Objectives of a drive, and fuel economy

[trashbat]

I've been experimenting this week, and going for the highest gear possible at steady speeds; so 30mph can be in fifth. Obviously this means unresponsive throttle and is in some ways akin to coasting.

The result was a nearly 10% economy gain, measured over a tank and at the pump. An average of 29.4 up to 32.2 mpg.

I think I applied it reasonably and appropriately, and although it was not optimum in terms of control, I don't think it always mattered. I wouldn't try it on a test though.

It got me thinking about how, along the lines of adapting your drive to make progress, you might pursue fuel saving as the aim. Obvious maybe, but there we are.

What do you guys regarding flexibility, especially for economy? Where are your boundaries?

[7db]

If you want fuel economy, don't use the brakes, and cruise below 50mph. Gear doesn't make a huge amount of difference.

I'd rather work ten more minutes in order to pay for the the extra gallon and have to use the brakes.

[Ancient]

My car is one which constantly suggests getting to the high gear ASAP. At times it makes sense, at times not. As a practice I find it fine but it takes more concentration than does keeping in a flexible gear and if you are thinking about something else you can be caught out (can't I Gareth?).

IMO it certainly has a place in AD, you need to watch for degree of slope in the hill ahead as much as for other hazards (i.e. slighter slopes are added to the list of 'hazards' that will affect your driving plan). It can mean more gear changes because using a flexible gear you would have handled that slope / coped with the narrowing of the road in the same gear whereas you need to consider if cruising in the higher gear is still appropriate or not.

[GJD]

I've been experimenting this week, and going for the highest gear possible at steady speeds; so 30mph can be in fifth. Obviously this means unresponsive throttle and is in some ways akin to coasting.

The result was a nearly 10% economy gain, measured over a tank and at the pump. An average of 29.4 up to 32.2 mpg.

I think I applied it reasonably and appropriately, and although it was not optimum in terms of control, I don't think it always mattered. I wouldn't try it on a test though.

It got me thinking about how, along the lines of adapting your drive to make progress, you might pursue fuel saving as the aim. Obvious maybe, but there we are.

What do you guys regarding flexibility, especially for economy? Where are your boundaries?

I think my boundary might be described by the bit of your post I've highlighted. If your sub-optimal control did not always matter, doesn't that imply that sometimes it did matter - i.e. you had less control than you perhaps should have had? Not having the control when you don't need it is one thing, but I've found when I've tried driving in a higher gear with fuel economy in mind that it can make me subconsciously accept higher speeds than I ought to when driving around and through hazards - there's not as much variation in speed as there should be.

Recently I've been trying to make myself more readily prepared to use a lower gear in 30s. Between hazards that aren't too far apart, even if I will get up to 30 between them I might stay in a lower gear up to 30 and back down again. If I have got up towards 30 and gone up a gear, I'm trying to be more decisive about changing down if the next hazard demands it. I'm trying to think more "will the lower gear cope with this one - if so, then use it" rather than "can I get away with the higher gear for this one". In my car that means I'm usually in 2nd or 3rd in a 30. That's been driven by a desire for better control around hazards, irrespective of factors like progress or fuel economy which, for me personally, are secondary.

[Gareth]

If you want fuel economy, don't use the brakes, and cruise below 50mph. Gear doesn't make a huge amount of difference.

I'd agree with this. I'm not convinced that changing up to a non-responsive gear whenever there is no load on the engine makes a huge difference to fuel economy even if that's the algorithm used by newer automatic gearboxes.

If you do avoid using the brakes then, with some cars, there seems to be an advantage in changing down a couple of gears when the engine approaches idle speed. This retains the fuel cut-off for longer, and from a fuel economy point of view it is clearly better to rely on the lesser frictional losses of engine braking rather than depressing the clutch, (forcing the engine to use fuel), and using the foot-brake.

[trashbat]

I should clarify a few things. I already do avoid the brakes and the only change here is gear selection; although this does mean being able to go further off the throttle. It's also mostly urban and rural, so little motorway cruising, which I can't do anything about except slowing. I haven't really done that this week, although I did have a few miles of it.

[trashbat]

I think I applied it reasonably and appropriately, and although it was not optimum in terms of control, I don't think it always mattered. I wouldn't try it on a test though.

I think my boundary might be described by the bit of your post I've highlighted. If your sub-optimal control did not always matter, doesn't that imply that sometimes it did matter - i.e. you had less control than you perhaps should have had?

I probably should have written 'always matters' rather than in the past tense. I only used it when I felt the situations warranted it; e.g. a straight 30mph road with no obstructions ahead. I think being able to perform unplanned acceleration to mitigate trouble is valuable in certain contexts, but I find it hard to identify where that'd apply in an urban 30.

Not having the control when you don't need it is one thing, but I've found when I've tried driving in a higher gear with fuel economy in mind that it can make me subconsciously accept higher speeds than I ought to when driving around and through hazards - there's not as much variation in speed as there should be.

Yeah, I think this is true. Again, coming off the throttle doesn't produce the same results as it did, and you don't honestly adapt accordingly. I don't find it hard to match a conscious target speed though.

Recently I've been trying to make myself more readily prepared to use a lower gear in 30s. Between hazards that aren't too far apart, even if I will get up to 30 between them I might stay in a lower gear up to 30 and back down again. If I have got up towards 30 and gone up a gear, I'm trying to be more decisive about changing down if the next hazard demands it. I'm trying to think more "will the lower gear cope with this one - if so, then use it" rather than "can I get away with the higher gear for this one". In my car that means I'm usually in 2nd or 3rd in a 30. That's been driven by a desire for better control around hazards, irrespective of factors like progress or fuel economy which, for me personally, are secondary.

This is one of things that I've changed most since passing DSA. When starting out, I used to regularly get the improved economy figures, but a combination of AD and general realisation about making progress has changed things a little.

[GJD]

I probably should have written 'always matters' rather than in the past tense. I only used it when I felt the situations warranted it; e.g. a straight 30mph road with no obstructions ahead. I think being able to perform unplanned acceleration to mitigate trouble is valuable in certain contexts, but I find it hard to identify where that'd apply in an urban 30.

I can't think of an example off the top of my head either. But the control a lower gear gives you isn't just the ability to accelerate. I don't have my copy of Roadcraft to hand to quote, but it talks about the accelerator being a control you can use to slow the car down as well as speed it up. As I descend through the rev range, I find that the ability to reduce speed with the accelerator drops off more than/earlier than the ability to increase speed with it.

[zadocbrown]

I've been experimenting this week, and going for the highest gear possible at steady speeds; so 30mph can be in fifth. Obviously this means unresponsive throttle and is in some ways akin to coasting.

The result was a nearly 10% economy gain, measured over a tank and at the pump. An average of 29.4 up to 32.2 mpg.

I think I applied it reasonably and appropriately, and although it was not optimum in terms of control, I don't think it always mattered. I wouldn't try it on a test though.

It got me thinking about how, along the lines of adapting your drive to make progress, you might pursue fuel saving as the aim. Obvious maybe, but there we are.

What do you guys regarding flexibility, especially for economy? Where are your boundaries?

How certain are you that this was a fair test? What proportion of this gain in economy might be down to other factors? I don't know.

Looking at the general approach behind your experiment.... Personally I think it's illogical to buy a poky car then drive like a grandad to get a few more mpg. You'd be better off getting a more economical car and driving it normally.

The method of driving espoused by most of us here doesn't claim to be the most economical any more than it claims to be the fastest. We are looking for a safe, systematic, smooth and progressive drive. Economy can be put into that equation as a trade-off alongside 'progressive'. The balance between progress and economy will depend on the circumstances, but economy should never trump smoothness, system or safety.

The line I take as an observer is that in an advanced driving context, economy should be seen as arising naturally as an outcome of good driving practices. It is not something to pursue too enthusiastically as an end in itself, otherwise it invariably compromises other aspects of the drive.

[trashbat]

How certain are you that this was a fair test? What proportion of this gain in economy might be down to other factors? I don't know.

Not particularly, but it was the usual set of drives, and resulted in something that bucked the trend of recent figures. I can and will repeat it. In fact this week I'm doing the opposite - the tank has injector cleaner in it, and I'm exercising that in lower gears than I'd normally use.

Looking at the general approach behind your experiment.... Personally I think it's illogical to buy a poky car then drive like a grandad to get a few more mpg. You'd be better off getting a more economical car and driving it normally.

I completely disagree with this. It's fine if you can have multiple cars to suit different purposes, but when you're stuck with one, it makes perfect sense that on the commute you might pursue economy whilst still wanting to go out for a progressive B road blast at the weekend. Add to that that we don't necessarily buy our cars based on either factor.

Otherwise, the rest of the post makes sense.

[WhoseGeneration]

For fun, at times, I'll do the "see how economical I can be", as shown on the dash readout, without compromising safety.
That's in a car with a readout, one without, well.
I would have expected that most here could easily drive and make progress, within NSL, with very respectable mpg for their particular vehicle.
It's called "acceleration sense" together with observation and planning.
However, that being said, as I commented in another thread, mpg bores are the new bhp bores.

[Mr Cholmondeley-Warner]

However, that being said, as I commented in another thread, mpg bores are the new bhp bores.

Which ones are more likely to be ski bores?

[7db]

I thought our just-more-than-half-a-dozen West Country posters were more likely to Severn Bores.

[TripleS]

I probably should have written 'always matters' rather than in the past tense. I only used it when I felt the situations warranted it; e.g. a straight 30mph road with no obstructions ahead. I think being able to perform unplanned acceleration to mitigate trouble is valuable in certain contexts, but I find it hard to identify where that'd apply in an urban 30.

I can't think of an example off the top of my head either. But the control a lower gear gives you isn't just the ability to accelerate. I don't have my copy of Roadcraft to hand to quote, but it talks about the accelerator being a control you can use to slow the car down as well as speed it up. As I descend through the rev range, I find that the ability to reduce speed with the accelerator drops off more than/earlier than the ability to increase speed with it.

I've always preferred to have high gearing and lowish engine speeds for most of my driving, and to use the highest usable gear, even in built-up areas. Having said that, more recently I have increased my usage of 3rd or 4th gear rather than 4th or 5th in 30 limits, largely on the basis that it more readily activates the over-run fuel cut-off, and thus aids fuel economy.

[Kimosabe]

I have found my fuel economy has worsened since starting on an AD course. I believe it's mostly to do with reaching cruising speeds faster than more gradually getting there. Over a 70 mile motorway journey, the half a mile or so needed to get to get to 70 means I'm pushing the 2ton car up through higher revs and gears which burns more fuel, than if I more slowly arrived at 70. The notion that remaining at 70 for half a mile longer saves fuel is negated by harsher acceleration and higher revs in each gear.

Thankfully, I have the option to engage a manual override on my auto box, which permits me greater sequential control of the 6 gears (alas no block changes). That adds to fuel economy. Otherwise, the ECU (remapped by Superchips) prefers to find the gear which favours cruising and the option to kick down if needed, over being at constantly optimum torque. This makes 'lifting off' and accelerator sense quite meaningless, as when pressure is removed from the accelerator, it will continue to cruise in that gear which feels as if its 'floating' in neutral, which then further requires manually shifting down and/or braking to rev/road speed match. Fuel economy watching spoils my drive! It can become quite a disjointed affair, when lifting off should equal greater deceleration. Fuel economy is a moot point in a brick-shaped, 2 ton, auto Freelander 2, with 19" rims.

Given the chance, I'd opt for a second car for pleasure and technical driving as well as my FL2.