When to recalibrate (tyres / weight)

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Garf
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Joined: Fri Jun 19, 2020 4:32 pm

When to recalibrate (tyres / weight)

Post by Garf »

My understanding is that the O&B ride mostly configures the Wind Speed Factor, and everything else is automatically calibrated/adjusted the first 90 seconds of each ride.

During the configuration I had to set a tire inflation (which I'm guessing is used to guess Crr?). Is this something that is also automatically updated during the start of a ride, i.e. when I change the inflation pressure or even the tire type? Same for aero position or clothes (CdA)?

If I compare similar rides (in similar winds) in Isaac, would I expect to be able to see that rolling resistance Watts drops with better tires? Same for aero losses with better fitting clothing?

What about weight? Only matters if there's significant changes - that I understand. But can I change that from the Android app, or would that overwrite the WSF calibration?
Kcblair
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Re: When to recalibrate (tyres / weight)

Post by Kcblair »

Bump. I'd like to know also. Good question.
Velocomp
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Re: When to recalibrate (tyres / weight)

Post by Velocomp »

O&B ride sets Wind Scaling Factor and tilt calibration. These are factors that are used in all subsequent rides.

Default Crr is set during initial calibration and is based, in part, on tire pressure.

On the road It is adjusted by measured on-the-ride road roughness. However, unless you manually reset tire pressure with the Setup Wizard you won't change the default value of Crr.

Same principle is true for CdA.

AeroPod can definitely be used to measure the Crr effect of different tire pressures, and CdA effect of better clothing.

You can change weight using the app, but this will likely change the CdA value that was established by Isaac. If you're going to use the app, then use it from the initial setup, and continue to use the app whenever you change something in your profile.
John Hamann
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lorduintah
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Re: When to recalibrate (tyres / weight)

Post by lorduintah »

Based on what John is saying - I think to get the most information from changes in tires, tire pressure, maybe clothing and any other variables you might think about - without getting a AP version and DFPM (which allows a few more degrees of freedom to experiment over) - then using the same section of trail or road and running calibrations with these system variables (here I mean system to be: you, clothes, bike, tires, pressure and whatever else is part of the cycling experience) might allow you to evaluate - post calibration how your ride ends up requiring change in power. This, of course, is a lot more to keep track of than just using an AP as John mentioned. But here the key to getting information is to minimize all variables that you do not want to change to see what impact those you are intentionally changing do alter.

Also, another way to go after some of this - use the same calibration from a base configuration. Make all your changes systematically and with each one go for a ride (not a ridiculous long ride, but say maybe 10 miles (5 out, 5 back) - over the same route. The best way to do this is with a statistical approach - if you are up to it. Using something called Design of Experiments, DOE, you can run a series of rides with variations in the configuration.

Using the original calibration profile - after the ride you can apply what ever change to calibration ISAAC finds and compare the revised (post analysis) output to the baseline 10 mile ride before you made any of the configuration changes. Along the way you would also insert - randomly - more baseline rides - this allows a better understanding of the reproducibility involved and thus the confidence that any of the changes in configuration led to any desired improvements or better operating conditions.

As an engineer, I have used the DOE to understand what knobs (and corresponding settings of those knobs) on a piece of equipment influence a process - making it more or less efficient, increasing or decreasing yields, or having an impact on reliability, for example.

This again is involved and time consuming - whereas using the AP some of the complexity is resolved.
Garf
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Re: When to recalibrate (tyres / weight)

Post by Garf »

Yes, I think you understood what I am trying to do: to get some indication of improvements without an AeroPod (or specifically, getting a DFPM anyway). My thought that this could work as based on seeing Isaac split up the power data into aero and rolling resistance. Of course it would need fairly repeatable rides.

After playing more with Isaac, and together with John's answers, I think I understand now that what I want isn't possible - at least not without making the rides repeatable to an unrealistic extent.

Specifically, the "AERO" and "ROLLING" wattages are calculated from the Crr and CdA, and those values are not calibrated/computed, but derived from the device setup. (John clarified Crr is adjusted on-the-fly if you hit, for example, a cobblestone section, but starting from the base value of the setup)

In Isaac this is most obvious if one uses the "Check Calibration" function, as that shows the used Crr and CdA values are exactly the ones you enter via the setup. It also easily allows checking the impact of changing the values.

By playing with this, one can clearly see that tire inflation pressure has a quite negligible effect, as has rider weight unless you gain or lose a lot of kilos. Even hoods vs drops - for the entire ride! - is like ~5W at my speeds. So there's no need to re-calibrate nor update the profile in 99% of the cases.

But upgrading to something like a set of Grand Prix 5000's is another matter: this can easily mean 10W difference as Crr will go from ~0.006 (Utility) to ~0.0045 (Premium). The tested Crr of these tires is even lower, close to 0.0032, for 15W difference.

I haven't tested whether updating this via the App overwrites the WSF calibration (my understanding is that Tilt is easily auto-corrected by the PowerPod itself so its calibration doesn't matter anyway!). But realistically, changing tyres (not inflating them) or shedding/gaining massive amounts of weights are the only cases in which it would be worthwhile to fiddle with the profile, and re-calibrating would only ever be needed if you change the position where the PowerPod is mounted on the bike.
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