Why are cars geared so low?

[darxus]

For a given speed, the higher the gear you're in, the less gas you burn.

I can drive 30mph in my Accord in fifth gear comfortably on a level road.

I'm sure the relationship isn't entirely linear, but that should mean I'm burning roughly twice as much gas as necessary at 65mph only because of how low the top gear is.

Why?

Comments

[frobzwiththingz.livejournal.com]

Because the amount of power (i.e. gas burned per unit time) required to overcome internal engine friction (ie, whetever you would need to idle your engine at a given RPM) is miniscule compared to the power required to overcome air drag at higher speeds. The power required to overcome the air drag is roughly proportional to the *cube* of your airspeed. IE, your air drag losses at 60mph are 8 times what they are at 30mph.

Your engine also has an RPM range at which it is most efficient, and one at which it can develop the most torque. Neither of these are likely to be in the RPM range you want to use here (probably about 1500 i'd guess), unless you're planning to retrofit your car with a big-ass marine-or-locomotive-style diesel engine.