It's been my experience that revving as low as possible in cities and shifting down only the revs drop really low can help a lot.
A couple of weeks ago I drove about 200 km trip which involved 3 cities with somewhat dense traffic, a country road with a bunch of villages and about 90 km of highways. I drove at 160+ km/h on the highways and sticked to the speed limits in cities revving as low as possible. Combined with some other usual economy driving tricks I managed to keep the average consumption at 7.2 l/100 km (when I set off it was at 6.8).
well i drive like that this week, and then i go refill...gonna have a result then.
too bad my car has only 5 gears, means i have to go over 2k to go 100 kmh
Yeah, tell me about that. The car I've been trying out this ultra low revs technique in (2008 Corolla 1.6 petrol) revs 4k at 130 km/h on 5th. I can't imagine what an eco-beast it could be if it had a long 6th (or at least less rally-like 5th and 4th). It's nice that it can cruise on 5th at 50 km/h and still accelerate from there, but at highway pace it's more like Humvee consumption wise.
If we're talking about fuel economy, the thing to look for in all this is BSFC (brake specific fuel consumption). What you can try to do is find a map for your engine like these:
Essentially as you move upwards on the graphs you're increasing throttle. Not exactly on these graphs, but that's the general trend. What you want is to have the smallest number possible so you're using the least amount of fuel per horsepower. Climbing a given hill at a given vehicle speed requires a given amount of power. At that speed you want to pick a gear that plops you at the "right" engine rpm and below full throttle.
From these graphs the lowest BSFC is not at full throttle at any rpm (fairly close though in many cases), nor at part throttle at very low or very high rpm. It's somewhere in the middle. Generally it's going to be somewhere around the torque peak RPM of the engine. So if you need full throttle to get up the hill, downshift until you're well over half throttle.
In the first graph, the Ford 2.0L Zetec, you'd want to run the engine somewhere in that 245 loop between 1500 and 3000 rpm. The next graph for the Geo Metro would do best at around 3000 rpm. The next engine does best at 4000 rpm. So it can vary quite a bit from one engine to the next.
Looking at this from the perspective of engine wear probably yields a similar approach. If climbing a certain hill requires 50hp, choosing a gear that doubles the engine rpm and lets you ease off the throttle to maintain the same power level will cut the engine torque in half. So there might be less strain on part of the drivetrain. Then again, with the engine speed increased you'd increase wear while the reduced torque reduces it. Which one wins? Not sure. Probably there's a trend something like the BSFC curves where if you plotted engine wear as a function of throttle position or torque versus engine speed there's be a range somewhere in the middle rpm where the wear is lowest. That's just a guess on my part though.
I'd be more concerned with fuel consumption probably. If you're doing a good job of fuel consumption you're probably doing a pretty good job of managing the wear too. Keep the engine somewhere around the torque peak and you'll be doing just fine. Don't try to lug it up at full throttle though.
I voted "a few more revs with a bit less throttle," although the correct answer depends on your starting point. It could go either way
If you'r having to accelerate (in town, highway etc) and you need to apply alot of throttle use the torque band but if you maintain a constant speed use less throttle and higher gear.
Isn't the best BSFC at peak torque? In which case, as has been said, you need to be at peak torque. But drag increases nonlinearly, so that rule isn't necessarily actually true. Lower revs and less drag might outweigh peak torque revs and more drag.
a friend of mine who is studying automotive engineering once said that the typical N/A car engine, which has the throttle valve relatively close to the inlet ports, is working most efficient at peak torque rpm and ~95% open throttle, which creates a swirl effect. Same reason some modern engines how so called tumbler valves (Subarus, Audi etc idk)
This is what I love about the VW 1.8T. The torque (173 ft-lbs) peaks at 1950 RPM and holds level until around 5000 RPM. I can't stand having to rev a wimpy 4 banger near redline in normal every day driving.
If I find a hill in front of me, I just give some throttle. If I find 3 cars in front of me being driven by snailmen and I want around them, I just give some throttle. Every other car I've ever owned, I'd have to drop at least 2 gears and set myself up for an overtake (meaning getting the RPM up from downshifting and leaving some space to start accelerating well before the passing area to be able to complete the pass.) My Jetta, I typically just leave her in 5th and just press the throttle. If I would drop a gear at 45 mph, I can be well over 100 if I'm overtaking a car very easily and that is overkill. Doesn't matter if I'm heading uphill, downhill, or level.
Gets me into a bit of trouble though, since I have several big, steep, and long hills I commute to work on that previous cars I would have to drop a gear or two down just to hold constant speed. In the VW, it is too much fun to ease down on the throttle and accelerate with ease in 5th from about 2200 RPM up the hills.
In my experience the most important thing is that you don't stop the car unnecessarily. Braking is, of course, wasted energy, and accelerating the car again uses a lot of fuel no matter how you do it. Reading the traffic a long way up the road is a key to economical driving imo.
