Newton on a Brompton folding bike

Newton on a Brompton folding bike

Postby theller » Tue Jan 05, 2016 12:19 pm

Hi,

I've attached my Newton (in addition to other bikes) to my brompron folding bike. I did an initial setup which generated the values Crr = 0.0087 and CdA = 0.39.

After some days, I did (again) a cal ride followed by 6 coats downs. This generated totally diffent values: Crr = 0.0183 and CdA = 0.695.
Do these values sound sensible? They create approx. double the power values than before... Hoever, the initial default values are probably more suitable for a racing bike.

Thanks
theller
 
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Re: Newton on a Brompton folding bike

Postby Velocomp » Tue Jan 05, 2016 4:54 pm

Actually, because you are sitting straight up on your bike, these values may be quite reasonable!

Please post a ride file...
John Hamann
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Re: Newton on a Brompton folding bike

Postby theller » Wed Jan 06, 2016 4:16 am

Ok, that's what I wanted to hear.
Here is a sample ride file with this profile.
Attachments
iBike_01_05_2016_1857_18_km.ibr
Brompton ride file
(160.45 KiB) Downloaded 64 times
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Re: Newton on a Brompton folding bike

Postby hamishbarker » Wed Oct 05, 2016 5:26 am

the 16 inch bromton wheels with the standard brompton green schwalbes will be quite high Crr. On my 26 inch mountain bike with schwalbe marathon plus tour (rather chunky) at around 2 bar (low pressure for smooth but inefficient rolling), I consistently get crr around 0.01 and CdA around 0.4-0.45 both with coast downs and also correlating with a powertap file.

The brompton 16 inchers will be slower still, and as john says, 0.018 might not be wrong, and the very upright position could well give your quoted CdA circa 0.6.

But I would also recommend that you find a section of flat off-street (but smooth-ish) cycle path to do a good set of coast downs, at least 10 runs. before you do the coast downs, first ride for 8 minutes to ensure that the tilt calibration is settled down to the right value, then do a wind sensor calibration, and a trip reset and make at least a 10 minute out and back in calm conditions. then do the coast-downs and post process with the setup menu item " Device > Setup > Download coast downs and calibration ride". The procedure isn't perfectly documented in the newton manual. I made the mistake of trying to do a cal ride, but then the isaac software thinks you are setting up a new bike. No need to set it to cal ride before coast downs, but you do need to do the 8 minute tilt cal pre-ride, then wind sensor calibration via the setup menu, then an 8 (or more) minute out and back ride to ensure correct wind sensor calibration in the coast down processing.

I find this works well but even with 10 coast downs, two different out and back rides (pre and post the coast downs) gives different crr/cda results. It's a very sensitive calculation. the best way is if you can manage to borrow someone's powertap P1 pedals in order to corellate the DFPM file and the calibration out and back ride file. Even that can be sensitive.

Do persevere though, I am happy now that I have good profiles set up now for three mountain bikes and a commuter bike, all giving good power data, checked with a powertap wheel. However front or rear suspension can mess things up - and will on the brompton too since the movement of the rear suspension triangle means that the angle of the newton/powerpod is not fixed with respect to the hubs (which the PP/newton algorithms depend on to accurately calculate power numbers.
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