Rolling resistance estimation

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xophe
Posts: 5
Joined: Fri Oct 04, 2019 7:27 am

Rolling resistance estimation

Post by xophe »

Hello,
In Isaac, the estimated Crr for Good asphalt + Clincher + Premium + 7 bar is 0.0043.
I would like to adjust this value more precisely.

Is this value corrected by the Aeropod according to the temperature?
For example, Tom Anhalt uses a correction factor in the following table:
https://docs.google.com/spreadsheets/d/ ... 2047093726

Do you recommend to apply a multiplier to the normalized value found in https://www.bicyclerollingresistance.com/ to use it in the software?

Thank you.
Chris
Velocomp
Velocomp CEO
Posts: 7793
Joined: Fri Jan 11, 2008 8:43 am

Re: Rolling resistance estimation

Post by Velocomp »

The temperature correction is an extremely small factor, and we do not compensate for it in the firmware.

If you wish you can use the normalized value. I would stick with the same value for all your testing, so that you do not introduce unexpected changes.
John Hamann
xophe
Posts: 5
Joined: Fri Oct 04, 2019 7:27 am

Re: Rolling resistance estimation

Post by xophe »

Thank you.

I do not find this criterion negligible but Ok, I myself will adjust the Crr according to the temperature during the test.

For example: GP 5000 - 23 tire + latex tube, 7 bar
- At 10 deg C => Crr = 0.00228
- At 20 deg C => Crr = 0.00264
- At 30 deg C => Crr = 0.00300
Velocomp
Velocomp CEO
Posts: 7793
Joined: Fri Jan 11, 2008 8:43 am

Re: Rolling resistance estimation

Post by Velocomp »

Just for fun I took one of my ride files and used the Crr values provided by you. This can be done in Isaac "Analyze/Tweak CdA, Crr..."

10 C -> 50F -> Crr = .00228 -> opposing rolling watts 16.5W
20C -> 68F -> Crr = .00264 -> opposing rolling watts 18.6W
30C -> 86F -> Crr = .00300 -> opposing rollling watts 21.5W

In this example, going from 10C to 30C (a BIG change in test conditions) causes Crr to increase, and thus causes rolling resistance watts to increase from 16.5W to 21.5W, about 5W.

This 5W watt increase would, in theory, be measured by the DFPM (it requires 5W more power to hold the same speed at 30C, compared to 10C). So, without Crr temperature compensation the AeroPod watts would be "low" by 5W, and CdA would be a bit too high. Adjusting Crr in Isaac would remove the temperature compensation problem.

If you are repeating the same CdA tests with these kinds of temperature differences between test days, then I agree that adjusting Crr in Isaac would be a good thing to do.
John Hamann
xophe
Posts: 5
Joined: Fri Oct 04, 2019 7:27 am

Re: Rolling resistance estimation

Post by xophe »

At the moment, at my place, the temperature is around 5-10 degrees and in a few months it will be 25-30.

5 Watt is not negligible, in my opinion. So, I will update my profile to take into account the temperature.

Thank you for your answer.
EHB
Posts: 129
Joined: Sun Oct 26, 2014 5:52 pm

Re: Rolling resistance estimation

Post by EHB »

As well as temperature rolling resistance also varies with wetness of the road. Ages ago I wondered about this after noticing that it felt very different. From memory the only research I found that was published was using thicker tyres eg. Trailer. A similarly small difference though. No idea how they’d know though. I’m fairly certain the firmware for the Isaac Newton could adjust CRR if there is a big change in surface (eg. Road to cobbles) & this feature was copied across to the Aeropod. I suspect the signals of wet roads would be too hard to see though. If you’re going to manually tweak CRR for temperature I’d also consider tweaking it for wetness too.
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