re-test. The error will be either on the bike(harness or head) or the wheel.

Thanks all. Tom, I have 2 wheels and switched the cpus from bike to bike. It makes sense if I switch the bad bike wheel to the good bike and it works, its the harness and otherwise its the hub. Atleast I think it makes sense. Now I am confuse.....

I've never seen a receiver change the reported power. When they fail, they just fail. Sounds to me like one of the hubs, since the CPUs report consistently on each hub (i.e. - both low on one, both accurate on the other).

gimpy_calfee said:

I have 2 powertaps a standard and a pro cpu with wired harnesses, one is shark fin other is not. Anyway, yesterday on the bike without the sharkfin harness both cpus read really low watts (felt like 300, read 90). I zeroed 4 or five times without any change and then switched bikes in my trainer. Both cpus read normally, and I did my workout. Does anybody know what is up?
Scott

you could check the hub bias/offset thru Setup ... Debug or Test mode (check the manual!) . One of the screens there gives you the unloaded reported number from the hub. Should be around 512 but if it goes off significantly from there it can't correct. My m/b PT hub was down around 300-315 last fall and the power simply read around 200W low. Rather disturbing the 1st time it happened!

rmur,
How did you fix it? I didn't have time last night to work on it. Probably won't til Saturday. But, that sounds like the problem. Do I have to send the hub back in as was suggested above? (Noooooooooooooo..............)
Scott

rmur17 said:

you could check the hub bias/offset thru Setup ... Debug or Test mode (check the manual!) . One of the screens there gives you the unloaded reported number from the hub. Should be around 512 but if it goes off significantly from there it can't correct. My m/b PT hub was down around 300-315 last fall and the power simply read around 200W low. Rather disturbing the 1st time it happened!

gimpy_calfee said:

rmur,
How did you fix it? I didn't have time last night to work on it. Probably won't til Saturday. But, that sounds like the problem. Do I have to send the hub back in as was suggested above? (Noooooooooooooo..............)
Scott

aye had to send it back ...