AeroPod, PowerPod and Newton

Let me just start by saying, thank you for being very patient with me and my questions.

My current set up (tilt, wind, cal etc.) are all following the set up steps that came with the Newton and I not knowing what determines riding tilt, I am admittedly lost as to how it came about. For reference, my two bikes have either -.7 or -.8 tilts, my old gen 3 had -.5 and -.6.

Maybe a discussion offline may help lessen the back and forth?

Fernando,

Can you explain a bit about wind scaling I see that you have mentioned it in several of your replies in regards to calibration issues. I understand both the rolling resistance and drag and how they play a part in the wattage calculation; but just what is wind scaling and what roll does it play in the overall picture?

Thanks in advance,
Kim

"Wind scaling" is a calibration factor applied to the air speed/ dynamic forward pressure sensor. For instance even if your unit is zeroed properly, it may indicate a relative wind speed of +10mph when it is really 12mph. The "wind scaling" factor compensates for this.

jslopez93 wrote:Newton and I not knowing what determines riding tilt, I am admittedly lost as to how it came about. For reference, my two bikes have either -.7 or -.8 tilts, my old gen 3 had -.5 and -.6.

Assuming that both of these are accurate, the riding tilt can be effected by vibration on the road you used for calibration. More likely that tiny difference is just a small cal error. It isn't very important though, since the iBike sets the tilt based on elevation data after 5 minutes of riding. No matter how bad your riding tilt is screwed up, it will automatically be fixed after 5 minutes.

rruff wrote:"Wind scaling" is a calibration factor applied to the air speed/ dynamic forward pressure sensor. For instance even if your unit is zeroed properly, it may indicate a relative wind speed of +10mph when it is really 12mph. The "wind scaling" factor compensates for this.

So using the above example would the wind scaling be .83 or 1.2? Secondly should this number change from time to time during the riding season; or is this a constant that once the Newton+ is calibrated should never change?

I don't recall for sure... but I think the wind scaling would be 1.2^2 in that case or 1.44. It is a scaling on the dynamic pressure reading, which is proportional to V^2.

It should not be something that changes with time... provided that your position does not change significantly, and the position of the iBike does not change.

"It should not be something that changes with time... provided that your position does not change significantly, and the position of the iBike does not change."

While that may be true in theory, I have had mine change a few times over the last few years. Same bikes, same rider, same everything. No idea why it changes or what actually does change but I can always tell when my numbers seem "off" from what I would expect. I test it against a PT and sure enough, there is a change.
Actually this happened to me just last week with my Newton. The WS went from about 1.37 (which was providing outstanding results) to where it is now at about 1.64. Again, the results are right back where they should be, compared to the PT, but the WS did change.
As Fernando has pointed out, they are simply numbers. What they are shouldn't matter just that you get it right.

Please post ride files.

Wind scaling needs to be very accurate for you to be able to then make sure cda is right. With my Newton my first 2 cal rides gave wind scaling of around .740 but something seemed off so a couple days later I did 2 more and ended up with .809 and .811, then today did 2 more and ended up with .909 and .914. Based on my numbers on the coast down screen while going downhill at >30 mph with my cda at .350, the .900 ones are to high, and the .800 are to low so after doing a out and back ride the software told me to change my profile to .836 which I believe finally seems like I might be getting really close. And to be honest thats all I want is to be close not exact..just close. So just wanted you to know that wind scaling must be good for everything else to fall into place.

Just a note... your downhill readings can be effected quite a lot by small tilt errors, so it isn't the best way to check wind scaling. The best way is with several out and back rides... no traffic, preferably light wind, make sure the wind offset is zeroed.

So small tilt errors can cause numbers to be off in the coast screen?? So far every time I use the check cal screen my tilt stays right at -0.7. I have noticed that if I put air in my tires (which I should do every ride, but don't always) up to 120lbs my tilt changes to -0.8.

By several out and backs do you mean over a period of days or do them all at the same time to maximize the current conditions so you get consistent results? If doing them all at once do you just ride back and forth multiple times like 4,5, or 6 times or do you do a trip reset after doing each one and do it again, then figure out the average wind scaling? Just curious. I have done a few out and backs the last couple of days and my scaling seems to be consistently around .840. This is lower than my last cal ride ride on a bike path that was at .914 so I changed to the lower number.

I started to type this a couple hours ago but got pulled in other directions.

Let's try and put the wind calride to bed. Only one good calride is needed to establish a good tilt offset and wind scaling. It needs to be a two mile ride, one out and one back. Ideally no traffic, little or no wind if at all possible. This will easily establish good numbers.

If you want to do two or three cal rides and take the average of the three, that fine but do them all under the same conditions. Back to back. Reset the ride between each one so the Check Calibration feature of Isaac works. Unless you get an outlier that clearly doesn't fit, just take the average of the calrides and create your own profile.

You can also do longer calrides, however the longer the calride the better the chances of anything changing and skewing numbers.

It is important to note that all that is needed is one good calride in order to complete a setup. Everything else is just a bit of confidence building.

Ok after looking at my cal ride files it appears that my wind scaling would be around .909-.923. However after doing some regular out and back rides and then doing chek cal it says it should be around .836-.861. So do I use the cal ride number or the check cal numbers?

After getting this right which I now am very close how does one go about checking to make sure cda is right?

Thanks

GWPOS wrote:By several out and backs do you mean over a period of days or do them all at the same time to maximize the current conditions so you get consistent results? If doing them all at once do you just ride back and forth multiple times like 4,5, or 6 times or do you do a trip reset after doing each one and do it again, then figure out the average wind scaling? Just curious. I have done a few out and backs the last couple of days and my scaling seems to be consistently around .840. This is lower than my last cal ride ride on a bike path that was at .914 so I changed to the lower number.

IMO it is best to do a bunch of out-back rides. With no wind, and no traffic, you should see zero net wind on an out and back, if your setup is accurate. Wind always fluctuates a little though, so it's best to average a bunch of readings. Plus it is good to check the results on windy days too, although in that case you would not expect the net to be zero... a stiff crosswind should result in a net wind of 1mph or so.

You don't need to do a cal ride to check this. Just highlight the section where you did your out-backs in the software and see what the net wind is.

Ok I now feel confident about my wind scaling. It is about .914ish. It goes down to around .850ish give or take if I ride in traffic.
So now on to my next question.....how about verifying my cda. is correct. I am still getting high neg. numbers in coast screen at 25+ mph coasting downhill. Is this still a valid way to check cda??

Using the coastdown screen works, however upwards of 25mph the numbers tend to skew. So if you're showing slightly negative that will tend to amplify. If you're going to look at coastdown numbers do so at about your average riding speed which is generally under 20mph.

This is one of the reasons I like the live CdA screen, it doesn't jump around as much. I have my CdA set at .368 and after yesterdays intervals I did some coasting from 20 to 15 mph. I got .37 twice and .38 once. That's good enough for me.

Racerfern. Thanks for your input once again. As for the cda screen I have the Newton, not he plus "+", so I was wandering how I should do it. So I should do it at normal riding speeds. I remember reading a post that said it should be done at >30mph so that is why I was re-asking the question on how to go about verifying my personal CdA.

Over 30mph the numbers get skewed and tend to bounce quite a bit. I go down some big hills and can confirm this. The slightest twitch makes it difficult to nail down. I like doing the coastdown screen check in the 20ish mph range down to 15, but certainly not much over 25 unless you regularly average 25-30 mph on rides.

I was noticing that to on steep hills. The numbers were all over, especially if I "twitched" as you put it. I think I am close so I will try it at a lower speed and see what happens. I know it should be in the .350-.371 range from everything I have read. I also know that small of a difference will not change power numbers while climbing, but on descents and even a little on the flats is where I want to be closer on.

A method I sometimes use, which I posted once awhile back and it was poopood a bit, but seems to work well for me is:

Soft pedal on a smooth downhill road, a longish one that will hold your speed up to say 25mph or so. Hopefully this is a no wind or steady wind day with no traffic. Actually a head wind is good for cda, a tail wind is good for crr checking.

Ideally your crr is dialed for that road. Of course you need a good wind offset and wind cal for this to be any good too.

Now in iBike software or Isaac, with the ride uploaded, zoom in on the soft pedal section.

Tweek the crr/cda values as need to just see the lowest amount of power with flattish sections of the power curve, sometimes there are peaks or humps.

Next tweek your cda down one value so it shows zero power and that should be correct.

The same process can apply for crr, especially if you had a stiff steady tailwind !

As I said, it seem that it Works for me.

Russ