problems with PT

live2trainmore said:

thinking about getting an ibike to validate the numbers

That would be a first ????

live2trainmore said:

having problems with PT accuracy. watts seem to be low. sent it to saris and they rebuilt the entire unit...calibration was low. unreliable/low watts on the first ride upon it's return...sent back again to have the torque tube replaced. watts still seem to be suspect over the course of entire ride although they looked good for a 1 mile hard effort test...perceived exertion just doesn't equate with the numbers. it's been some time since i've done a 20:00 threshold test..mostly because i've been farting around with this...so it's possible TH could be off and skewing the numbers. that said, i live in a warm climate and ride all year long so level of fitness doesn't have significant peaks and valleys. it wouldn't be off by much. thinking about getting an ibike to validate the numbers and perhaps ditch the PT. PT is only 1 year old...i shouldn't have to do this, but going on 6 months now and i need to move on and get down to training. any reason why i can't mount both on my bike? will interference occur?

any sugestions greatly apreciated.

LK

On what basis were you measuring or estimating your power before the PT?

Alex Simmons said:

On what basis were you measuring or estimating your power before the PT?

the PT worked january through september..my basis for measuring power was the PT istself. the watt readings started appearing lower and didn't equate with HR readings and perceived exertion. it was also unlikely that my level of form would drop so suddenly without reason. i also looked at previous CP downloads for same courses in attempt to validate my suspicions. after that i put my bike on my computrainer and compared the 2 readings....the PT was generally 40 watts lower.

live2trainmore said:

having problems with PT accuracy. watts seem to be low. sent it to saris and they rebuilt the entire unit...calibration was low. unreliable/low watts on the first ride upon it's return...sent back again to have the torque tube replaced. watts still seem to be suspect over the course of entire ride although they looked good for a 1 mile hard effort test...perceived exertion just doesn't equate with the numbers. it's been some time since i've done a 20:00 threshold test..mostly because i've been farting around with this...so it's possible TH could be off and skewing the numbers. that said, i live in a warm climate and ride all year long so level of fitness doesn't have significant peaks and valleys. it wouldn't be off by much. thinking about getting an ibike to validate the numbers and perhaps ditch the PT. PT is only 1 year old...i shouldn't have to do this, but going on 6 months now and i need to move on and get down to training. any reason why i can't mount both on my bike? will interference occur?

any sugestions greatly apreciated.

LK

Why don't you test the accuracy of your powertap?
midweekclub.capowerFAQ.htmOpen ↗

Also search this forum for "calibration", or "stomp test".

More than likely, whatever you were using to measure power before the power tap was reading high. That's not uncommon. You're fortunate that, of the available powermeters, only the PT and the SRM can actually be checked against reality.

I can believe a PT reading low, as I've actually seen one. But I have a hard time believing it came back from a rebuild still reading low.

You've zeroed the torque as well, right?

jbvcoaching said:

Why don't you test the accuracy of your powertap?
midweekclub.capowerFAQ.htmOpen ↗

Also search this forum for "calibration", or "stomp test".

More than likely, whatever you were using to measure power before the power tap was reading high. That's not uncommon. You're fortunate that, of the available powermeters, only the PT and the SRM can actually be checked against reality.

I can believe a PT reading low, as I've actually seen one. But I have a hard time believing it came back from a rebuild still reading low.

You've zeroed the torque as well, right?

Before the PT I wasn't training with power...i was doing it the old fashion way so those readings weren't high...they weren't at all. The PT worked and then it didn't. My TH is 181 and I started to see numbers < 100...that is not likley. I was convinced that something was wrong when I got a speed reading of 95mph with a max wattage of > 1000....my training was coming along well, but not that well. After they completely rebuilt it and returned it to me my first ride showed a speed of 75mph and a max watt in the 700 range while drafting...also not likely. Yes, I zeroed the torque multiple times.

Also, my computer is set to display data every second. When is stop pedaling the display still reads a value. the value goes down and then appears with a zero. that process takes more than 1 second. i would think you would see zero whenever the crank arms aren't turning over??

Lynne

live2trainmore said:

Before the PT I wasn't training with power...i was doing it the old fashion way so those readings weren't high...they weren't at all. The PT worked and then it didn't. My TH is 181 and I started to see numbers < 100...that is not likley. I was convinced that something was wrong when I got a speed reading of 95mph with a max wattage of > 1000....my training was coming along well, but not that well. After they completely rebuilt it and returned it to me my first ride showed a speed of 75mph and a max watt in the 700 range while drafting...also not likely. Yes, I zeroed the torque multiple times.

Yes, that sounds wrong. Is this just the odd, instantaneous data point, or is it something that happens regularly? If it's the latter, you've got to call Saris & send it back again, insisting they fix it properly. They certainly are capable.

Quoted post said:

Also, my computer is set to display data every second. When is stop pedaling the display still reads a value. the value goes down and then appears with a zero. that process takes more than 1 second. i would think you would see zero whenever the crank arms aren't turning over??

Lynne

Yes and no, it can update the display every second, but it's typically also set to average the power display over 2-3 seconds (I can't remember the default, but it's one of those), so even updating it more often will not necessarily make it read zero faster.