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  • Tesla: Actually, Consumer Reports Just Reiterated The Bear Case [View article]
    watchingfromabove,
    "you certainly can't experience an acceleration with zero change in velocity "

    You are very wrong. I suggest a good MOOC course in physics. In the mean time I suggest not obscuring this website with jibberish. If you are an engineer you could do community service by enlightening everyone what school taught you.
    Aug 31, 2015. 11:55 AM | 2 Likes Like |Link to Comment
  • Tesla: Actually, Consumer Reports Just Reiterated The Bear Case [View article]
    watchingfromabove,
    "Lying in bed, you aren't accelerating"

    Why do you continue to obscure SA with technical discussions that are WRONG and irrelevant?

    Anywhere on earth (at sea level) you experience 9.8 m/s/s acceleration (including in bed). You can experience an acceleration with zero velocity. (F=mg at sea level, do you see a V in the equation?)
    Aug 28, 2015. 11:00 AM | 2 Likes Like |Link to Comment
  • Here's My Prediction For Tesla's 2015 Deliveries And More On Model X Foibles [View article]
    Paulo,
    Pictures are interesting. There was never doubt in my mind that the falcon wing door was a big part of the production hold up. First, the probability is that the problem of any product program delay can be found in the body shop.

    Second, in May Tesla bought a traditional auto die shop in Michigan. http://on.freep.com/1T... If you need to redesign even one sheet metal part the dies need to be reworked. If you do not own a die shop you may well get a turnaround quote of 10 weeks. The May time frame is when the Model X program announced a delay. Since the articulating door is easily the most difficult body part to make it seems like a good bet that Tesla is anxiously awaiting the reworked dies being delivered from Grand Rapids, Michigan.
    Aug 19, 2015. 03:30 PM | 3 Likes Like |Link to Comment
  • General Motors Is Attractively Valued [View article]
    What is your prediction on how many US government officials and appointees are indicted? After all, the US government was running GM for many years while this was happening and also said nothing.
    Jul 28, 2015. 12:12 PM | Likes Like |Link to Comment
  • General Motors Is Attractively Valued [View article]
    This is a cyclical business and by most measures we have to be getting close to a top in the auto cycle. There is a lot of pain in riding the cycle down. Are you sure the timing is right on this one? There may be good reason for low price.
    Jul 27, 2015. 12:39 PM | 2 Likes Like |Link to Comment
  • Clues About The Tesla Model 3 Battery Size [View article]
    In the next sentence I also say that the important engineering number is Cd xA, not just Cd. Cd by itself tells you nothing about the drag on the car. The Cd X A numbers are generally grouped between 6 sq ft and 7 sq ft with the Model S at 6.2. Again, the Model S has to have a variable Cd because of the variable height suspension. It is likely that marketing posted the best number.

    Here is an article in Car and Driver http://bit.ly/1CZXnEW, hopefully professional writers and actual wind tunnel testing can illustrate. They gave the crown to the Model S but admitted that it was within the testing margin of error of the Prius. Hopefully you agree that the Prius is a volume production car. More to my point, the data table shows that from the best to worst, drag difference is only 4 hp @ 70 mph. In typical mixed driving there will be an average difference of less than 4 hp. That works out to several percent hp advantage on the Model S (less on the D).

    moli and JRP, you take offense as if I had just insulted your first born. If you are objective you have to see that the drag coefficient will not be a competitive advantage. I am not saying Tesla did a bad job on the styling, just that it won't help sell that many more cars if they improve aerodynamics slightly.
    Jul 24, 2015. 07:03 PM | 2 Likes Like |Link to Comment
  • Clues About The Tesla Model 3 Battery Size [View article]
    molli,
    I understand the regen braking and how it CAN be used to 0 mph. I guess that I was making too technical of a point and this is not the appropriate forum for such discussions. Sorry for the miscommunication.
    Jul 23, 2015. 01:26 PM | Likes Like |Link to Comment
  • Clues About The Tesla Model 3 Battery Size [View article]
    Watchingfromabove,
    Good technical articles. I like Straubel's articles but I notice that Tesla is now redacting the graphs. I see where you get your 70% from now, but based on the articles Straubel goes on to say it's complicated. I have seen internal studies at GM (that I no longer have access to) that show the complicated relationship between aerodynamics and the various rolling frictions, etc. Especially using real world driving.

    Relating all this back to investing though, my feeling is that Tesla emphasizes some things like the aerodynamics of the door handles for marketing purposes and it is out of proportion to the engineering importance. Nothing wrong with that. All car manufacturers make claims that are not always accurate in an engineering sense. As an investor though I would not assume that the Model S aerodynamics is a competitive advantage or that they can get more than incremental improvement in order to extend range. Car mags are reporting that the 2016 E-350 will have better aero numbers than the Model S.
    Jul 23, 2015. 01:18 PM | 2 Likes Like |Link to Comment
  • Clues About The Tesla Model 3 Battery Size [View article]
    watchingfromabove,
    "Are you really a mechanical engineer? "
    Nice internet personal attack. Yeah, I was registered in Michigan for 25 years. Worked for GM, including the EV-1 plant and trained at the NUMMI plant. I think I have a handle on cars. Sorry I couldn't get my point across. Really though, do you have a reference for the 70% energy recapture?
    Jul 21, 2015. 06:41 PM | 3 Likes Like |Link to Comment
  • Clues About The Tesla Model 3 Battery Size [View article]
    JRP3,
    "Then why is the Model S cd so much lower than most cars on the road?"

    You are back to my main point, the Model S Cd is NOT that much better than most cars on the road. And quite a number have a lower Cd. More importantly, many cars on the road have a significantly better Cd x A number, which is proportional to the actual drag losses.

    You don't give numbers, so for sake of argument let me give you some:
    Tesla 2012 Model S = Cd X A = 6.2 sq ft
    General Motors 1996 EV1 = 3.95 sq ft
    Toyota 2010 Prius = 5.84 sq ft
    Ford 2000 Escort (Euro) = 6.67 sq ft
    Mercedes 2002 E-350 = 6.24 sq ft

    The Model S drag number is certainly higher now for highway driving since the suspension has been reprogrammed to ride higher. So with all the aero effort on the Model S it barely has less drag than an 15 year old Escort and does not beat efficient cars. A huge number of sedans will fall into the 6 - 7 range so you have to go with a look that the public does not like to get much lower than that.
    Jul 21, 2015. 05:17 PM | 3 Likes Like |Link to Comment
  • Clues About The Tesla Model 3 Battery Size [View article]
    watchingfromabove,

    Most of the numbers you are guestimating are off. A 70% round trip recovery does not add up with real world numbers. Of course there is little braking on the freeway so all that (significant) energy is lost. You cannot use regen all the way down to 0 mph, as a practical matter it won't be used below 10-20 mph. Also, your guess that internal frictions and drag are far less on a Tesla than other cars does not really add up. As I referenced above, there are ICE cars out there with less drag than a Tesla. Also there are many parasitic loads on a Tesla such as battery pack heat pumps. This is energy "overhead" for an EV that cannot be recovered. With the round trip charging losing 10% that would mean you are recovering 78% of the energy to the wheels. Oh, don't forget the variable motor efficiency that might be around 5-10% loss. So that would be a 20% loss just for the electrical round trip (mechanical losses on top of that). As stated above, we know that you won't regen energy on a long highway trip. For me to believe your 70% recapture number it would have to be a range, say from 5% to 70% (worst case to best case). Then the mean regen recapture rate would depend on type of driving, temperature, etc.
    Jul 21, 2015. 04:57 PM | 1 Like Like |Link to Comment
  • Clues About The Tesla Model 3 Battery Size [View article]
    Watchingfromabove,
    "Aerodynamics limits the highway range"
    "Tire inflation plays a major role "
    The total rolling friction of a car (EV or ICE), is quite complex and is generally a trade secret. Clearly you have not studied the role of tires because it is not the aerodynamics that is at issue. And, yes, tires are more important than small changes in Cd.

    "Weight is not terribly important". Wrong. It has significant importance in overall efficiency. Something about F=Ma.
    Jul 19, 2015. 02:47 PM | 2 Likes Like |Link to Comment
  • Clues About The Tesla Model 3 Battery Size [View article]
    JRP3,
    Yes, wind resistance is significant. The changes that Tesla has made with door handles etc, does not change the wind resistance appreciably from many other traditional cars. I have done the calculations and I guess I will have to post them on a blog since everyone else seems intent on believing from their heart and anecdotal evidence from putting a hand out the window.

    The bottom line from a business/ investing standpoint is that Tesla's Cd will not be a competitive advantage.
    Jul 19, 2015. 02:38 PM | 1 Like Like |Link to Comment
  • Clues About The Tesla Model 3 Battery Size [View article]
    @watchingfromabove,
    Your reference to the Wikipedia article was about drag, so I guess you are correct in saying that it was relevant (somewhat). I just get wound up when I see many discussions on this forum (and others) attributing the aerodynamics of a Tesla as a competitive advantage. It is a testament to Elon Musk's marketing prowess that he has convinced so many otherwise thinking people that this is a competitive advantage for Tesla. It is not. If you look at all of the friction forces on a car the aerodynamics do not play that large a role, certainly not a big enough difference to appreciably change the size of the battery. This is especially true for speeds under 60 mph where autos spend most of their time (as opposed to planes, where speeds are always above 60 mph and therefore aerodynamics does become very important). Tesla could increase range more by installing very narrow tires and rear wheel well covers than by getting another .o2 improvement in drag coefficient. Then you would have a goofy looking car like the previously mentioned Honda Fit.
    Jul 13, 2015. 11:28 AM | 3 Likes Like |Link to Comment
  • Clues About The Tesla Model 3 Battery Size [View article]
    @watchingfromabove,
    Your link is to some BS Wikipedia site that really has no relevance to the discussion. BTW, where did you go to engineering school?

    Here is something that every third year engineering student knows: skin friction is highly dependent on velocity. If you follow the link in your own reference you find that drag force is proportional to velocity squared. In laymans terms the drag at 120 mph is four times that at 60 mph. I think a Cessna can take off at 120 mph.
    Jul 11, 2015. 10:14 PM | 1 Like Like |Link to Comment
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