Powertap Calibration Postride

sglasgow said:

Is there anyway to check after the ride that the power figures are accurate? I understand that you need to make sure that power indicates is at zero when coasting. I did not pay attention before doing a 10 mile TT to determine FP.

Thank you,

didn't you coast at all during the ride...either before or after? fwiw...my PT very rarely shows anything other than zero when checking the torque before a ride.

sglasgow said:

Is there anyway to check after the ride that the power figures are accurate? I understand that you need to make sure that power indicates is at zero when coasting. I did not pay attention before doing a 10 mile TT to determine FP.

Thank you,

Check the torque readings in the downloaded PT file for the ride plus any time either side of the TT where you may have done some coasting - during warm up/down perhaps. Looks for extended periods of zero cadence. If your torque readings are zero when coasting, then all is OK. If not, then you'll need to do an adjustment of the data. If you have no periods of coasting at all, then it will be pretty well impossible to tell. Here are the instructions posted by John Verheul several years back.

[font=Geneva]1) Open the PT file in Excel.
2) Sort it by torque (ascending) so you find the lowest torque value (or, as
chris says, just look for periods of coasting and observe the torque there).
3) Click Edit -> Undo to put the file back in it's original order (or
re-sort by time).
4) Create a column that is a formula, you want to subtract the lowest
observed torque value from the torque column. Column should be as long as
the file itself.
5) Calculate power using the new torque using the instructions Rick Sladkey
gives in the FAQ. That is, power = 1746*recalculated torque*(speed/2093).
Adjust the 2093 number (which is wheel circumference) if using other than a
700x23 wheel/tire.
6) Copy the new power cells and paste -> special (values) over the original
power column. Do the same with the new torque values.
7) Delete the now extraneous recalculated columns, save the file as a .csv
again, and now import into CPSoft.
8) Lobby Hunter & company to add the torque-zero-fix to CPSoft (along with
an SRM slope fix). :-)

John Verheul [/font]

Alex Simmons said:

If you have no periods of coasting at all, then it will be pretty well impossible to tell.

John Verheul [/font]

Well that's the case I wanted only the TT so I pulled the computer at the finish line. I looked today and the Torque reading was 1. I have now reset.

Sean

sglasgow said:

Well that's the case I wanted only the TT so I pulled the computer at the finish line. I looked today and the Torque reading was 1. I have now reset.

Sean

Just hit both buttons to place an interval mark in the data when you finish the TT. You can look at the interval then and can also keep all the other data.

Alex Simmons said:

Check the torque readings in the downloaded PT file for the ride plus any time either side of the TT where you may have done some coasting - during warm up/down perhaps. Looks for extended periods of zero cadence. If your torque readings are zero when coasting, then all is OK. If not, then you'll need to do an adjustment of the data. If you have no periods of coasting at all, then it will be pretty well impossible to tell. Here are the instructions posted by John Verheul several years back.

[font=Geneva]1) Open the PT file in Excel.
2) Sort it by torque (ascending) so you find the lowest torque value (or, as
chris says, just look for periods of coasting and observe the torque there).
3) Click Edit -> Undo to put the file back in it's original order (or
re-sort by time).
4) Create a column that is a formula, you want to subtract the lowest
observed torque value from the torque column. Column should be as long as
the file itself.
5) Calculate power using the new torque using the instructions Rick Sladkey
gives in the FAQ. That is, power = 1746*recalculated torque*(speed/2093).
Adjust the 2093 number (which is wheel circumference) if using other than a
700x23 wheel/tire.
6) Copy the new power cells and paste -> special (values) over the original
power column. Do the same with the new torque values.
7) Delete the now extraneous recalculated columns, save the file as a .csv
again, and now import into CPSoft.
8) Lobby Hunter & company to add the torque-zero-fix to CPSoft (along with
an SRM slope fix). :-)

John Verheul [/font]

Sorry to hijack this thread...but would you know how to do this if the file was only downloaded in to CP?? When I try to open the file all I get is a jumbled mess....thanks!

RipVanCommittee said:

Sorry to hijack this thread...but would you know how to do this if the file was only downloaded in to CP?? When I try to open the file all I get is a jumbled mess....thanks!

Save/export the file in CP as a .csv file format and you will then be able to open it in Excel. When done, you can import the new .csv file back into CP.