when you zero the powerTap what is actually being sent to the CPU? hub offset + some sort of temp offset?
lately i've noticed that zeroing at different times during my ride (indoors on rollers) seems like the powerTap zeroing is always 'sliping'. every time i check it's never zeroed. start and it's +7 from the day before, zero it and do some of my warmup and it's +3, zero and just before i start my 1st interval and it's -VE.. zero again and after interval and sometimes it still zero or maybe +3... every time i check it's never zeroed.
when you zero the powerTap what is actually being sent to the CPU? hub offset + some sort of temp offset?
lately i've noticed that zeroing at different times during my ride (indoors on rollers) seems like the powerTap zeroing is always 'sliping'. every time i check it's never zeroed. start and it's +7 from the day before, zero it and do some of my warmup and it's +3, zero and just before i start my 1st interval and it's -VE.. zero again and after interval and sometimes it still zero or maybe +3... every time i check it's never zeroed.
any ideas what is going on?
1. batteries 2. auto zero turned off 3. rapid temp changes 4. cactus torque tube
1. batteries 2. auto zero turned off 3. rapid temp changes 4. cactus torque tube
1. brand new batteries 2. auto zero turned on... does this mean that zeroing is just not necessary.. can zeroing when auto zeroing is turned on cause a problem like this? 3. temp is basically same for whole ride 4. have no idea what a cactus torque tube is? corrosion? it's an SL they seem to be pretty much sealed...?
[Edit] calibrated using a weight... measured Torque = 44, calculated 46
1. brand new batteries 2. auto zero turned on... does this mean that zeroing is just not necessary.. can zeroing when auto zeroing is turned on cause a problem like this? 3. temp is basically same for whole ride 4. have no idea what a cactus torque tube is? corrosion? it's an SL they seem to be pretty much sealed...?
[Edit] calibrated using a weight... measured Torque = 44, calculated 46
Auto zero being OFF can see a drift happen occasionally. With it ON then a bit of coasting every now and then should always see it auro zero.
If the drift is not a lot and the power readings seem OK, then probably no big deal. Only other thing I can think of is to check cones/bearing etc (whatever the arrangement is on the hub) - it shouldn't matter but funnier things have happened.
Perhaps a call to Saris to get their opinion.
Cactus - slang for it's rooted, screwed, stuffed, not working properly. Back to base for service/replacement.
Auto zero being OFF can see a drift happen occasionally. With it ON then a bit of coasting every now and then should always see it auro zero.
If the drift is not a lot and the power readings seem OK, then probably no big deal. Only other thing I can think of is to check cones/bearing etc (whatever the arrangement is on the hub) - it shouldn't matter but funnier things have happened.
Perhaps a call to Saris to get their opinion.
Cactus - slang for it's rooted, screwed, stuffed, not working properly. Back to base for service/replacement.
thanks for the advice,
maybe i'll get in touch with Saris.. it's a problem because i'm doing the same speed/cadence and depending on when i last zeroed there can be a ~10-20W difference... really annoying.
I went through 6 powertap hubs on my PT300 indoor cycle because of this issue, have finally given up and just use heart rate. Cycleops said I was the only person they have seen this issue with. 🙄
I went through 6 powertap hubs on my PT300 indoor cycle because of this issue, have finally given up and just use heart rate. Cycleops said I was the only person they have seen this issue with. 🙄
Add me to that list. At first I thought it was the trainer that was the issue - not my 2.4 SL hub. However, a few sessions on the trainer later, I noticed that despite staying in the same gear and the same speed/cadence the power would drop anywhere between 10 to 30watts and then between 7 to 10 minutes later it would return. The transistion between the high/low and back to high was pretty quick - about 30 seconds, when it decided on what it wanted to do. There was also a reduction in torque.
Saris, basically said that they'd never heard of anything like this and from the graph I sent, they said that nothing was wrong.
What puzzles me a little is if the hub is also "calculating" cadence and speed as well as measuring torque and then calculating power - how do I know which unit of measurement or calculation is correct. Something tells me that there could a cadence sensor in my future.
What puzzles me a little is if the hub is also "calculating" cadence and speed as well as measuring torque and then calculating power - how do I know which unit of measurement or calculation is correct. Something tells me that there could a cadence sensor in my future.
The calculated/virtual cadence is independent of the power measurement which is based on hub torque and hub rotational velocity.
Not sure what's causing your other problem though.
lately i've noticed that zeroing at different times during my ride (indoors on rollers) seems like the powerTap zeroing is always 'sliping'. every time i check it's never zeroed. start and it's +7 from the day before, zero it and do some of my warmup and it's +3, zero and just before i start my 1st interval and it's -VE.. zero again and after interval and sometimes it still zero or maybe +3... every time i check it's never zeroed.
I'm glad I'm not the only one seeing this happening. I bit the bullet and from the recommendations of a good friend he said to get a used SL wired unit. As i started to do my typical 2X20 min intervals I could see that the second set was always lower in power than my first even though the speed and cadence was the same. I use the separate wired cadence sensor and use that as my guide instead of the power readings. I have been only using the PT indoors on my KK trainer.
I am going to try turning off auto zero and just use manual and see if that works for me too.
For the third time now I've sent my 2.4L in for recalibration in the last year. Saris says, " in the test mode, if the offset numbers arent between 506 and 520 that the torque is out off range and needs to be recalibrated".. They do not recognize the stomp or weighted torque testing.. (SRM testing).. From what I understand as the strain gauges get worn, it goes out of calibration easyer and faster??? This is per Saris??? No electrical device last forever, so don't rely on them...
when you zero the powerTap what is actually being sent to the CPU? hub offset + some sort of temp offset?
lately i've noticed that zeroing at different times during my ride (indoors on rollers) seems like the powerTap zeroing is always 'sliping'. every time i check it's never zeroed. start and it's +7 from the day before, zero it and do some of my warmup and it's +3, zero and just before i start my 1st interval and it's -VE.. zero again and after interval and sometimes it still zero or maybe +3... every time i check it's never zeroed.
any ideas what is going on?
Another idea is to auto zero with the bike out of the trainer. When out of the trainer also lift the wheel off the ground. Both of these relieve the pressure on the hub. Absolutely not pressure on the tire for best accuracy.
when zeroing the powerTap does the rear wheel need to be spinning?
yesterday i got ready to go outside for a ride and zeroed the PM before setting out (manual zeroing). then i noticed that the power was not zero as i coasted down a hill... +11 or something like that.
i'm thinking that you really can't test if the PM is really, really zeroed unless the rear wheel is spinning since no matter how it is offset, if angular velocity is zero (rear wheel not spining) power is always going to read zero no matter what. the only real way to test is to spin the rear wheel with no torque on the pedals to zero to see if it's zeroed properly.
but i guess the question i'm asking is, does the PM know somehow if it's really zeroed somehow if the rear wheel is not spinning?
Zeroing the torque on PT should always be done while coasting.
i just had a look at this... couldn't find my manual... Saris seems to be saying that it's ok to do stationary too...
http://www.saris.com/pdfManuals/308.pdf said:
IMPORTANT How To Zero Torque Occasionally, the torque must be zeroed to ensure that the PowerTap displays the most accurate power information. If the instantaneous power is positive or negative while coasting, the torque needs to be zeroed. This operation must be done while coasting with no tension in the chain or while stationary with no force being placed on the pedals. Also, the transmission icon must be illuminated. To zero torque, hold down the select (right) button for two seconds to enter torque mode. Then hold down select again until “0” is shown. Push select once to return to watts. The torque value will now read zero.
The way you zero depends on the firmware you are using. If it is a prior years PT and not upgraded to the Ant+ then the rear wheel must be spinning. If it is the new Ant+ then the rear wheel is stationary
doctorSpoc said:
when zeroing the powerTap does the rear wheel need to be spinning?
yesterday i got ready to go outside for a ride and zeroed the PM before setting out (manual zeroing). then i noticed that the power was not zero as i coasted down a hill... +11 or something like that.
i'm thinking that you really can't test if the PM is really, really zeroed unless the rear wheel is spinning since no matter how it is offset, if angular velocity is zero (rear wheel not spining) power is always going to read zero no matter what. the only real way to test is to spin the rear wheel with no torque on the pedals to zero to see if it's zeroed properly.
but i guess the question i'm asking is, does the PM know somehow if it's really zeroed somehow if the rear wheel is not spinning?
The way you zero depends on the firmware you are using. If it is a prior years PT and not upgraded to the Ant+ then the rear wheel must be spinning. If it is the new Ant+ then the rear wheel is stationary
just from my experience it seems like what you are saying is correct, but the above is from the instruction manual for my unit... i.e. PT SL wired.
just from my experience it seems like what you are saying is correct, but the above is from the instruction manual for my unit... i.e. PT SL wired.
Their "current" documentation available on the website isn't the best. I bought my 2.4 SL last year and the info in the "hardcopy" of the manual that I got in the box shows some different info than the copy that was available online just over a month ago.
Their "current" documentation available on the website isn't the best. I bought my 2.4 SL last year and the info in the "hardcopy" of the manual that I got in the box shows some different info than the copy that was available online just over a month ago.
What I meant to put was that the info in the manual I downloaded, for the 2.4 SL, had info in there that was relevant for the that specific model - they'd thrown in the documentation for the newer ANT+ models despite the fact it specifically said 2.4 SL and there was another download for the SL+ listed.
The again, after talking to their support department, this doesn't surprise me.
