Power variance - out front mount vs handle bar mount

[Bugsbunny]

Hi there John,

I'm just fine tuning my PowerPod.

I started with the handlebar mount and had it working well there. Ridden it about 12 times without issues. Wind scaling at default 1.4.

I've since bought the front mount in the hope that this would help me get more accurate readings.

Now, what I found was with the out front mount, my the power readings seemed to be much lower than my perceived power output vs the stem mount. It seemed in the vicinity of about 30 watt delta.

The wind scaling is 1.7.

I'm riding the same road and the conditions are largely the same.

Any thoughts on the differences between out front vs handlebar mount?

[speedracer]

You need to do an out-and-back ride to get this more accurate.
Even on the same mounting position on different bikes the wind scaling value varies.

[Bugsbunny]

Thanks Speedracer

How do I do an out and back?

Do I redo the 5 minute calibration and ride 2.5 min out and then 2.5 min back?

Bugs

[speedracer]

No, you start a new ride. Then you go for a 5 minutes or a bit more (not too long bcs. of changing wind conditions) ride with in best case no traffic and after 5 minutes you go back the exactly same way and stop the ride. Then download the file with ISAAC and choose the calibration check option for this ride.

Then you will receive the values which you need to change. In my case it worked on all three bikes perfectly. You can see the results here: http://ibikeforum.com/viewtopic.php?f=93&t=3524#p19252

Even 1.7 was recommended the Watts were a bit too high as I found and the out-and-back said the same:



After changing everything looks perfectly.

[nicholp1]

Welcome to to the "out and back ride Club" . I'm sure John will wade in here but the only real way to get consistency between the two mount positions would be to do a out and back calibration ride on each to establish a base line for comparison.

What I'm sure you are finding is that you get replicable numbers ride to ride with the PowerPod whilst in one position (mount) use a factory set bike profile. The Wind Scaling values of 1.4 ( bar mount ) and the 1.7 ( out front ) are factory set default values and my well differ slightly based on your situation (position of unit, your size, weight).

If you want to get the two mount positions line up you would need to do a "out and back" with the power pod in one position and then run a check calibration in Issac to get suggested set of vales. You would then need to setup the PowerPod up on the new mount and do a "out and back" and then run a check calibration. Only then would you have a equal base line between the two mounts. I think I'm correct is saying Issac let you apply a profile retrospectively to a ride file, so if you we so inclined to do so you could adjust your historic ride files based on your new profile for the original mount.

Given the amount of "faffing around" it would take to achieve this, I'd suggest you stick with your new mount, do a "out and back calibration" and keep with those values going forward.

[Velocomp]

Watch out, nicholp1, your answer is so clear and so correct that you may be recruited as a tech support person...

[nicholp1]

Thanks John, it's been said before "we are all learning so much here" and it's good to help each other out. Having said that a quick reply here provides a suitable distraction during a dull financial forecast meeting..

[Bugsbunny]

No, you start a new ride. Then you go for a 5 minutes or a bit more (not too long bcs. of changing wind conditions) ride with in best case no traffic and after 5 minutes you go back the exactly same way and stop the ride. Then download the file with ISAAC and choose the calibration check option for this ride.

Then you will receive the values which you need to change. In my case it worked on all three bikes perfectly. You can see the results here: http://ibikeforum.com/viewtopic.php?f=93&t=3524#p19252

Even 1.7 was recommended the Watts were a bit too high as I found and the out-and-back said the same:



After changing everything looks perfectly.

Thanks so much guys. I'm slowly becoming more comfortable with the PP and ISAAC.

Few dummy questions.

Question 1
How do I STOP the ride so the out and back is "equal"? I know to start PP - I just click the button (green) and ride. But when I want to stop it, do I physically stop the bike from moving? As my start and end points is a little walk from home as I want a clear road. I'm assuming to stop, I get off the bike and carry it so there is no further movement of the cadence/speed sensor.

Question 2
Looking at the picture you embedded under "Check Calibration", do I click "ACCEPT" and "SEND PROFILE TO IBIKE" - and this basically updates the profile and thats it?

Thanks to all...

[Velocomp]

Thanks so much guys. I'm slowly becoming more comfortable with the PP and ISAAC.

Few dummy questions.

Question 1
How do I STOP the ride so the out and back is "equal"? I know to start PP - I just click the button (green) and ride. But when I want to stop it, do I physically stop the bike from moving? As my start and end points is a little walk from home as I want a clear road. I'm assuming to stop, I get off the bike and carry it so there is no further movement of the cadence/speed sensor.

Question 2
Looking at the picture you embedded under "Check Calibration", do I click "ACCEPT" and "SEND PROFILE TO IBIKE" - and this basically updates the profile and thats it?

Thanks to all...

Q1: You can certainly stop the ride the way you are suggesting

Q2: You click "Send PROFILE to iBike", then click the accept button.

[Bugsbunny]

Hi John

I'm getting really confused. I'm doing all sorts of things and are getting "lost".

Is there someway to completely and utterly reset everything and start again? I'm lost as I've already done the calibration - and now resetting it for the new front mount. But now, somehow I've got it calibrating again. And things have not improved. I've just come back with an average power of 68W which doesn't sound right.

Also when I set it to profile 2, and I select "front mount" to where its mounted, it never seems to register that choice.

And why does it default to wind scaling 1.5 for profile 2 when it should be 1.7?

I need help to set it up and once done - I'm not intending to touch it again.