Michael, No bicyclist in their right mind would *lower* tire pressure, except for very rough or sandy roads, since the higher the tire pressure the lower the rolling resistance due to lower deflection. Evey bicyclist pumps their tires as high as he or she can tolerate (or the max that the tire can tolerate) for minimal friction. Only for loose sand or rough roads does it have advantage to have low tire pressure and increase the contact patch surface.
Cor van de Water Chief Scientist Proxim Wireless Corporation http://www.proxim.com Email: [email protected] Private: http://www.cvandewater.info Skype: cor_van_de_water Tel: +1 408 383 7626 -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Michael Ross Sent: Friday, November 22, 2013 4:51 AM To: Electric Vehicle Discussion List Subject: Re: [EVDL] EVLN: Kia Soul EV goes global andaimsfor120-miledrivingrange The levelness is the point of interest for me. Two identical EVs, one goes around a flat circuit or out and back, it does not matter. The other goes on a hilly route of equal length. I will give the the extra inches from climbing, but give me that the inclines are not very great, and you can simply maintain a constant speed on the inclines by simply backing off or adding power. Constant speed washes out the effects of increased air drag. There is no difference of any significance, to the power needed on either route. You get every bit of kinetic energy back on the downhill runs that you converted to gravitational potential energy on the uphill runs. You end at the same point with the same potential energy as you started. When you start tallying up the heat losses, the greatest by far is the heat generated pushing through the air. Rolling resistance is very small in comparison. On bicycles the heat generated jiggling things around, sliding straps, and chafing fabrics, are on the same order. You can actually save a little by lowering tire pressure, but not too much. I will grant for making a comparison between vehicle ranges and performance that a flat route is appealing, but it won't change the results that much unless the down hill speeds are significantly different. DIfferences in ambient wind, driving style, and so on, are harder to control and add up to significant noise in a study like this. You can only get results that are dependable by a valid, statistically significant set of runs, because the noise is too great. I have done drive cycle testing on cars, and read a fair amount about air drag testing on streamlined bicycles. Human powered vehicles are particularly concerned with the minutia of energy loss in vehicles, as the power source is limited to only 250W or so. The main thing to carry away is minimized air drag, by design or drive style. You may not even notice the losses due to vibration of too high tire pressure on an EV as the use of energy is profligate in comparison. Variations in the efficiency of motors at different speeds and loads is probably noticeable, I would anticipate a sweet spot for each particular EV. VFDs are probably a nice way to minimize this and improve efficiency. They do a good job on HVAC systems, FWIW. On Fri, Nov 22, 2013 at 3:16 AM, Martin WINLOW <[email protected]> wrote: > What about the energy losses of (effectively) constantly having to change > direction on a circuitous course (or any course - especially a twisty > mountainous one - lots of hair-pin bends)? This would manifest itself as > the tyres scrubbing on the road surface giving off heat, noise and wear on > the rubber/road. Not big but still significant. The losses on the outward > trip would be aded to those of the return. They would not cancel out like > a change in elevation would... or am I missing something? MW > > > On 21 Nov 2013, at 01:09, Cor van de Water wrote: > > > Hi Michael, > > Since this is a theoretical experiment, we might just as well focus on > > that theory and indeed, at first blush is appears that the theory says > > that if you have a closes course, your *potential* energy level is > > identical at finish as when starting, so there is no net build-up or > > release of energy other than the friction and kinetic energy, since any > > height gain or loss must be made up by the end of the trip. > > > > However, an electric motor works different than an ICE. Where the ICE > > motor has a weird efficiency change (weirder for petrol as for Diesel > > engines and the Prius' Atkinson cycle is again slightly different than a > > regular petrol ICE) the efficiency of the electric drivetrain is in > > theory perfectly linear falling with the amount of power delivered, > > since losses go up squared with the current (force) delivered. > > > > Result is that if half the drive causes you to use double the current > > and half the drive you can maintain the speed downhill at zero current, > > your total *loss* will have doubled. It is 4x as large during half the > > drive, compared to the 100% level ride. > > > > So, in theory, diving over hills and mountains at the same speed should > > consume more power than driving the same speed and distance on a level > > road. > > > > In an electric drivetrain, loss may be at or above 30% at full throttle, > > while at half throttle it is typically at or below 10% for the same > > reason. > > So, the total energy difference is not very big, you may go from the > > energy consumed at level road to an increase of around 8% for the > > example drive half uphill and half downhill. (level would be 92% energy > > to the wheels, 8% loss, for the doubled loss in the hills you would have > > 16% total loss so the energy consumption rises by 8%) > > > > Hope this clarifies, > > > > Cor van de Water > > Chief Scientist > > Proxim Wireless Corporation http://www.proxim.com > > Email: [email protected] Private: http://www.cvandewater.info > > Skype: cor_van_de_water Tel: +1 408 383 7626 > > > > > > -----Original Message----- > > From: [email protected] [mailto:[email protected]] On > > Behalf Of Michael Ross > > Sent: Wednesday, November 20, 2013 4:36 PM > > To: Electric Vehicle Discussion List > > Subject: Re: [EVDL] EVLN: Kia Soul EV goes global and > > aimsfor120-miledrivingrange > > > > Cor, this is really a theoretical topic. Why should a level ride be > > easier > > than a hilly ride if it is a circuit? > > > > I disagree about regen saving anything except when used for braking, > > then > > you are trading waste heat for some charging.. If you use regen to slow > > down on hills you are causing an inefficiency. > > > > If you are on a hill that is too steep for safe coasting and brakes must > > be > > used, then regen is better than heating your brake rotors. > > > > If you take all this out of the thought experiment, then hilly and level > > are equal. > > > > > > On Wed, Nov 20, 2013 at 7:22 PM, Cor van de Water <[email protected]> > > wrote: > > > >> Michael, > >> How often do you encounter a steep road that is completely straight in > >> the mountains? All the roads in the surrounding mountains that I know > >> have sharp turns, for which you will *definitely* want to slow down. > > So > >> except if you are in roller-coaster country, having regen will save at > >> least part of the energy from the downhill run when you need to slow > >> down for the next turn... > >> > >> BTW, it may be that the information is skewed due to the redefinition > > of > >> electric vehicle by some manufacturers. I have noticed that my Prius > > can > >> get better mileage going over a large hill than when doing a steady > >> speed in flat terrain. This is probably similar to the "Pulse and > > glide" > >> hypermiling technique. This has of course nothing to do with pure > >> electrics, but since GM calls their plug-in hybrid an EV, that may be > >> where the confusion comes from... > >> > >> Regards, > >> > >> Cor van de Water > > _______________________________________________ > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub > http://lists.evdl.org/listinfo.cgi/ev-evdl.org > For EV drag racing discussion, please use NEDRA ( > http://groups.yahoo.com/group/NEDRA) > > -- Put this question to yourself: should I use everyone else to attain happiness, or should I help others gain happiness? *Dalai Lama * Tell me what it is you plan to do WIth your one wild and precious life? Mary Oliver, "The summer day." To invent, you need a good imagination and a pile of junk. Thomas A. Edison<http://www.brainyquote.com/quotes/quotes/t/thomasaed125362.html> A public-opinion poll is no substitute for thought. *Warren Buffet* Michael E. Ross (919) 550-2430 Land (919) 576-0824 <https://www.google.com/voice/b/0?pli=1#phones> Google Phone (919) 631-1451 Cell (919) 513-0418 Desk [email protected] <[email protected]> -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20131122/a4bc 9a90/attachment.htm> _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA) _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
