Question about hills

[thornburg]

Originally Posted by Ford Man

After installing a vacuum gauge in my '88 Escort I have found that it is much better to let completely off the gas going down hill than to maintain the same or less acceleration.

Are you accounting for the greater fuel required to go up the other side because you were going slower? Or are we only talking about lone hills (which are always up first then down, without another up after the down)?

I'd be curious to see some multi-run testing done by someone with one of those computer data-logging setups, testing various methods of going up & down the same hills over and over again. Of course, it would be ever better to get several sets of data (for example, DFCO behavior plays a big role in what the "best" method is).

[lowbridescape]

I aim for speed limit + 9 at the bottom of the hill and hold the LOD on the ScanGauge as high as I can. Last night I saw it hold at 99 before it finally downshifted. When it downshifts, instantaneous mileage is cut almost in half. Everything about driving the Escape around town is getting it into the highest gear possible.

The hard part is starting off uphill. There's nothing to to do but punch it to get enough speed to let it upshift. Otherwise I'm spinning uphill with mileage in single digits.

[theholycow]

Originally Posted by thornburg

I'd be curious to see some multi-run testing done by someone with one of those computer data-logging setups, testing various methods of going up & down the same hills over and over again. Of course, it would be ever better to get several sets of data (for example, DFCO behavior plays a big role in what the "best" method is).

It would probably also suffice to use average mileage over a whole tank of fuel, one tank with one strategy, one tank with the other...

[Philip1]

OK I'll step up on this one ....
We are dealing with a turbocharged car here. (boost=lots of fuel) the idea here is to keep out of the boost I think you have been doing things right if you can accelerate down the hill staying out of boost (good) and if this keeps you out of the boost going up the other side then this works. Again BOOST= bad FE

[1cheap1]

He needs a electronic boost controller, then he can turn the boost off when he wants and drive with out it. On any grade i try to put it in neutral or eoc and get as far up as i can then kick it in to the top if i slow to much. Lately thought the traffic has been so sparse i can at times slow to 40mph while p&g on the freeways. My how my thinking has changed, i look for trucks now to draft. In the past they just annoyed me to now end. This works well for overpasses and bridges. Eoc with a truck in front is the best.

[trollbait]

Originally Posted by 67 Satellite

I usually just keep my right foot steady and let the car pick up speed down the hill then let it slow slightly on the up hill side.The speeds are kept within reason though and there aren't that many big hills around here anyway.I try to keep it less than 10 m.p.h over the limit and 5 m.p.h. under.

This is refered to as driving with load (DWL). Keeping the engine at a set load or throttle position is more efficient than varying it, outside of pulse and glide that is.

[WhitePolarBear]

Talking about hills, what about cruise control? Should I disengage the cruise control? We don't really have "hills" in coastal Texas, unless you call the overpass "hills".

[KARR]

Originally Posted by R.I.D.E.

Your total energy use, will be lowest if you avoid speeds above your desired average. This is becasue of the exponentially greater aerodynamic drag at higher speeds.

Of course if your speed increases as you coast down the hill that additional speed costs you no additional fuel. The question is the risk of a traffic violation as well as your personal safety.

Note (coasting by my definition is always in neutral)

Most of the hills here are very small grades, so there is no possibility of dangerous speeds.

In a perfect scenario, your hill would be the perfect grade and you could maintain the same speed regardless of whether you were going uphill or downhill.

Remember aero drag is by far the greatest source of energy losses at high speeds, close to 2/3 at 65 MPH.

That is why my strategy is to try to maintain the same speed.

regards
gary

I've done a search trying to find the exponential dependence of drag with speed but I didn't find it. The only formula I know is



Can you tell the formula of the exponential dependence please?

[lowbridescape]

It's the V squared part. Drag is proportional to velocity squared.

[trollbait]

Originally Posted by WhitePolarBear

Talking about hills, what about cruise control? Should I disengage the cruise control? We don't really have "hills" in coastal Texas, unless you call the overpass "hills".

On flat roads, using cruise control is DWL. My parents live in such an area of NC, and using cruise will usually net above EPA. It won't be the numbers using extreme hypermiling methods, but it's easy and reliable. On hilly terrain the cruise control can hurt milage. It tends to be more aggressive trying to maintain speed, and won't take advantage of downhill coasts.