I want to straighten out some contradictory mpg tips...
 

I drive a 2012 Ford Focus, 2.0 liter, automatic...if that's helpful.

1) What is generally a good mph "sweet spot" for optimum gas mileage? I've heard 40, 45, 50, 55 and 60.

2) Should I build up speed gradually (an old classic) or get up to desired speed fairly quickly?

3) On flat or minimal grade roads, is a skillful pedal foot preferrable to cruise control? The old, classic viewpoint was that cruise was better, but I've been hearing differently. Thanks in advance for your help.

1) It depends on the car and engine. If the engine is relatively efficient throughout the rpm range, then the lowest speed in the highest gear is often the best, due to aerodynamic drag (which increases quickly with speed). If the engine is particularly inefficient at low load, then a slightly higher speed would be better. There is no single speed which is good for all vehicles & engines.

2) I personally build up speed in the middle of the load range, keeping away from 90%+ of full throttle. In theory on my engine, the load range 85-90% would be best for economy under acceleration. But I also try to avoid stressing the transmission, and the closer you go to max torque, the more stress you are putting into the clutch & gearbox.

3) It depends on the driver. If you have a very steady right foot (keeping load not speed steady), it will beat the cruise.

Of course, in an automatic car you are not in control of the gearbox, so you have to drive in a way that encourages the car to be in the highest gear possible (i.e., gentle acceleration).

Be aware that most MPG advice relates to manual cars only (since torque-converter automatic gearboxes are horribly inefficient).

1. Certainly no significant improvement below 50mph, above about 60mph aerodynamic drag increases much more quickly, depending on how aerodynamic the car is, gearing, & at what revs the majority of the torque is produced by your engine (see if you can find a power & torque graph for your cars engine).

Here's a couple of graphs showing aerodynamic load vs speed giving you a rough idea. https://www.speed-wiz.com/graphs/aero-drag-graph.htm https://www.kasravi.com/cmu/tec452/ae...ehicleAero.htm

And TBH anything below 55mph is impractical/inconsiderate on any BUSY motorway/highway as trucks would have to pass you causing ques & slowing down other traffic, at least on 2 & 3 lane ones anyway.

Anyway, basically you want top gear with the lowest revs that is still IN the main torque 'curve'.

2.Gradual build up for diesels (they have no throttle plate), short low rev 'bursts' of about 3/4 throttle for petrols with a conventional throttle plate (electric or mechanical).

Although be aware some petrols don't have a throttle plate either so those might be better with a gradual build up (although they still produce a vacuum in the cylinders, that's what wastes power).

Also bear in mind theirs no point quickly building up speed if you've gotta slow down several seconds latter!

3. I hate people who slow down & speed up on motorways! Grrr lol. Letting your speed drop by not giving more throttle going uphills will improve MPG vs steady speed (whether manual or cruise control) but it's a PITA to everyone else!

For steady speed, cruise control is better as it naturally won't let you overspeed downhill. Although with any auto you may well have to manual select top gear to stop the stupid box downshifting unnessacarily (as my 325 did!). Obviously don't let the revs drop too low going off the torque curve (re earlier comment).

MMUK

Don't forget on most autos you can manually select gears. Although if you did that all the time it would kinda defeat the point ;).

Btw most stress occurs on the clutch during pulling away as its (naturally) slipping, or in rough gear changes. Once the clutch is fully engaged it makes no difference how much throttle you give it (assuming it's not slipping due to being oil contaminated, worn out or its max torque limit being exceeded by large torque increases from remapping excessively etc).

I really wouldn't worry about the torque going through your gearbox, lol. Unless you know it's on its last legs, is an inherently weak box or again the engine has had a large torque increase then it won't make any significant difference to box life avoiding peak torque.

> ... or again the engine has had a large torque increase ...

Well, a +30% remap and also a 6th gear added (+28% higher than my original top gear 5th). So in combination +66% extra torque going through the box if I floored it in the new top gear.

I don't remember being able to select specific gears (other than the towing gears) in the two autos I've driven myself (both short-term hires). Is this a common ability in torque-converter autos?

& I can pretty much guarantee that the oil is good in mine :-) Changed 3 times this year for one reason & another.

My transmission is actually a 6-speed, dual-clutch automatic w/manual mode. I've heard it also described as an automatic manual; not your standard automatic transmission, if that extra information might help. Thanks again, everyone.

In that case ... keep it in either manual or 'eco' mode, and try to keep your RPMs down. You can use either the gentle acceleration or quick acceleration technique since the gearbox should support both.

Unfortunately, I don't know how to drive a manual.

>Unfortunately, I don't know how to drive a manual.

In that case, you're back to the 'gentle acceleration to keep it in a higher gear' technique.

If you learn to use it in manual mode, you will probably enjoy driving the car more since it is more responsive that way.

Dont know how to drive a manual? Jesus, its not exactly hard now is it?

That's not really fair Paul, you know auto boxes are dominant on the other side of the pond...

Yea but I still dont get why!

@ Draigflag: Easy there, mate. As MMUK said, automatics using regular unleaded gas are predominant over here in the states. For one, regular gas is less expensive than diesel; part of the reason that, with the exception of VW, diesel cars are not widely available over here. Secondly, we Yanks are a hard working lot, myself included. 50 hour weeks and beyond are not uncommon. So when we're having to deal with a long commute during "rush-hour", the last thing most people want to deal with is having to downshift constantly with the traffic being insane. They want to just put it in drive and go, without having to think about it any further. My "driving fun" comes when I save money on gas at my fill-ups. I dig being able to keep more money in my wallet while the dummies driving like idiots and getting 13 mpg. If this helps my gas-mileage "street-cred", I'm averaging around 42 mpg (US) so far with my automatic Focus. My mpg driving style is still a work in progress. Any tips as to how I can get better at it are always helpful. Thanks.

Not sure about the features that your trip computer can display, but a handy one to monitor is the 'instant mpg' function. This is a handy tool to adjust your driving habits.

If you don't have that function, here is a great tool that can help out...

https://www.scangauge.com/products/scangaugee/

Myself and a few others have these... they have a heap of other functions that monitor the cars general 'health' as well.

6 speed auto....

Many cars I drive are 5 & 6 speed autos. I found there is no need to have the car in 'D' when driving around town at speeds up to 50km/h, the cars run much better when selected in 3rd gear, which also eliminates the tranny changing up and down between 3rd and 4th constantly.

They still operate through the gears up to 3rd with no problem.

In your case the car may sit better in 4th, it all depends on the ratio set up, you might want to experiment a bit.

42 mpg.... I reckon you're doing well already.

Anyway....best of luck mate.

I'll have to disagree with the 50+ hours and the commute, while that may be true for some I think the real reason is that we are generally fat and lazy.

Most everyone is to busy stuffing cheeseburgers down their throat while chatting on the cell phone to shift gears manually.

My VW is the first auto (DSG) I've had in 20 years, I love manuals but am getting older and am starting to enjoy the simplicity of just dropping it into D and not worrying about it.

I think you nailed it. I try not to offend, everytime I say somthing negative about the Americans, I get called a racist?! Like we dont have traffic in the UK, this tiny Island with 62,000,000 people crammed on it and millions of cars!

It might be fun to beat up on Americans all, but the reality is that you just can't get a manual in a lot of vehicles over here ( I don't count that auto stick crap), and haven't been able to for a long time. I suspose a lot of people have just gotten used to automatics. Agreed though, I still find it really odd when I run across someone who can't drive a standard. The diesel situation is even worse, there just aren't many options for what ever reason. FYI, I always pick manuals and diesels when possible which aint' too damm often in the vehicles I wish to drive.