V4 calibration results - Coastdowns

[coachboyd]

There can be a really big difference in wind scaling between the handlebar mount and stem mount. This will be shown with a different aero number as well to get the same cda number. When you do a coastdown you get an aero and friction number, this is what the iBike reads to get power numbers.

The wind scaling is the number that calibrates the wind port (and the wind speed readings). When you know for sure the wind speed readings then you can get cda from the aero number.

Changes in angle of the unit, position of the unit, or just different units can have a different wind scaling. This will make the aero number different (and also to where it will really change the data if you use "switch profile after the ride" to a profile with a different wind scaling)

[wellmt]

Bex. John Hamann has asked me to do a couple of tests, which I will try and do tonight (weather permitting).

[bex]

What are the tests?

Bex

[wellmt]

I've got to go and do two cal rides. One the new V4 length (1 mile) and then straight after, a 2 mile cal ride. I believe John thinks that a longer cal ride might help obtain a more accurate CRR. I won't be using the estimated CRR feature, but a CRR obtained during the coast downs. Basically I'll be doing a V3 style calibration!

Using the adjusted option in the software, CDAs before and after the V4 upgrade are both .36x, which is great (although in my initial post it was lower). Basically, it's when I try and peg the CRR at what I've we've been told are normal values that the weird values start occurring. It's the fact the manual suggests pegging the CRR should give a more accurate CDA which is the confusing issue.

I can honestly say that I'm a bit fed up of cal rides but I'd like to help figure this problem out if I can.

[lorduintah]

FWIW - I don't think you are required to do just a 1 mile out and 1 mile back with V4. So for others reading this topic, you might consider a 2 out 2 back if you are having similar issues...

TOM

[wellmt]

Yes, you can actually go as far as you like for a cal ride before turning around and ride back. The new firmware will tell you to turn around after a mile but you can ignore it.

[bex]

But presumably when going more than 1 mile out you should not fall below the 8mph limit? I ask this because, again presumably, the ibike will view this as the turnaround? Or does it not operate like that?

Bex

[bex]

By the way, how is the wind port calibrated. What causes the wind scaling to be one number or another?
Which aspect of set up is the wind scaling calibration.
Perhaps if I got that info I would be closer to understanding why I am not achieving consistent, repeatable results for obtaining a profile that works for me.
As I have said, mine has never been lower than 1.2something or other and that apparently is a tad high. why?

Bex

[wellmt]

The wind scaling is determined by the out and back cal ride. This is why ideally you need to do this in calm conditions, straightish road with no traffic. Yeah I know it's not something that exists in the UK . Yes you can go as far as you want but don't drop below 8mph like you say.

For example I did my tests for John tonight even though it's a bit windy. As a result my wind scaling was a little bit low.

The good news after the tests is:

I did two cal rides long and short, back to back with a wind/tilt cal inbetween. I then proceeded to do a dozen coast downs using EST FRIC: NO (i.e. make the iBike calculate the CRR from the coast downs).

The old school cal ride of 4 miles (2 out, 2 back) gives a sensible CRR of .0040 which is believable and CDA of .376
Using the V4 suggested 2 mile ( 1 out, 1 back) method does not give a realistic result (the CRR is calculated to be .0020) and CDA of .361

So at this moment, it looks like longer cal rides are the way forward. As John says, more data is better.

[bex]

Do you mean your wind scaling was a little bit high, not low?
What was it?
I analysed my last out/back, the one with the 1.279 wind scaling and had an avg ground wind of .5MPH.
I am not sure I could get a better condition than that.
Boyd has suggested a similar procedure to what you have done but I am waiting for a confirmation of a couple of things I am confused about.
This is what he wrote:
When doing a profile it’s best to run through all the steps (wind offset, tilt calibration, cal ride, coastdowns). Then when you get home send the profile to your iBike and then erase all ride data.
The he wrote this:
In the new profile if you go into the racer submenu you can set a fixed crr. If you are doing coastdowns on good tires on a smooth road I recommend changing that number to .0045 and then afterwards in the profile adjust the friction number until the crr changes to .0055.

I am not sure if the second para above is to be carried out before I do the first part. That is what I am waiting to find out. Its way too windy today/tonight to be going out for coast downs so I am just trying to sift through the forum for more info and wait for a reply from the Coach.

[wellmt]

It was .787 as opposed to a little bit higher (.8xx)

Looking back over previous profiles, actually it may be OK. Average ground wind on long cal ride was .6

Ah I see what Coach does. I think you'd tweak after you've got your profile.

[rruff]

So at this moment, it looks like longer cal rides are the way forward. As John says, more data is better.

If you are trying to isolate WS, then the best procedure would be to many out-back trips over a short course. This way any variations in wind speed will average out, and you can also easily see what the variation is between "laps". If you can ride in the same part of the road in each direction and also avoid traffic completely, it is even better.