Watt numbers completely wrong!

[oestergreen]

Having used my iBike iSport for about a month with watt numbers being fairly consistent, things have lately changed.

Every time I do a new ride on the road, my iBike starts out with watt numbers being completely wrong. Often my iBike is showing watt numbers around 1.000 og 2.000 (one or two thousand!) though I am just warming up with very little effort. Then after a few minutes the numbers start dropping. After 5 minutes my iBike might show about 700-800 watts, and after 10 minutes about 300-400 watts. After 15 minutes the number might have dropped to below 200 watts. This number might be close to my real effort (still warming up), but if I then do an interval going for full power, my iBike might rise to 300-400 watt and then quickly drop to 100-200 even though I am working very, very hard (which is usually AT LEAST about 300 watts for me). The other day I did a test ride for 25 minutes giving all I had (which is normally about 350 watts for this period of time) but at the end of the ride my iBike showed less than 200 watts on average!

I have followed the instructions in the manual very closely, doing a calibration ride as a fundamental step. Before every ride I am waiting about 5 minutes for my iBike to acclimate outdoors, and after waking up my iBike I wait for it to do an automatic wind calibration with no wind hitting my iBike. I have also inserted new batteries in my iBike. I have not done any coast downs, as these should not be necessary.

Unfortunately I can not upload any iBike files for analysis, as this is not possible with the iSport.

Any help/ideas would be very much appreciated!

[Velocomp]

Your tilt calibration is incorrect. This leads to wacky watts numbers for the first 5-10 minutes.

To prove this, after letting your iBike sleep overnight, put it on your bike and wake it up. Then, click the down arrow once so that slope is showing in the top screen. On a reasonably level surface you'll see a large, positive hill slope in the top window, indicating that your tilt cal is incorrect.

Do a new tilt cal and things should be OK.

[KenS]

I've also got the iSport on 4.25 and mounted on the rechargaeble mount so its pretty solid. I have also been having problems with wattage in the first 5 minutes although it seems to be inconsistent. So a couple of days ago I did a tilt cal before my ride and all was well.
The following day I put on the iBike and woke it up. On flat ground it was showing near to 0% grade so all seemed well. Then as I rolled out onto the road and down the 8% hill it suddenly shot up to over 20% UPHILL. It stayed that way for over 10 minutes then sorted itself out. Other times it has always come good after 5 minutes.
Then today I put on the iBike, woke it up, checked the grade and once again it was showing close to 0%. This time I rolled out onto the road but went up the hill and everything seemed fine. The power readings were a bit funny but we had a very strong gusty wind which was probably contributing.
I'm interested to know what the variables are in the 5 minute adjustment period. Among the things I'm wondering are:
When does the 5 minutes start. If I wake up the iBike with the bike on a tilt and leave it that way for a few minutes will it "autoadjust" unnecessarily or does it wait till I start moving? Does the altitude reading affect things? Should I do a trip reset first? If I know what the variables are I can try some controlled experiments to get to the bottom of it.
It's not highly critical for me - I just like having clean data. I'm getting into the habit of doing a trip reset once the numbers settle so I get a reasonable NP, IF and TSS. But I also record the power readings on my Garmin and it picks up all the bad stuff.

[Velocomp]

Your internal "Riding Tilt" number is incorrect.

To get things right do the following:

1) Perform a tilt cal and wind cal

2) Immediately thereafter do a Cal Ride

This should fix things.

[KenS]

I think I'm getting to the bottom of this.
Did the tilt cal, wind cal and cal ride but I was still having problems at he start of some rides.

One thing that seems to work is as follows:
As soon as I switch on the iSport I do a trip reset.
I then set the altitude to the right value.
If I do that it gives good readings right away.

I suspect something to do with changes in the barometer from one day to the next. So when I get home my altitude is 75 metres. But if the barometer falls then the next day before I start riding I might see 125 metres. Or if it rises then it might read 40 metres. So it looks like the iSport thinks I've had a sudden loss or gain in altitude and takes the first 5 minutes to sort it out.

But if I reset and set the altitude this seems to give it the right starting point
Does this sound plausible?

[lorduintah]

At the end of your rides -- are you doing a trip reset? That is where it should be required. It is possible that the reset right before a ride is a direct result of the previous comment.

[KenS]

I'm not very consistent about resetting at the end of the ride. I always reset the Garmin because I download the data right away but since I don't download from the iSport I sometimes forget.
I'll start to reset after each ride and see what happens.
Thanks for the advice !