Pulse and Glide with hills
 

What is the most efficient when PnGing through rolling countryside:
Pulse up the hills and glide down, or
Pulse down the hills and glide up?

Pulse up, glide down. Average speed should be about the same but your peak speed will be less.

Hill or no hill I just pulse when I get to the lower speed limit I wish to hit and glide when I hit my max speed. I have yet to hear why it would be more efficient to do it one way versus another, but am open to hearing any that you guys have.

It's just one more way to keep the engine running at the best BSFC. You can "pulse" at that optimal rpm/throttle position, without changing speed. You get the same benefits, but without the air drag of the higher peak speed, or the crazy speed variations. Instead of building kinetic energy, you're building potential energy.

Seat-of-the-pants testing I've done shows this to be the better choice, for my car, in my area with the hills we have. My best highway run - 75mpg for 150 miles - was using this technique. Pulse from the bottom at ~45mph to just before the peak at ~60mph, glide up and over and down.

It seems to work better for manual than for automatic, though. I think DWL is better on hills for automatic.

I'm inclined (sorry :)) to agree with you, but let me play the devil's advocate, for the sake of argument. 'Pulsing up' contradicts the 'ride like a cyclist' mantra. It puts more of a load on the engine, further decreasing efficiency. Is the 'glide down' enough to compensate?

I'd say DWL / bicycle / roller coaster driving would be the intermediate level technique, and maybe the best for an automatic that likes to downshift with high load. Pulse up, glide down would be the next level, and better suited to manual transmissions.

I agree with PaleMelanesian.

You're right that some of the tips on the big list are contradictory. The differences are mostly related to whether you're doing mild, medium or hard core.

When the list was produced, we also tagged each tip with ratings for difficulty/skill level (but I haven't incorporated into the output yet). They would show that the contradictory tips are in different categories.

A higher peak speed (pulse down) would mean more of an aerodynamic penalty, right?

I've been struggling with the same question about p&g vs. hills. My commute has quite a few of them. I don't have the definitive answer due to a lack of testing instrumentation, but I've been experimenting with the technique. I approach each hill a little differently based on it's steepness. If it's shallow I just pulse up the hill and glide down, initiating my pulse well before the hill so I can gain most of my momentum before I get to it. There are a couple areas where I shorten my glides and initiate my pulse early on the downhill to make the most of gravity and cheaply grab some extra momentum. For steeper hills, I will initiate my pulse early, grab momentum and let it bleed off as I climb the hill. I maintain the same throttle pressure for the pulse throughout the climb, gearing down if necessary. When I crest the hill, I continue the pulse, using gravity help regain my momentum and initiate a coast once I'm up to speed. It makes for a longer pulse and sometimes a shorter glide, but usually I can make up for it later in the trip. My favorite sections involve long downhill runs where I can kill my engine and coast for a little over a mile.

This is all seat of my pants type of stuff, so I can't really tell you if I'm on the right track with this technique, especially because I'm very new to the concept of p&g driving and I definitely need some more practice to get it right. On the other hand, I did get about 25mpg out of the last tank. Given that the updated EPA combined rating on my truck is 16mpg, I must be doing something right. :thumbup:

[QUOTE=Twerp;31598]I've been struggling with the same question about p&g vs. hills. My commute has quite a few of them. I don't have the definitive answer due to a lack of testing instrumentation,
Right. I'm in the same situation. Haven't installed the vacuum gauge in my '88 Accord, but encounter several miles worth of rolling terrain on my daily commute. With back-to-back hills, there's opportunity to use either strategy, so it's not just a philosophical exercise.

My thinking is that pulse up/glide down is better, because the fuel savings is achieved in the P&G technique by the glide phase. So extending or maximizing the glide would be more beneficial.
And sickpuppy has a good point about the aerodynamic penalty of pulsing down.
P&G may be an 'advanced' technique, but it's accessible immediately, unlike waiting for the weekend/spare moment to install the vac gauge to DWL.

Just have to point out that the above isn't true all the time, or maybe anytime for some of us. If your car has the HP to stay under 75% throttle in top gear going up the hill, it is more effecient to run the engine like that than drop a gear and use 35% throttle with more rpm. I didn't believe this until I got my scangauge but it shows that to be true.

I love P&G with hills, my 50.5km commute this morning had an average speed of 71km/h with a max of 110km/h gliding down a big hill, the speed limit is 80km/h. I got 6.0L/100km, 39MPG out of an automatic 95 Neon in light traffic.

The hills allow me to P&G in some traffic and get me to work with out any extra time and get nearly 1/3 better mileage(I use to average about 30mpg on the same route). I should note that this is engine on gliding too.

I have a couple of different route options that I can use. Some with more hills but more stops as well. The route I used today has the fewest stops and is in the middle for hills and is probably my most efficient route, sometime I'll have to try the hilliest route but it will take significantly longer but it might be the most efficient.
Ian

Where the bicycle analogy breaks down is when you consider BSFC. Human legs are most efficient at any range of output. Car engines have a very peaky efficiency chart - very different. Driving the terrain like a biker is good, but P&G is better, because of this fact. If the car's engine was efficient over its whole range, it wouldn't matter. Metro can probably verify this with his Electric. ;)

I could verify it if I had onboard energy consumption instrumentation... which I don't, unfortunately.

:( sorry. For you and for us.

If you want to do a fun and educational experiment, do it on a bicycle.
You can wind thru your gears with less energy expenditure and peddle more efficiently going down hill. IMHO

Sure - and drag is something you can't ever recover.
Drag, mechanical or aerodynamical, is permanently lost energy.

It really depends on the grade and length of the hills. My local area has hills like Interstate overpasses. The hills get steeper when I go west. I've done a lot of local driving, basically living here for almost all of the 40+ years I've been driving. With the Fiesta's factory MPG gauge as well as the ones on my Altima and CVT first gen Insight (both sold and gone) I have developed some tricks to utilize hills for better mileage than perfectly flat ground.

Very gradual acceleration (in top gear) cost very little in additional fuel consumption. If the hill allows you to maintain your coasting speed then hit the top of that hill at the speed limit. That's about the steepest hill here, very few will allow the vehicle speed to increase above 45 MPH, so on any congested road I look for some drafting help to maintain my coast above 45 MPH.

Some hills require a completely different tactic. Thes are short duration but slightly steeper hills. On these I will gradually accelerate approaching the hill and go neutral coast up the hill and regain my speed downhill. My highest speed is close to 60 MPH (55zone) and at the crest of the hill that speed will drop to 40 MPH. This avoids the hit in fuel economy I would see if I just let the hill increase my engines load trying to maintain a constant speed. I regain most of my speed coasting on the down slope of same hill.

Other very shallow hills I will P&G on the upslope and even sometimes on the downslope. Again I am using very gradual acceleration, like 10 seconds to increase my speed by 5 MPH (faster on the downslope). This allows me to avoid any 10 MPH over situations where the roads are heavily monitored by the local police, while also not being too great an impediment to traffic.

In every instance I try to maintain a speed of over 40 MPH. In the Fiesta that is where it goes into 6th gear. I also try to avoid any load where the transmission shifts out of 6th gear at speeds over 40 MPH.

My speed peak and low points depend on surrounding traffic. If it's heavy I look for a big rig to fall in behind and pulse-draft. If lighter then I increase my speed differential range, but in both cases I try to avoid impeeding traffic flow. If someone wants to plant their nose up my rear end this tactic also serves to frustrate them enough so they pass me, just thinking I am an old geezer who can't drive worth a darn. Little do they know.

All the cars in this response were automatics. I need one in case the wifes car becomes undriveable for any reason, and with the congestion here you avoid crawling through a 1 mile 1 hour nightmare in a manual.

regards
Mech

It would seem that you are typically going to be staying in lower gears while pulsing/burning up a hill where you can quickly gain speed and get into higher gears while pulsing down a hill.
It is my contention that the car is more efficient gaining speed in a higher gear while going down hill thus storing inertia for the coming hill climb.

Here on the big island we will drive from Hilo to Kailua-Kona over Saddle road but in that case you have to just get up that mountain getting poor mileage but then you get to coast for miles and mile on the other side.

The method you describe is not correct for most situations. You want to hold the highest gear possible that allows you to travel at a reasonable speed up the hill. This might mean pressing the throttle about 80%. It is more efficient than downshifting and using less throttle opening. Coast the downhill portion and supply some pulses if the grade isn't steep enough to maintain the speed you want. Much easier to do with a manual transmission.

Going over a mountain pass is very efficient since it acts like a long pulse and glide. You pulse up the mountain, and glide down the backside. I did this recently going from Montana to Oregon through some passes. My car is geared low, so I could hold 65mph in 6th gear going up, and then neutral coast on the backside. If only I had an engine kill switch, my economy would have been even better.