hill driving techniques

[MetroMPG]

<img src="http://www.co.larimer.co.us/engineering/traffic/W7-1.gif" align="right" width="100">

i want to start a thread to talk about the finer points of driving efficiently in hills.

the first time you watch instant fuel consumption data on a trip computer or OBD gauge when transitioning from a flat road to an incline, you may be surprised at the magnitude of the mileage hit.

to drive a typical car at 70 mph (115 kph) takes about 20 kW (27 hp). A barely noticeable 1% uphill gradient increases this by 5 kW (25%), with a corresponding increase in fuel consumption. - source

why? because now, not only is your engine working to overcome rolling & wind resistance, internal & driveline friction, but in addition it's also effectively lifting the weight of the vehicle up the slope.

techniques

the most commonly espoused method is to accelerate gently, on the flat, just before the hill. then let your speed fall off as you climb. the goal in this technique is to "drive for load": don't ask the engine to do any extra work, instead, bleed off momentum while going up.

but let's take this thread to another plane (pardon the pun)...

finer techniques

<ul><li> need to accelerate, and approaching a descent? save your strongest acceleration for the downhill.</li>

<li> i generally don't draft (i prefer good forward visibility), but the one place i break my own rule is on long up-hills on the freeway. if i get passed by someone at the right time, i'll speed up and tuck in behind for the ascent</li>

<li> big/steep descents offer the option to glide/coast in neutral with the engine off (or on - you decide). this is apparently illegal in some jurisdictions. (i've wondered why - was there once an epidemic of coasting crashes? or is it a throwback to the days of drum brakes and the risk of overheating them instead of using engine braking?)</li>

<li> the furthest i've ever coasted down a hill with my engine off was on the downhill side of a pass in the rockies on my way to vancouver in my old accord: something like 12 kilometers. i won't tell you how fast i got going (there was little traffic)</li>

<li> assuming you don't glide/coast, what's more efficient at a constant speed: driving 2 miles on a flat road? or driving 1 mile up a grade, and then 1 mile down an equal decline?</li></ul>

discuss amongst yourselves...