With web programming, a lot of the initial hassle and set up is gone, and visual learning/iteration by hitting refresh is very easy. So I would say, almost as young as they can play around with a web browser, and type on a computer. You can immediately start seeing results by typing in the Chrome inspector console. I think even a 4-year-old would be able to understand an if/else, but I'm not behavioral psychologist.
yeah that's a good point; I really wonder about conditional statements though, I think control flow should be straight forward, but I would think you might need to start off with variables and primitives at least.. what do you think?
The thing is we have a lot a lot of leverage on the technological side. Choosing a behavioral and societal change vs. technological is always a trade off - but for this case some things make improving the technology much easier. The median age of a car in the US is about 11 years vs. 36 years for homes. Cars are individually replaced whereas reconfiguring homes that are on fixed land is a much more difficult task. If you're asking about an individual level I agree it's a choice, and you've covered those pain points say within a metro area. However if your family is in many South/West cities - say the Houston metro area or Las Vegas, distances are going to be pretty far. Amazingly, Los Angeles actually has pretty low average miles per year - one of the lowest for metro areas.
While the technological advancement is pretty much a universal win, the behavioral change isn't, or is at least debatable/not everyone's cup of tea - a lot of Americans prefer to live in large houses with lower density neighborhoods (of course others prefer large dense cities). Many also live in rural or semi-rural areas, and the US has a lot of cheap land compared to say Western Europe. Zoning in a city is dictated by those residents. However with better technology and cheaper energy, the expense of this lifestyle will be lowered and allow more choices (similar to how remote work allows people to remove geographical limitations). If we think about developing countries, any efficiency gains will also reduce their energy impact as consumption increases
Right now local transit in the US is often less energy efficient per passenger-mile than a solo-driven Prius or Insight, or even the average-loaded (gasoline) passenger car. The numbers vary of course based on passenger load and route efficiency of course.
It's not always the most efficient for every car, but there are lots of charts showing this tradeoff. Some cars are more efficient at 65 or 70 than 55 (97 Celica), but in modern gas cars, 40-50mph is where you hit a peak, and you start getting worse from there. 40mph on the highway is painfully slow though, so people generally pick an optimal point higher than that.
(One inconsistency I've found is how the Motor Trend test below sees a very high peak at about 40MPH and a decline after, while other sources show a flatter peak). And 55MPH seems more like a magic number the author picked, but not a bad one if we don't know the model.
Generally cars are geared so the engine begins entering its optimal / most efficient RPM range where it can produce more torque in top gear around 40-50mph, and rolling resistance and wind drag (which is a cube function of speed) contribute to make mileage worse after that. Usually the speed at which you first shift into top gear and cruise comfortably is close to optimal. Efficiency doesn't start dropping for a while because of the cubic nature of drag, and the engine sometimes is more efficient at higher RPMs for a bit (see nols' post on manufacturer optimization).
Fun fact: At top speed (254mph), a Bugatti Veyron will use its 26 gallon tank in 12 minutes.
As I stated in a sibling, this still boils down to "this is how current cars are built." I would imagine if you looked at the average vehicle built in, say, the 1940s, you would see a vastly different "optimal" number.
Which is all to say, do we expect this to stagnate forever at 55? Is this a hard physical limit? I understand drag gets higher there. Are there no tricks left to us?
And again, I fully concede that this is likely not the most pressing fact around. Just one I am curious on.
OK, now I understand where you're coming from. The physical limit is that at higher speed, we must expend more energy per unit of distance, to overcome drag (relatively little is lost in braking or rolling resistance of tires.) [1] So on any planet with an atmosphere you will have to contend with this.
The 'ideal' speed isn't really even 55MPH, but lower if you had all variables at play to get the maximum MPG at any speed (probably 30-40MPH), but manufacturers expect people to cruise on the highway faster so they adjust the gearing. If you're asking how to push out the curve so that going faster than 75MPH doesn't offer a huge loss of speed, lower drag coefficients are the trick. Or switching out of the 4-wheels-on-ground automobile.
In this generic diagram, the ratio of drag (air)/rolling (ground) resistance is 11-to-7. As you get to higher speeds, the ratio tips even more in favor of drag.
Fun fact: The Bugatti Veyron gets 2.15MPG at its top speed of 250MPH.
This was exactly the angle I was looking for. I am still not entirely satisfied with this, as it does not flat out state why better gearing couldn't achieve some increase.
That is, my naive understanding is aligned with what a sibling post said. That there is an "ideal" torque rating of my engine. Seems that if my cruising speed isn't stuck at that number, than some gearing changes could be made to put me there. Why does that not work? (Adding a 7th gear, for example, seems to be a natural idea.)
I'm curious to hear that the ideal speed would actually be below 55. Do you have good references on that?
Also, I'd assume the "switching out of the 4-wheels-on-ground" refers to such as trains and friends?
For an automobile, at cruising speed, the force of the drivetrain pushing the car forward, and the forces of drag and friction are balanced (If the net force is zero, the acceleration is zero).
In the engine and drivetrain, force per unit of fuel is dependent on velocity (this is probably a pretty complex dependency), but you can probably tune the system to have peak efficiency at whatever speed you want.
For aerodynamic drag, it's a function of the square of velocity. You can certainly work to lower the drag coefficients, but whatever the force is at 39 mph, at 55 mph it will be about double, and about 78 mph will be double that.
Realistically, it makes sense to put the peak of engine and drivetrain efficiency in the range people are going to be driving the most; so this is why many vehicles will be most efficient around the 55-70 range.
If you're willing to radically change behavior, you would likely have a much more efficient vehicle if you tuned for 40 mph, and people drove it at 40 mph. At lower speeds, other frictional forces become more significant as well, so maybe tuning for 5 mph isn't a great idea.
> That is, my naive understanding is aligned with what a sibling post said. That there is an "ideal" torque rating of my engine. Seems that if my cruising speed isn't stuck at that number, than some gearing changes could be made to put me there. Why does that not work? (Adding a 7th gear, for example, seems to be a natural idea.)
You could add more gears -- or you could just use a CVT.
Longer gearing will improve the high-end efficiency where it wasn't yet optimal - to help 90MPH you could target that with your super 7th gear at "ideal" torque/RPM. However the overwhelming aerodynamic drag means the peak efficiency won't shift to the right much, and it'll probably stay around 40-45mph (the power required is proportional to the cube of speed and 11x stronger at 90MPH than 40MPH) [4]. In many cases that super 7th gear wouldn't help 40mph (peak) at all if 5th/6th had already optimized 40mph.
I think the 55-70 range is pretty optimized on production cars today, including those with 5 or 6 speed transmissions - but you may be able to make more gains with longer gears/a CVT at speeds above that. In an earlier age of 3-4 speed autos (and sometimes a national 55mph limit), manufacturers had fewer gears to work with so a super long gear for 80MPH efficiency would trade off midrange efficiency and acceleration, and the EPA didn't test that anyway until 2006 w/ higher highway speeds
[4] My reference on the ~40MPH ideal speed (which I'm now more convinced about is the ideal for cars today) is the Motor Trend [1] test (all economy sedans peaked 35-40ish), several Hypermiler/car specific forums [2] and some personal cruise control tests with some rental/Zipcars with a digital gauge. Other ways to test include Scangauge/the Torque Android app. (The reason the ~40mph peak isn't even lower, is due to gas engines especially larger ones, being less efficient if they produce too little power - there is a minimum RPM at idle and always friction). So my earlier statement of "optimal peak would have been 30-40" - it's already around 40, and it doesn't have to achieved in top gear.
I put "ideal" in quotes earlier since the torque peak is one of many factors for the engine - the ideal cruise RPM is almost always lower due to less engine friction and lower pumping losses when you aren't asking for full power. If you ask for more power, your optimal RPM goes up closer to the torque peak. A generic motor from a friend's auto engineering class [3] (If you say had a Honda S2000 with a torque peak at 7500rpm, cruising there would kill your mileage)
Yeah, though by 4-wheels-on-ground I was mostly referring to flying/maglev type vehicles, or perhaps a vastly different design that had very little aerodynamic drag
Thanks for the comments and further reading. I see I should have also made clear I was never expecting anything in the upwards of 90mph range. The article was quite leveled at 55, though. Seems upping that to 60/65 should at least be possible.
I'm not sure I understand what you mean on "if 5th/6th had already optimized 40mph." Again, it may be my naive view, but I had thought each gear would have its own optimum. Or, were you just saying "top, be it 5th or 6th"?
I can definitely understand the wind resistance point. It really just comes down to my being somewhat incredulous that it is pinned at a mph point. Surely with better gearing, we have pulled the number up from where it was back when I had a 3 speed automatic? You seem to be implying otherwise.
Got it - I think you're asking why the peak is still so low at 40mph, and why we haven't shifted it toward 55, or 65. The reason there is a peak at all and we aren't most efficient at 5mph is due to (1) for gasoline cars, low efficiency at low loads - a motor may have a maximum of 200hp but only asking 10hp to power you means you'll pay a lot of frictional/throttling losses (at 10hp you'll be in the far bottom left in diagram [4]) (2) "fixed costs" per unit time - power steering, power brakes, alternator for electronics. Those two factors push us out to the right, whereas wind and rolling resistance push us to the left.
I'm not an automotive engineer so I don't understand the overall system equations, but I suspect for a given vehicle weight of ~3000lb, drag coefficient ~0.30, and 4-cylinder gasoline motor characteristic that provided sufficient passing acceleration, the "solved equation" for economy cars happens to end up in in the 35-45 optimal range. Gearing can't move the peak so much as make the decline less severe. (In my experience 4 speed autos generally had similar top gear ratios to 5 speed manuals of the time, but had other losses/at in-between speeds)
If you wanted to just shift the peak to the right, you could (1) equip an engine that is very large/extremely inefficient at low power outputs, and had higher parasitic losses and (2) reduce drag. Thus, it would make sense to drive faster, to move your motor out of the extreme bottom right in [4], and "spread out" those parasitic losses over a larger distance.
Adding more gears makes the slope go down less steeply after 40mph (but it's always going down consistently - see the Motor Trend article). The reason I used a 90mph example is I believe most 6 speed transmissions today already have 6th gear optimized for ~70mph cruising due to their motivation in post-2006 EPA testing. By optimized, that doesn't mean the optimal MPG in that gear occurs at 70mph, just that we've eliminated the gearing mismatches/inefficiencies compared to a CVT, which always has "perfect gear ratio". You could still add a 7th and find improvements at 80/90 probably.
So if 5th gear (in a 6-speed) had optimized 40mph, and 40mph is inherently more efficient, we would be driving there instead for overall peak MPG. I was trying to say that with enough gears, you don't need to be in top gear for optimal MPG due to drag. Hope that makes sense
I was actually asking why don't we keep the peak at 55 from dropping till later. I fully grant this is because I was ignorant of the lower peak at 40.
I should probably have added that most of my understanding in gearing comes from bicycles. I fully expect that my limited understanding there will not necessarily transfer. However, it has built up an intuition that gearing makes a huge difference. It is easy to get a sense that the other components of the equation have the final say, but it is impressive the difference going from a mountain to a road bike.
And again, thank you for the responses. I don't know as that I learned anything I can use in making decisions, but I do feel I have at least learned something.
Got it, hope that helped! I'd be very interested to see what the analysis is for a bike and what the optimal human efficiency is like.
In my experience riding road/hybrid bikes vs. mountain bikes, the lower resistance tires reduce the effort even if the gearing is similar. I'm also guessing the human leg has a narrower efficiency range in terms of RPM and power produced, so bikes usually have 15+ gears.
Now that I think about it, the 'simplest' way to explain the curve is - the vehicle/powertrain variables determine the efficiency curve with ideal gearing e.g. a CVT. If you have a 4 speed transmission, you choose 4 optimal points and imagine a steeper efficiency fall off in between each point (4 flattened parabolas with vertices at the optimal points).
The wikipedia article covers it decently.[1] And, the tires definitely have the most obvious effect at getting up to speed. However, I know that my top speed is higher on my road bike than it is on my mountain bike of similar tire size. I have mostly attributed that to the gearing. (Simply put, I am peddling as fast as I can on the mountain bike and going slower than a modest peddle on the road bike.)
Nit: aerodynamic drag force is modeled as quadratic (squared) with speed. The power required is force times velocity, which means the power is cubic with speed, but the force is only quadratic.
When taking into account wind resistance, the optimal speed for efficiency varies greatly with the current weather conditions too: with a tailwind, the optimal speed goes up, while the opposite is true with a headwind.
Usually the speed at which you first shift into top gear and cruise comfortably is close to optimal
Although automatic transmissions and lack of tachometers are probably responsible for this, I've noticed that a lot of drivers remaining at the upper RPM range for a certain gear while cruising, when they could've sped up 2-3MPH and upshifted. I don't know if there's a term for this, but it's certainly recognisable as a passenger: the engine is much louder than it should be, often with accompanied higher levels of vibration and discomfort.
Over the long term you expect the weather to average out and cancel itself out of the calculation. The question is does the headwind lower your efficiency more than the equivalent tailwind raise your efficiency?
Yes, in general getting 50/50 up+down hills, as tail+head winds decrease your total efficiency, as if you drive both directions (getting both the advantage and disadvantage), then you tend to drive the disadvantaged half slower (but not using less power, so no efficiency benefits from that) = it affects you longer = it has more effect on efficiency.
In a way, it also helps turnover of tables - it's a soft way of ensuring new customers can get seats and the people who got there first don't stay all day (short of an explicit X hour limit)
Great points, especially on the loans. I'd like to add that you don't need REG 262 except in special circumstances, such as if the seller doesn't have the current title, or with loans (maybe that was part of the context though) [1]. But avoiding that trip to the DMV is a great blessing
When I sold my vehicle in CA, both the buyer and I filled out the transfer of liability online [2] - no appointments needed. The title ("pink slip") contains the bill of sale with the odometer reading that you would otherwise put on REG 262. The buyer and seller both sign the title which also has the paper version of the transfer of liability should you be inclined to mail it. The buyer generally will have to go to the DMV to pay use tax and turn in the old title.
In California it's even easier than getting a notary - you just need signatures on the title ("pink slip"), and then both parties can fill an online form for transfer or liability. The buyer then goes and hands over the title to the DMV at some point in the next (10) days, getting a new title in the mail.
For as well me I've had a decent experience on Craigslist - just some due diligence and research on best practices and you're good to go. But it does take some time and patience and dealing with flaky buyers. Just ignore the lowballers and the non-serious. However I'm sure a lot of people would love this type of service, especially in common scenarios where the actual seller is busy so they try to proxy it to a family member who really isn't interested in selling it. Or when they've moved out of state and buyers don't want to deal with that
Great service! A lot of people don't have experience or simply don't want to deal with the Craigslist experience. Putting another option between a private party sale and the dealer is great.
Questions that immediately come to mind - how do you handle negotiations, and how do buyers pay? How do you pay the seller afterward? (cash, verifying a cashier's check - other comments point out the common scams etc.) (Or is Instamotor just a transaction facilitator)? Where is the vehicle listed? Do you handle smog checks as well (for California)? <- Those are the most common things I go through the used vehicle process.
Also, how do you filter out non-serious buyers, especially for performance vehicles? A lot of sellers ask for some sort of proof of payment or cash ready before a test drive. It seems like you're mainly handling high-end cars where the 5% commission will pay off too, how does the model change for say a $5K vehicle?
Finally as a buy I would want to do my own inspection unless the inspection is at a mechanic I already trust - there is way too much conflict of interest having the selling side do an inspection.
Some ways to get it more buyer-friendly would be to offer a CARFAX as well.
> Also, how do you filter out non-serious buyers, especially for performance vehicles
I cannot emphasize the importance of this. I have a 2005 Lotus Elise that I would love to part with, but I'm really, really nervous about an inexperienced driver blowing the clutch or just coming over for a joyride.
I have had a lot of sports cars and test driven a good number as well. A lot of owners are like you and some wouldn't even let me drive the car, I had to sit in the passengers seat while they did everything. I could ask to do certain things like if they would brake check or accelerate, but that was the limit.
What I would propose is letting people ride with a trust local mechanic with the mechanic driving. That way they can make sure a professional is driving the car, can pick up on any issues, and can be honest with the potential buyer.
All of these are excellent questions. I'll tackle them 1 by 1 (the is to say, we're still working through some of these items, this is just our current methods).
1. How do we handle negotiations: We talk to you, the seller and work to find a fair market price for the car. We have dealership level tools available for this. We come to an agreement on the minimum price you'd take. From there, we negotiate with the potential buyer and can take an offer up to the minimum we agreed upon. Anything lower we'd need explicit permission from you.
2. The Buyer makes a cashiers check out directly to the the seller. We deliver it to them.
3. The vehicles are listed everywhere we can, including some of the traditional places like Cars.com and autotrader. For certain cars, we also do very specialized listings (e.g. for Porsches we list or Porsche enthusiast forums, etc...).
4. We handle it all, including smog checks.
5. We get paid at the time of the transaction usually directly with proceeds from the sale.
6. With performance vehicles we are very very diligent about this, currently doing it manually. We represent a few very high value Porsches. We research all of the buyers (again manually, but we'll work on that) to see if they're legitimate and also work to get commitments from them. If we see an 18YO kid that wants to test drive a Porsche, we won't necessarily disallow it, but we'll make sure that he has the financial resources and intent to purchase the vehicle. It's not perfect, we're still working on this, but I can tell you all of our owners have been very very happy with the people test driving so far.
--Edit--
We currently offer CarFax. One thing we have to improve is enumerating the depth of service that we provide.
Be careful, forged cashiers checks are a common scam.
As seller to protect yourself you need to e.g. meet the buyer at his bank and get cash or a certified check that the bank prepares at that time. Or use some kind of insured escrow service.
Thanks AMS6110,
We actually verify all cashiers checks immediately when received. It's usually pretty easy to google the bank the check is from and call them to verify the authenticity of the check.
Are there any better financial tools out there for this? Cashier's checks are almost free, but prone to fraud, wire transfers are bullet proof, but expensive.
On point 1, have you considered innovating in the commission structure as well? If we've agreed on a fair market price, then I'd rather structure the commission along the lines of, for example, 25% of (sale price - 80% of fair market price). If you then sell the car for the fair market price, then you'd receive the same 5% commission, but you'd have much more incentive to drive a hard bargain.
1. 90% of questions asked about a car are standard (e.g. what's the history, what's the mechanical, is it a clean carfax). We can pre-empt this by having the answer ready.
2. For answers we don't have, it's the standard "let me get back to you" and ask the seller.
This is great service! I think you can simplify the process further for buyers. Maybe you can schedule group of car viewings on weekend, say in parking lots of local mechanics (autozone, etc etc) . This way buyers won't have to schedule multiple views and sellers will have to part their cars only on weekends (similar to house viewings). Buyers then, if they choose too, can get the cars evaluated by local car mechanics.
What I really want to know is, if the conspiracy about Yelp taking down reviews based on whether you pay for its premium services. I imagine this is most of the fight with FTC complaints. I've seen so many accusations, but no actual proof of a page losing its reviews, or even a recorded phone call with a rep (legal in most states, one of the exceptions being CA), just stories. I believe most negative reviews are legit and many businesses that complain about getting them are in denial.
Aside about reviews: Everyone loves to hate on how Yelp is biased and reviewed by idiots, but for me it's been better than the alternatives, and the star ratings generally reflect quality (especially for places with 100+ reviews). I usually don't have the same tastes as professional critics, since they often have a far higher price range and pay attention to the professionality of a restaurant, and have their own biases away from the "plebeian" tastes. The sample size of a lot of Yelpers is usually pretty effective in finding good food. ZAGAT et al often also don't review small tea shops, food trucks, etc.
I have one data point against yelp: I created a website for a small business and they asked me about yelp's services after getting a call since they were not technologically inclined (nice elder couple).
I told them it was not necessary for the success of their website, that the decision was up to them and they should not feel rushed into signing up for extra advertising since the site was just launched. I suggested they wait it out and see how much traffic they received.
They politely declined Yelp's services, and over the period of a month I saw a decline in their yelp ratings due to questionable reviews over very superficial stuff not indicative of overall service quality.
Idunno what to believe, but a couple colleagues know people with similar experiences. If Yelp is in the wrong here, I sincerely hope they are exposed and get the negative publicity they deserve.
I am a direct competitor of Yelp and I have to say that the 'reviews' theory just doesn't ring true with me.
Firstly at Yelp's size the chances of something like that leaking are high and the legal and reputational consequences would be catastrophic.
Secondly, there are far more effective and subtler ways of promoting the interests of their advertisers and Yelp are one amongst the less aggressive exponents of these in the industry.
If Canada is like the U.S., the median traffic speed on those roads you mentioned is greater than the speed limit. Thus it's really not a minority/extremely "can't say" opinion you're espousing, but you're right that there will usually be a (smaller) group of very vocal opponents
It's a strange dichotomy, but at least in my experience it almost seems like although most people drive faster than the speed limit, most are also instinctively against the idea of raising those limits. (Perhaps because the majority of people believe themselves to be better than average drivers.) Or maybe they believe that people will simply continue to drive faster than the limits even if they were raised, so the status quot is preferred. If that's the case though, surely there's a better solution.
