Tilt Calibration results

[Ratman]

Yes, Tom, I seem to be seeing the same behavior. I do meticulous tilt and wind offset calibration pre-ride, but see fairly large tilt errors upon downloading to the iBike 2 software (today was +20 watts average on a 55-minute ride). I think this has been more noticeable since upgrading to the iAero, even with a "rock-solid" mount and no software-identified "drop-outs."

I, too, am curious to know what, if anything, can be done to get better on-bike results.

[smokey26_02]

Well am on the same boat.

Most of my days my ibike will avg on the road about 30-40 watts less then when I download it into the software and analyze it. What I do while am hammering is just add 30-40 watts to the measurement I am seeing and thats how I pace myself so that I dont blow up.

One day it was like 60+ watts which was shocking to me. But for the most part my avg power for the ride after using the software to analyze it, I am getting a 30-40 watts jump on my avg once i do the software analysis.

Freddy

[rruff]

Just wondering... do you know that putting weight on the bars will cause the iBike to tilt downhill slightly? So if you did the tilt cal with the bike unweighted, the iBike thinks you always have a downward slope that is greater than it really is... resulting in lower power numbers. I think the software has a way of correcting for this, but I'm just guessing.

[coachboyd]

The amount of tilt caused by putting your hands on the bars and etc is the riding tilt as seen in your profile. I know for me it's -.139% That's how much my bars, tires, fork, and such flex in my normal riding position. This number is generated when you do your coastdowns and 4 mile out and back ride. If you are always having large corrections post ride, I would recommend redoing your profile.

For myself, on a 50 mile ride, I usually only have about 40-50 feet of elevation discrepancy. This throws off my average watts by about 2-3 watts, so I know the wattage on the screen is the actual wattage I am putting out.

(unless I decide to ride a lot of wheelies)

[coachboyd]

I'll show you what I mean. This is a screenshot from one of my teammates. His riding tilt was off and after I saw this I told him to redo his profile

Notice how much the watts changed before and after, and he had performed a tilt calibration just prior to the ride.

As opposed to one of my rides, which actually looks worse at first, until you see the scale. Notice how the average and max watts barely change in the before and after. And the big jump that you see at mile 30 is when the race was over and I left my bike sitting in the sun for a while, then hopped back on it.

[travispape]

There have been several questions coming up recently regarding tilt and riding tilt, and I thought I would try to give as brief of a summary as I can about the important points to remember regarding tilt.

Tilt calibration is done from the setup screen on the unit itself. The recommended method is to do it off the bike, but if you decide to do it on the bike, you must always do your tilt calibrations while on the bike. Again, it would be better to do this while off the bike in order to be as repeatable about it as you can. Also, don't be in a hurry--be still. Keep the bike fully upright near its balance point. The accelerometer is sensitive enough to pick up the minor movements of the bike.

Yes it is true that when you get on the bike, the tilt of the unit will change due to your body weight. This is called the riding tilt, and it is ok to have some riding tilt. The fric coefficient takes into account both the rolling resistance and the riding tilt in the firmware power calculations--this is why you don't need to worry about being on the bike to do your tilt cal.

(It is hardly worth mentioning, but it is true that the slope measurements you see on the unit while riding will under-report slope by the amount of your riding tilt. Again, this does not cause an error for the power reported on the road. Once the profile has been attached to the ride file in iBike2, the slope numbers will be adjusted.)

Riding tilt is measured on the day that you do your coastdowns and 4 mi ride. Depending on several factors including rider weight and bike stiffness, it can be close to zero or -1% or even more negative. Due to this riding tilt, you would expect to see the corrected and uncorrected tilt lines diverge in the window for processing calibration rides. The following screenshot shows a good measurement of riding tilt.

good 4mi ride.png (45.82 KiB) Viewed 7933 times

On a daily basis when you download your ride files, the riding tilt is removed from the slope data as soon as you do something that causes the profile to be attached, usually either pressing the Auto Analyze button or selecting the Detailed tab page.

When you select the detailed tab and press the "Analyze Tilt & Power..." button and then press the "Advanced..." button, the graph that you see on the top is after the riding tilt has been removed. Ideally, the green line in the top graph is already close to 0 slope; however, in general there will still be some tilt error and the graph on the bottom shows the result after removing it.

Boyd's screenshot earlier in the thread for his own ride shows a good example of everything working well. Like he pointed out, the vertical scale is "zoomed in"--the magnitude of the numbers show little tilt error.

There are a couple of things that might have gone wrong for his teammate's ride in the other screenshot Boyd posted. The tilt calibration might have been bad on the day he did his calibration rides, or on the day of the ride, or both. If for day after day, the teammate sees the same behavior of the green line, that is a strong indication that the riding tilt saved in his profile is bad. In contrast, if the tilt error behavior is different day to day (but always bad from the beginning of the ride), that would probably be an indication that the rider isn't doing good tilt calibrations before some rides. Again, when doing the tilt cal don't be rushed, hold still, be balanced, keep the handlebars steered straight forward, don't be buffeted by the wind, be sure to get the wheels on the exact same spots when you tun the bike 180 degrees.

If you see the slope make a change during the course of a ride, like in the attachment below (and to a lessor extent in Boyd's good ride), that is an indication that the iBike unit or its mount is physically tilting slightly during the course of the ride. In the screenshot attached below, it happened suddenly at roughly mile 6. In Boyd's good ride, you can see the slope change in several places, but all of them are small. They also happen to cancel each other mostly for the total ride. If you consistently see the slope of the green line changing mid-ride like in the screenshot below, that is a good indication that you need to work on making a the mount more stable. The slight changes in Boyd's ride are par for the course and likely nothing to worry about.

slope change.png (46.89 KiB) Viewed 7932 times

Keep in mind that it only takes a small amount of mount shift to show up as a tilt error. For numbers, say that the double-stick tape between the mount and the bars squishes in a wedge-like fashion by only 0.004", which is the thickness of a piece of 20lb paper. Given the 1.25" width of the mount, this results in a 0.32% tilt error and would create a very visible change in the slope of the green line. There are any number of places in the bike that might "creak" a little and cause slight tilt errors that can be detected by the tilt error. Given the hand-numbing vibrations that a bike experiences on the road, it is to be expected that you will sometimes get actual small changes in slope of the iBike unit.

Travis

[luv2climb]

I did not want to start a new thread on this as my question directly relates to this subject.

I have the continually upward slopping green line in the tilt screen for all my rides. I realize that my 4 mile ride was not perfect as a result and I will be re-doing my coast downs and 4 mile ride. In the meantime Fernando has walked me through how to correct this so that in iBike 2 corrects it once downloaded.

However, if I take this adjusted profile that contains the new Riding Tilt % and send it to the iAero will it fix it in the short tem? I ask becuase I tried this but my green line is still the same. Or are these values ONLY changed when you redo the CD and 4mr and then accept the profile, and send it to the unit?

[rruff]

However, if I take this adjusted profile that contains the new Riding Tilt % and send it to the iAero will it fix it in the short tem? I ask becuase I tried this but my green line is still the same.

If you save the profile and send it to the iBike, then it is changed.

Are you talking about a green line from a ride *after* you changed the profile? If so, then you probably didn't correct the tilt enough.

[racerfern]

rruff is correct. You probably did not make enough of a correction. Send your corrected profile to the iAero for a quick fix until you do another set of CDs and 4OB

Also, if you make an adjustment to profile just click "Switch to this profile" after the fact and check your tilt and power analysis tab.

[luv2climb]

Thanks both of you. I think maybe when I was tweaking it I tweaked it the wrong way and made it worse!

I am still learning about all this as I have only had my iAero a week. I am planning on doing another set of CD's and 4m tomorrow. I went out to do them today and it was kinda windy. I want to get the best I can so I bailed on it today.

[travispape]

Thanks both of you. I think maybe when I was tweaking it I tweaked it the wrong way and made it worse!

If the trend on your top green line is that it usually points down after most of your rides, then you need to decrease the riding tilt, which usually means making it more negative. For example, if you find that after post-processing your ride files with the "analyze tilt and power..." button that your average slope increases by 0.2 percentage points, then decrease your riding tilt from, say, -0.4% to -0.6%.

{Edit: Fernando emailed me that I had gotten that backwards myself. I just fixed it.}

And visa versa if the trend is a top green line going up.

I am still learning about all this as I have only had my iAero a week. I am planning on doing another set of CD's and 4m tomorrow. I went out to do them today and it was kinda windy. I want to get the best I can so I bailed on it today.

Good call--wind gusts mess up coast-downs. Coast-downs don't last long enough to average out the effects of gusts.

Let us know how it goes.