Calibration ride gives positive tilt value

[tombishop]

Hi,

I've been following some of the posts about getting a more accurate set of data with interest. It seems that using the factory settings get reasonable results for most people, but if you are willing to put some effort in, you can get more accuracy. I am definitely in that second group!

My initial findings were that the power readings were reasonable on uphill gradients and the flat, but on fast downhill sections were under reading. For example, during a steady downhill with a steady state heart rate gave much lower readings that the same steady state heart rate uphill.

After some false starts, I decided to do an out and back calibration ride, having forced the wind scaling to 1.4 as I am using the standard mount on the handlebars. However, when I run the calibration check in Isaac it recommends a positive tilt value (and negative friction) with wind scaling of approx 1.1. The negative friction value means that profile cannot be loaded to the power pod!

I'd be grateful for any insight into what to do. Is my out and calibration ride unsuitable? In the UK we have a lot of hedgerows which can result in fairly unstable wind conditions. The calibration ride is attached.

Thanks for your support

Tom

[tombishop]

Also the original profile for my out and back ride, wind scaling was 1.3 not 1.4.

After analysis, Isaac recommends wind scaling of 1.1 and positive tilt

[Velocomp]

Please do a short out and back ride with your new profile, then post it.

Positive tilt is not an issue.

[tombishop]

Hi, I cannot load the profile onto the power pod as it says that a negative friction value is not permitted. Maybe that should have been my post title!

Tom

[Velocomp]

OK, load the attached factory profile into your PowerPod, then do a new pairing and 5 minute ride.

[tombishop]

Ok, I have redone the calibration, and following that did an out and back ride.

After analysing the out and back ride, this time I get a wind scaling number of 1.236. This seems quite low compared to 1.4 and I'm concerned this will result in low power readings on downhill.

Does my out and back ride look reasonable?

Thanks for your support with this.

Tom

tom bishop profile before out back.ibp

(378 Bytes) Downloaded 169 times

tom bishop profile after out back.ibp

(518 Bytes) Downloaded 179 times

iBike_05_03_2016_1933_5_Miles_cal.ibr

(67.07 KiB) Downloaded 183 times

[Velocomp]

What the out-and-back cal ride does is determine PRECISELY the air resistance for the exact location where the meter is placed. There can be minor differences and the cal ride dials things in exactly.

Everything looks fine and, actually, the factory default number of 1.4 is very close for you!

If you customize your profile using 1.236 (the result from the cal ride), accuracy will be even better, but it only makes about 10W difference.

I use the factory setting on my bike. I know I could get a bit more accuracy if I did the cal ride, but for me consistency is more important than absolute accuracy.

[tombishop]

I thought I should report back after updating my settings - I am grateful for the support.

Things seem quite reasonable now so I am happy. But it has made for some interesting observations about physiology and psychology when riding with power measurements!

I find that as the road slopes up, it's easy to hit high power as you try and maintain speed - not so good for a recovery ride. But now I can see this happening more quickly than with heart rate.

Equivalently, as the road slopes down I find it harder to keep the power high. I think this is partly because the downhill normally comes after the uphill, and I have already been working quite hard. My heart rate seems to not change even though power drops, but this is probably because I am still recovering from the uphill. Also as gravity accelerates you, you have to keep changing up through the gears to keep the load on the pedals.

It's all very interesting!

Tom

[Velocomp]

True enough...pay attention to the "Normalized Power" stat in Isaac. NP is a better metric of physical effort than average power, particularly when you are doing uneven levels of work.