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I thought the same. In my anecdotal experience, drivers tend to get much lower than the manufacturer mileage because they optimize for things other than fuel ec
by vkjv 11y ago
I thought the same. In my anecdotal experience, drivers tend to get much lower than the manufacturer mileage because they optimize for things other than fuel economy (e.g., speed).
My dad taught me lots of tips on conserving fuel and thankfully I've exceeded the sticker numbers on every car I've owned.
- Zelphyr 11y agoCare to share some of those tips?
- nathancahill 11y agoAccelerate gradually, stay off the brakes.
- kwelstr 11y agoAnd when in the highway don't go too fast, speed increases drag etc. etc.
- lucaspiller 11y agoI did some tests on a long drive last week, for the Smart Forfour I had this was the fuel consumption. It was all along flat, straight parts of the highway. Reports were based upon the cars own fuel efficiency monitor. - 135 km/h 7.8l/100km (30 mpg) - 125 km/h 6.5l/100km (36 mpg) - 115 km/h 5.4l/100km (43 mpg) I never realised speed made such a difference! (Mpg is US gallons)
- btilly 11y agoThe reason why it matters is that air resistance is proportional to the square of your velocity. At high speeds that term dominates.
- jtuente 11y agoDue to some physics things that I don't understand, it actually ends up proportional to the cube of your velocity. source: presentation by Dr. Rizzoni at Center for Automotive Research at OSU
- semi-extrinsic 11y agoIt's actually neither square nor cubed, but you can use those approximations with varying success for different car shapes and Reynolds numbers. There are several different physical effects that together create drag: you have form drag, skin drag, interference drag, and even lift-induced drag (the last one essentially only on sports cars).
- mikeash 11y agoPower consumption is proportional to the cube. Aerodynamic drag i.e. force opposite the direction of travel is proportional to the square of your velocity. Power consumption for steady cruising is equal to drag multiplied by speed. Thus power consumption is proportional to the cube of speed.
- btilly 11y agoRight. And if you're measuring miles per gallon, you're interested in energy consumed per mile traveled, not energy consumed per second. And aerodynamic drag tells you energy consumed per mile traveled thanks to the relationship that energy is force times distance.
- protonfish 11y agoThat's - 84.0 mph - 77.5 mph - 71.5 mph For us in the states.
- deleted 11y ago[deleted]
- bayesianhorse 11y agoNo, for you in the states it's 70mph ;-)
- brc 11y agoA dramatic demonstration of this is the Bugatti Veyron. Between the original version (1,001 hp) and the SuperSport version (1,184 hp) - the top speed only increased from 408 kmh to 431 kmh. So a 183 hp increase in power yields only a 23 kmh increase in top speed - bearing in mind that 183 hp is more than most passenger vehicles have in total. It gets exponentially harder to push air out of the way the higher the speed gets.
- tremon 11y agoThis is by no means an exhaustive list, nor an authoritative one. Would love to hear other's thoughts on these: - When accelerating, try not to over-extend the throttle. If the engine is at 2k rpm, you get just as much acceleration from 30% throttle as 100%, at half the fuel cost. - Release the throttle well before you reach a traffic light/stop sign. Deceleration by engine will cause a smoother stop and gives the traffic light more time to turn green. You spend less fuel trying to reach the stop line, and spend less fuel accelerating again. Bonus points for shifting down while decelerating. - Keep tires well-inflated and oil levels up. Less friction means less wasted energy on both. - Choose the highest gear when cruising. Most cars since 1990 can do 50kmh (30mph) even in fifth gear, as long as you don't need to accelerate. - Drive slower. Most car engines are most efficient around 3500 rpm, which maps to somewhere between 90-110 kmh (60-70mph). Most highways allow for a higher speed. Diesel engines have their optimum at 2000 rpm, or so I've been told. Of course most of this works best with a stick shift. I've never driven an automatic.
- userbinator 11y agoChoose the highest gear when cruising You can do this for automatics too - you just have to learn where the shift points are and drive at the right speed. Lift up on the accelerator quickly to upshift, press it down quickly to downshift. One thing that I notice easily when riding is when the driver is constantly staying at only a few km/h slower than the shift point, causing the engine to spin faster and consume more fuel than necessary. It often means the car is louder and vibrates more too, so not a good thing overall. This is harder to do for newer models with quieter engines and smoother shifts but older automatics have very noticeable shifts and engine noise to judge whether you're near the bottom or top of each gear. It's very noticeable in larger trucks and buses. Edit: another point I'll add to the list is traffic light phasing - look far ahead and observe the timing of the lights, and adjust your speed so that you're not going too fast (you'll arrive at a light before it turns green) or too slow (it'll turn red very shortly before you arrive). Obviously, you should do this only if traffic permits, but it's a great "trick" (not so much a weird one) when you can get from your origin to your destination at a constant speed with nearly no stops.
- 11y ago
- ticktocktick 11y agoJust stay off the brakes as much as possible. No big secret really.
- enraged_camel 11y agoUnless your car has regenerative breaks, in which case you should randomly and unpredictably break to generate free energy. edit: downvoters are once again proving that HN doesn't get jokes.
- ska 11y agore: edit Have you tried being funnier?
- mod 11y agoI think it's more that HN doesn't appreciate jokes, the discussion tends away from that here. Also, from the guidelines: Please resist commenting about being downvoted. It never does any good, and it makes boring reading.
- mikeash 11y agoAs I always say, HN doesn't have a problem with humor, but it needs to actually be funny.
- frankzinger 11y agoI thought it was a decent enough joke. Tough room.
- hinkley 11y agoOne of the things I like most about my Jetta TDLie is that the DSG will downshift if you keep the brakes on for more than about 5 seconds. On long downhills I can take my foot off the brake for about half the trip down and the gearbox does the rest until the speed slowly creeps back up.
- bonzini 11y agoNo matter how careful I am, it's hard for me to get lower than 130% of the fuel consumption reported by the manufacturer. Perhaps I can do 120% of the reported consumption at 90 km/h, but I can hardly get lower than 140% on the highway (130 km/h) and in city traffic.
- brandon272 11y agoI'm the same way. Even when I drive as conservatively as is safely possible I still can't get it lower than ~120%.
- userbinator 11y agoAre you in an area with much hilly terrain? That'll definitely increase fuel consumption significantly.
- TylerE 11y agoActually, it depends. Modern cars do better in rolling hills than on perfectly flat land, since they can cut fuel entirely on the downhill, and the climbs don't require that much extra fuel over just maintaining speed. Now, mountains are another story, of course. Some good stuff in this SE question: http://physics.stackexchange.com/questions/6220/can-a-car-get-better-mileage-driving-over-hills http://physics.stackexchange.com/questions/6220/can-a-car-ge...
- aianus 11y ago> Modern cars do better in rolling hills than on perfectly flat land, since they can cut fuel entirely on the downhill This is physically impossible. Even if the car was perfectly efficient at overcoming the force of gravity on the uphill portions (which it is not), you cannot do better than flat terrain (unless by hilly you mean 'net downhill').
- adrianN 11y agoICUs are more efficient if you open the throttle more (up to a point...). So it could be possible that the extra potential energy you store going uphill at better efficiency makes a difference.
- kbenson 11y agoBut that's actually irrelevant for the cited report. What the referenced graph says is that from 2008 to 2014, auto manufacturers declared a certain increase in emissions/economy, real world people reported a different amount, and those amounted to, unique to GM in this report, a negative percentage in how well they achieved their claims. That is, on average, GM car fuel economy got worse over this period, or people's driving habits changed for GM cars. (I can't discount the possibility of something else is going on, such as an influx of a different type of car for GM over that period, I haven't read yet how they normalized the study and accounted for things like that).
- rnovak 11y agoIt's not irrelevant at all. Manufacturers report fuel consumption during a controlled environment, with specific driving habits, etc. Real world people drive insane (at least in the US), and most wouldn't even re-pass their drivers-license test, so most assuredly do not have the best driving habits. So drawing the conclusion that manufacturers are "lying" from the discrepancies between those two data sets is ridiculous.
- kbenson 11y agoIt's irrelevant because unless both a) people changed their driving habits on average over that time frame to cause more emissions and b) that change was primarily limited to drivers of GM vehicles, then driver habits do nothing to explain the data. > So drawing the conclusion that manufacturers are "lying" from the discrepancies between those two data sets is ridiculous. Perhaps you should pay attention to actually what I said, not what you think I said. I didn't say GM was lying, I implied their numbers deserve extra scrutiny.
- rnovak 11y agoThe whole controversy is over manufacturers reporting false numbers, i.e. lying. Saying a manufacturer deserves extra scrutiny can absolutely be inferred to be an accusation of them reporting false numbers, i.e. lying. My reading comprehension isn't at fault here. Secondly, it's still irrelevant. You would have to prove that an improvement at throttle position 0.10 over 5 years equates directly to an improvement at throttle position 0.40. How an engine performs in condition A has no inherent relation to its performance in condition B. So yes, I stand by what I said. Maybe before accusing people of "not paying attention", you should look at your own language and see if it's ambiguous?
- abalone 11y agoExcept some models are significantly more off the mark than others. Maybe some owner populations have worse driving habits than others, but it's worth investigating.