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I have a 2010 model car and I still seem to get significantly better gas mileage around 55-65 mph than I do around 70-75, although I haven’t measured it scienti

I have a 2010 model car and I still seem to get significantly better gas mileage around 55-65 mph than I do around 70-75, although I haven’t measured it scientifically. Isn’t this a function of wind resistance physics that can’t be solved, just mitigated? As driving automation increases and the threat of climate change and CO2 emissions looms larger, automated cars could drive at current speed limits without getting impatient like a human driver, improving both efficiency and safety.

lm28469 7y ago
It does. Almost any car will be more efficient around 50-60mph. But it only matters on highway where the bottleneck is due to aerodynamism, at lower speed you might be less efficient at 20mph than 30mph for example. https://en.m.wikipedia.org/wiki/Fuel_economy_in_automobiles https://en.m.wikipedia.org/wiki/Fuel_economy_in_automobiles
ska 7y ago
Isn’t this a function of wind resistance physics that can’t be solved, just mitigated? Yes, this is fundamental; roughly power required is proportional to cubed velocity. Improved coeff of friction helps, but you can't get away from this. Eventually air friction is the completely dominant force. So at highway speeds, absent some rare gearing issues causing inefficient fueling, faster means less efficient. This is also why the fastest "hypercars" are pushing on order of 1000 hp. At lower speeds, all sorts of other issues kick in (and idling is its own issue)
- mywittyname 7y ago
  A demonstration of this fact can be found in a list of fastest production cars in the world: https://en.wikipedia.org/wiki/Production_car_speed_record https://en.wikipedia.org/wiki/Production_car_speed_record The RUF (Porsche) needs 460hp to break 213mph. The next record breaker needs 618hp to break 221mph. The 241mph record is made with 806hp. This continues incrementally until the current record holder, which needs 1350hp to hit 278mph. It took three times as much power and three decades of computational advancement to build a car that could go a mere 65mph faster than the 1983 record breaker. Side note: the listed horsepower numbers before 1980s are basically made up. You can safely assume SAE J2723 horsepower (what cars use today) is ~60-75% of published value for cars older than 1980 (and about ~80-95% for cars between 1980 and 2005).
rtkwe 7y ago
It's a bit of both but yes velocity dominates the drag forces. You can reduce the wind resistance of vehicles reducing their coefficient of drag but the dominant factor as you reach higher speeds is velocity which increases as a square where the drag coefficient is only directly proportional to the end drag. There are definitely limits to how low drag we can make the normal passenger sedan without drastically changing it's functional form. If we move to a more infrastructure style car transport where you just subscribe or have access to (depending on where we end up on the public-private spectrum) there's probably a lot of gains we can still make that will make cars much uglier (to our current eyes) but more aerodynamic.

lm28469 7y ago

It does. Almost any car will be more efficient around 50-60mph. But it only matters on highway where the bottleneck is due to aerodynamism, at lower speed you might be less efficient at 20mph than 30mph for example. https://en.m.wikipedia.org/wiki/Fuel_economy_in_automobiles https://en.m.wikipedia.org/wiki/Fuel_economy_in_automobiles

ska 7y ago

Isn’t this a function of wind resistance physics that can’t be solved, just mitigated? Yes, this is fundamental; roughly power required is proportional to cubed velocity. Improved coeff of friction helps, but you can't get away from this. Eventually air friction is the completely dominant force. So at highway speeds, absent some rare gearing issues causing inefficient fueling, faster means less efficient. This is also why the fastest "hypercars" are pushing on order of 1000 hp. At lower speeds, all sorts of other issues kick in (and idling is its own issue)

mywittyname 7y ago
A demonstration of this fact can be found in a list of fastest production cars in the world: https://en.wikipedia.org/wiki/Production_car_speed_record https://en.wikipedia.org/wiki/Production_car_speed_record The RUF (Porsche) needs 460hp to break 213mph. The next record breaker needs 618hp to break 221mph. The 241mph record is made with 806hp. This continues incrementally until the current record holder, which needs 1350hp to hit 278mph. It took three times as much power and three decades of computational advancement to build a car that could go a mere 65mph faster than the 1983 record breaker. Side note: the listed horsepower numbers before 1980s are basically made up. You can safely assume SAE J2723 horsepower (what cars use today) is ~60-75% of published value for cars older than 1980 (and about ~80-95% for cars between 1980 and 2005).

rtkwe 7y ago

It's a bit of both but yes velocity dominates the drag forces. You can reduce the wind resistance of vehicles reducing their coefficient of drag but the dominant factor as you reach higher speeds is velocity which increases as a square where the drag coefficient is only directly proportional to the end drag. There are definitely limits to how low drag we can make the normal passenger sedan without drastically changing it's functional form. If we move to a more infrastructure style car transport where you just subscribe or have access to (depending on where we end up on the public-private spectrum) there's probably a lot of gains we can still make that will make cars much uglier (to our current eyes) but more aerodynamic.