🚀 go-pugleaf

cml@cs.umd.edu (Christopher M Lott) writes:
> I believe that the magic number of 55 has something to do with
> wind resistance.  I was told that wind resistance increases much
> more rapidly past 55 than below it.  Apparently resistance doesn't
> rise linearly with speed - any aero engineers that can support or
> debunk this fact/myth?  

I believe that drag varies proportionally with the square of the
velocity, and that drag exceeds other sources of friction at abut
25-30mph for most cars.  Most modern cars have pretty low drag
coefficients, though, and there's not much of a "knee" in the drag curve
at freeway speeds.  Another factor which can have a significant effect
is how the engine is geared.  Engines are most fuel efficient at a
particular point on their power curve; the point of greatest fuel
economy is generally where the engine is running at this point in its
highest gear.  On my Toyota Camry (4-speed automatic), for example, this
seems to be at around 65mph on flat stretches of freeway.  I wouldn't be
surprised if many cars were "optimized" for 55, though.


Amanda Walker						      amanda@visix.com
Visix Software Inc.				    ...!uupsi!visix.com!amanda
-- 
Don't try to out-weird me... I get stranger things than you free with my
breakfast cereal.