Tilt before every ride?

[MultiRider]

Is it necessary/desireable to do the Tilt calibration before every ride? I did 12 coast downs and an 8 mile out-and-back and created a profile. Isn't the point of all that to ensure Tilt is correct? Wouldn't doing a new Tilt for every ride either be useless or less accurate?

Maybe I'm confused on the mega-coast-down and out-and-back objective.

[fmullin]

Yes and no.
When you finish your ride and download the data into the iBike tool, you can do corrections. One that it does is to offset what appear to be problems with your tilt calibration. So this will then compute new power estimates based upon the corrections.
But the power readings you get during the ride are more likely to be accurate if you do the tild (and wind) calibrations before the ride (or after some minutes to give your equipment the opportunity to adapt to ambient temperature).

[rruff]

Is it necessary/desireable to do the Tilt calibration before every ride? I did 12 coast downs and an 8 mile out-and-back and created a profile. Isn't the point of all that to ensure Tilt is correct? Wouldn't doing a new Tilt for every ride either be useless or less accurate?

I'm wondering about that too. I think the daily tilt cal should just be a quick check to see if it has moved... and if not, you are good.

[iodaniell]

The calibration ride must start with well done tilt and wind offset settings. Once you have a profile, what is in the profile is how much tilt incurred from you being in your calibration riding position on the bike (versus, when you did the tilt NOT sitting on the bike).

Verifying the tilt is good enough, if you have a marked place on the floor/ground where you know what to expect for tilt, but for some folks, tilt can stray on a daily basis due to tire pressure change (do you know what your tire pressures were at calibration?)

[MultiRider]

I did the Tilt and Wind Offset before my mega-coast-downs and out-and-back. I set both tires right at 100psi and the iBike was acclimated to the ambient temperatures. Conditions were good (very little wind, low traffic, no stops or turns) and I had pretty high confidence in the resulting profile based on comparison rides with PT-equipped friends when I did it (December? I fergit, it's been a while).

I did the original Tilt on the hardwood floor of my kitchen. But I did it without being on the bike. Does the out-and-back make the adjustments for the actual Tilt of the bike with me on it?

When I download data, virtually every time I use the Auto Analyze function, it increases my power across the ride by 20-40 watts. That seems like a LOT. I don't know which data to trust -- the original or the post-Auto-Analyze.

Do the 20-40 watt increases by the Auto Analyze software indicate my Profile is off and should be re-done? Do they indicate my body on the bike affects the Tilt in some way that makes the readings too low?

For instance, I did a 100 mile ride 2 weeks ago and the results were, once again, very different pre- and post-Auto Analyze. Pre-Auto Analyze, my average watts were 182 and max of 895. After Auto Analyze, my average watts are 215 and max of 1599. I'm confident the 1599 is wrong since I've never hit more than 1200 watts even when trying and I didn't do a max-power stomping effort at any point during the 100 mile ride. In fact, I'm doubtful of the 895 since I was conserving energy early and tired later. But the actual number isn't terribly relevant since I wasn't going for max watts and it is an infintesimal amount of data in the overall scheme of a 100 mile ride, but it is disturbing that Auto Analyze practically doubled my max watts from 895 to 1599.

I would really like to know the accurate wattage my rides -- 30-45 watts different seems like a lot to me. Not just for the 100 mile ride, but for all my rides. Which is truly accurate -- the raw data or the post-Auto Analyze? If post-Auto Analyze, why would it change my max watts from 895 to 1599? And what do I need to do to get the during-ride readings to be correct?

Thanks!

[iodaniell]

I did the Tilt and Wind Offset before my mega-coast-downs and out-and-back. I set both tires right at 100psi and the iBike was acclimated to the ambient temperatures. Conditions were good (very little wind, low traffic, no stops or turns) and I had pretty high confidence in the resulting profile based on comparison rides with PT-equipped friends when I did it (December? I fergit, it's been a while).

It's difficult to compare your power readings to someone elses unless they are the same weight, ride the same equipment, and have the same aero profile as you.

So, did you do the Tilt and Wind Offset right before the coast-downs and out-and-back or after riding for a while?

I did the original Tilt on the hardwood floor of my kitchen. But I did it without being on the bike. Does the out-and-back make the adjustments for the actual Tilt of the bike with me on it?

Yes.

When I download data, virtually every time I use the Auto Analyze function, it increases my power across the ride by 20-40 watts. That seems like a LOT. I don't know which data to trust -- the original or the post-Auto-Analyze.

The analyzed ride is only as good as the calibration. If you changed any of the attributes of your ride compared to the calibration ride (i.e., position on the bike, more or less aero clothing, more or less aero wheels, more or less aero helmet, ...), then these differences can induce error.

Do the 20-40 watt increases by the Auto Analyze software indicate my Profile is off and should be re-done?

It indicates that there's a difference between the conditions of your calibration ride compared to later rides.

Do they indicate my body on the bike affects the Tilt in some way that makes the readings too low?

Your body weight on the bike will influence the tilt. How much depends on the geometry of the bike and your position on the bike (in the drops, on the hoods, or on the tops).

I would really like to know the accurate wattage my rides -- 30-45 watts different seems like a lot to me. Not just for the 100 mile ride, but for all my rides. Which is truly accurate -- the raw data or the post-Auto Analyze? If post-Auto Analyze, why would it change my max watts from 895 to 1599? And what do I need to do to get the during-ride readings to be correct?

Thanks!

The post processed max wattage of 1599 watts indicates that something is wrong, unless you are a world-class sprinter.

I'd consider re-calibrating.

[racerfern]

Instead of using Auto Analyze switch to the detailed tab. Then click Analyze tilt and power and finally click the advanced button. You will see a green line in the top screen that is probably sloping downward. Check your rides and you might see that they are all or nearly all sloping downward. If you see the green line in various directions or varying angles then you probably need to redo your coastdowns or at least confirm your mount is solid.

If this is the case, it indicates a slight error in the tilt calibration in the iBike profile. Then click on Edit Profile, select your profile and click on "Advanced" (I think that's the button). You will see a screen with various numbers that you can adjust. One of them is tilt. It is usually a negative number about -0.1 to -0.5. This is the amount the bars and the front end of the bike flex downward under your weight. You can try making this number ever so slightly lower, ie: if you're at -0.250 you could try -0.260. You can try even more, but be careful you don't go overboard.

Then go back to one of your previous rides and repeat paragraph one. The green line will get closer to zero. Ideally, you want a zero line pre-analysis. This will give you a very accurate reporting on the ride. In reality there are too many variables to get a perfect zero line but you can certainly improve it.

I think the reason this happens is because during the coastdown procedure you stop pedaling and just lean on the bars whereas on a ride, while pedaling there is less of a leaning effect.

Of course all this assumes that you still go through the pre-ride tilt procedure.

[travispape]

Both Isaias and Fernando gave good answers here. Just to reiterate, if you consistently see the same correction on your rides for the tilt & power analysis (i.e., the green line in the top graph always has a slope in the same direction), then that is an indication that the riding tilt in your profile is off. You can probably improve the accuracy by adjusting the riding tilt in your profile as Fernando described, but the best thing to do would be to repeat your calibration rides the next time you have a good opportunity.

One step the Fernando forgot to mention is that after you adjust the riding tilt in your profile, in order to see its effect in your ride data you need to select the menu item "Tools -> Switch Profile After the Ride..." and apply the profile you just modified.

Travis

[Brodirt]

Perhaps coast down instructions should indicate that the rider should make an effort to put as little weight on the bars/hoods as possible. I will do so from now on.

[iodaniell]

Perhaps coast down instructions should indicate that the rider should make an effort to put as little weight on the bars/hoods as possible. I will do so from now on.

That's not the answer, because you would be hard pressed to replicate that position all of the time. I know I would, especially in a race where I need to focus on several other things.

The answer is what Velocomp is aiming to do--to capture in your profile what your tilt is during rides and adjust for that tilt in realtime and account for it in post-processing.

[rruff]

Perhaps coast down instructions should indicate that the rider should make an effort to put as little weight on the bars/hoods as possible. I will do so from now on.

I could be wrong, but I don't think that will matter. It seems that iBike2 will adjust your tilt based on the 4mile... not the CDs. Then it should be able to sort out your CDs. You *do* want to put about the same weight on the bars as when you normally ride though. I'm not sure, but it looks like it works this way: For most people the iBike will initially register a neg slope when you are on a level road, because you do the tilt cal without sitting on the bike... then when you put weight on the bars the iBike tilts down. So if you do your CDs on a level road, iBike will think you are always going downhill. This will cause it to over estimate your Crr (frictional drag), because slope and Crr are functionally identical (ie a Crr of .005 is identical to climbing a .5% grade). When you do your 4mile, iBike2 analyses it to see if your tilt cal was right, and it calculates the difference and applies this to your CD data. When you upload your CD derived values to the iBike, it will apply the tilt correction whenever you ride. So you just do your unladen tilt cal or check before you ride, and if you apply the same weight distribution as you did in the 4mile, it should be right on.

[alback]

The mount must be completely solid.

Unless there is an internal malfunction, the iBike's tilt is completely dependent upon how well it is fixed to the bike, the stability where the mount is located. On the stem or closest to the stem when using a handlebar installation would seem best. If the mount is 100% and cannot move and your tire pressures are reasonably constant, the tilt should not change from one ride to another.

During the ride the iBikes' tilt changes with rider position, stress or flexing the handlebars/stem and road conditions. It could also be slightly affected by operating the red control buttons. The button position is forward of the mount, therefore pressure on the buttons will flex the iBike downward at each push. This flexing shouldn't move the IBike itself unless the mount can move. It will only affect your values during those moments. Ofcourse your focus is now on the iBike and not on your output during those moments too.

I like the appearance of the iBike, but I have wondered why the iBike module was not designed in the reverse direction. Whereby the screen up front, and the red control buttons directly over the mount itself? This would improve the visibility of the screen as it would be forward of the handlebars. It would also reduce the stress on the mount and the risk of moving the mount when pushing the control buttons.

[travispape]

I could be wrong, but I don't think that will matter. It seems that iBike2 will adjust your tilt based on the 4mile... not the CDs. Then it should be able to sort out your CDs. You *do* want to put about the same weight on the bars as when you normally ride though. I'm not sure, but it looks like it works this way: For most people the iBike will initially register a neg slope when you are on a level road, because you do the tilt cal without sitting on the bike... then when you put weight on the bars the iBike tilts down. So if you do your CDs on a level road, iBike will think you are always going downhill. This will cause it to over estimate your Crr (frictional drag), because slope and Crr are functionally identical (ie a Crr of .005 is identical to climbing a .5% grade). When you do your 4mile, iBike2 analyses it to see if your tilt cal was right, and it calculates the difference and applies this to your CD data. When you upload your CD derived values to the iBike, it will apply the tilt correction whenever you ride. So you just do your unladen tilt cal or check before you ride, and if you apply the same weight distribution as you did in the 4mile, it should be right on.

rruff, I think you have it right, but I just wanted to point out that the right thing to do is use your nominal ride position the same way for both your CDs and your 4 mi ride. If you were to do like Brodirt suggested and try not put put weight on the bars during the coastdown, you would measure a smaller fric factor. This will cause the iBike to under-report power on-the-road. That fric factor accounts for both rolling resistance and riding tilt, so you want to go ahead and use your normal weight distribution in order to get a good measurement of it.

And yes, using the measurement of the riding tilt that comes out of the 4 mi ride, iBike2 will split out both rolling resistance and automatically remove riding tilt from your slope data. This happens without affecting your power measurement as soon as the profile is applied to the ride data. (To be specific, after you download a ride the profile is applied to your ride data either when you click the "auto analyze" button or click the "detailed" tab.)

And to anticipate the next question the above statement might generate: yes, the power is affected by the by a tilt correction if it is necessary. For example, say that the riding tilt that you measured in your 4 mi ride was -0.50% and that on a later day you do an out & back ride where the tilt was off by -0.65%. After the profile is applied and the riding tilt is removed, you are left with a tilt error of -0.15% . When iBike2 corrects that to 0% that it should have been, the 0.15% error does result in a small power change, in this case increasing your average power.

The secrets to happiness are have a solid mount, do a good tilt cal before your calibration rides, and make sure your tilt cal is good before head out on your normal daily rides.