Erratic power data

[GordonCampbell]

Hi,

I got my powered this week and have done my calibration ride. During a couple of rides since, the power reading is very erratic. The reading goes to zero or to very high readings.

Im using the new garmin magnetless sensor on the front wheel and its mounted on a tt bike (on the bars). Ive attached a picture along with a ride file.

Any thoughts?

Regards,

Gordon

[Velocomp]

I see at least two problems:

1) PP is positioned out at the end of the aero bars, where vibration effects are amplified

2) It looks like PP is attached to the aero bars with a plastic mount, further adding to vibration

You need a very stiff TT mount, such as the one we make. Also, the TT mount needs to be attached as close as possible to the handlebars. Do these things and you'll get good results.

[nicholp1]

hi Gordon

Just a word of warning The TT mount that Velocomp make won't fit on those planet X tri Bar extensions because of the reduced diameter of the extension where they fit into the base bar. I would have thought your best option would be to use the standard PowerPod mount on the base bar, it looks like there might be just enough room to fit it in between the stem and the round section of the base bar.

Your tri bar setup fortunately looks quite wide so hopefully you should get a good clean airflow to the.

Best Regards

Peter

[Velocomp]

hi Gordon

Just a word of warning The TT mount that Velocomp make won't fit on those planet X tri Bar extensions because of the reduced diameter of the extension where they fit into the base bar. I would have thought your best option would be to use the standard PowerPod mount on the base bar, it looks like there might be just enough room to fit it in between the stem and the round section of the base bar.

Your tri bar setup fortunately looks quite wide so hopefully you should get a good clean airflow to the.

Best Regards

Peter

Peter: could you provide more information on the planet x tri bar extensions? The PowerPod TT mount fits aero bars with diameters of about ¾ inch

[nicholp1]

Sure

here is a link to the Planet X website

http://www.planetx.co.uk/i/q/HBPXSBEX/p ... &#Acomment and close up of the extensions.



As you can see, one of the bar is standard width 24mm, the other end where it fits into the base bar is considerably less. I don't have a measurement for it, but I would say about 13mm (1/2")

Regards

Pete

[Velocomp]

I suspect our TT mount will work with these aero bars, but it is going to be really important to attach the TT mount as close as possible to the point where the aerobars attach to the handlebar and stem. This is the point of minimum flex of the handlebars. When PowerPod is attached far away from the stem flex and vibration can become an issue.

[Velocomp]

Peter has been very helpful with some images of these aero bars.

Judging from their appearance, they have (sigh) made a non-standard, very skinny attachment point to the main handlebars.

Our TT mount is designed for standard 24mm aero bars.

Also, because of the very skinny size of the aero bars, these will be prone to flexing and vibration. Mounting PowerPod far away from the stem will cause big problems.

PowerPod definitely needs to be attached close to the stem!

There are three possible options:

1) find a hard rubber adapter ring that will thicken the aero bars to 24mm and allow the TT mount to be fastened very near the stem

2) If there is sufficient space, attach the standard PP handlebar mount to the small gap between the stem and the thick portion of the aero handlebars

3) If possible, attach PP to the very short handlebar extensions at the end of the handlebars

This is as frustrating for us as it is for you; as soon as we make an "industry standard" mount, someone dreams up a non-standard configuration!

[GordonCampbell]

Pete, John,

Thanks a lot for the feedback. Ive managed to mount the supplied clamp right next to the stem as suggested, did another calibration ride and then a short 10km test ride. Data seems to be better but I've attached the ride file and photo of new mount. I stupidly didn't do an out and back.

Pete, you have a good eye! the narrow part of the tri bars is 16mm dia!

Any other comments on settings etc would be greatly appreciated.

I will need to find a new solution to my profile design TT water bottle though! :-0 Unless you think its far enough away at 50mm (2")

Gordon

[Velocomp]

This looks MUCH better.

Since you have an out-and-back, you can use the command "Analyze/Check Calibration..." to dial-in your profile.

Also, you have a TT bike, so I adjusted the CdA to about 0.28

I've attached correct profile and ride file.

Import the profile using the Edit/Edit Profiles command, then send it to your PowerPod with the "Send to Device" button in Edit Profiles.

You can do a ride with your water bottle, then post a ride file.

[GordonCampbell]

Hi John,

Thanks again for getting back to me. Ive uploaded the new profile (made a wee change to the bike and rider weight to 82kg combined).

Ive done another out and back x2. First shorter one of 2.5k was with the water bottle attached. The next 8km was without. With the bottle attached, the garmin edge display was showing zero watts a lot and a much lower average than after with the bottle removed. Both rides on the PP are on the same file. ( i didn't think to turn it off and on again! ) but on Garmin i started a new ride. First one is 53W ave and the second is 153W. I think that answers my question about the water bottle. - can't have it!

Looking at the ride from 5km till the end, do you think the calibration looks alright now?

Regards,

Gordon

[Velocomp]

We can adjust your profile so that it will work with your water bottle. Would you like that?

[GordonCampbell]

Sounds interesting? If you can send me a trial profile then that would be great!

Out of interest, how can that work if its blocking the airflow to the PP - or blocking it from one side if its a cross wind? - Very intriguing!.

FYI, I've attached 2 x 50mile rides from today in case that helps.

Many thanks,


Gordon

[Velocomp]

Were the two rides you attached done with the water bottle on your bike?

[GordonCampbell]

No. I didn't have the bottle attached as i wanted to see the power data. It looks a bit lower than i expected though.

[Velocomp]

I think your data is just fine for the two rides. When you do a ride with the water bottle please post that one so we can compare.