Hi Michael, In my lifetime I have done about 100,000 miles by bicycle, so I have a little experience with that type of transportation ;-) I agree with your statement that the result of lowering tire pressure is " The advantage is better comfort, and durability. " That is exactly why car manufaturers specify a much lower pressure for their tires than the pressure for optimal performance and wear, so you see most car tires getting replaced because the edges of the tire have worn off, while the center of the tire still has half the thread left. Anyway - I doubt that lowering tire pressure can reduce friction, which was our original discussion, but I am happy to learn if you have data to support this claim. Until that time I will keep pumping my tires close to the sidewall max cold pressure, sometimes higher.
Kind regards, 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 10:39 AM To: Electric Vehicle Discussion List Subject: Re: [EVDL] EVLN: Kia Soul EV goes globalandaimsfor120-miledrivingrange Cor, You are just wrong about that, right mind comes in different flavors. You are thinking of racers who can't have low pressure because of puncture. Different situation. On the human powered vehicle side, where recumbents cycles (bi and tri) are used, there is a greater use of tires that are 1.5 to 2 inches in diameter. The loads are greater running into many tens of kg of gear. You can pump fat tires up to 100psi, but the system (bike, rider, tires, gear) turn out to be more efficient between 50 and 75 psi. The advantage is better comfort, and durability. The wider tire allows more deflection befor "snakebiting" pinching the tire between rim and obstacle. This is based on some testing with a rolling drum dynamometer and coast down testing. It is hard to do these test, so there will always be argument about it. You can change this by using very stiff tires which are less efficient. A thin flexible carcass turns out to generate less heat and roll better. When you have a multi kW powerplant all this is quibbling, too small to matter, but the average cyclist can only sustain about 125 watts, on a long tour this adds up and you will care. On Fri, Nov 22, 2013 at 9:27 AM, Cor van de Water <[email protected]> wrote: > 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) > > -- 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... 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