ADUK Archive

You may have heard of Martin Lews (of moneysaving expert fame).

He's just published a blog post in which he extols the virtues of driving economically. In the following discussion there is much mention of different methods of driving economically, including one which made me think twice....

A quick counterpoint though: brake lights are a warning to cars behind, so using your brakes to illuminate the lights is useful even when you don't actually need to brake yourself. Also repeated engine braking can cause wear to the engine, so should be used moderately (as I'm sure you do) instead of as a replacement for brakes. My driving instructor said, "Which is cheaper to replace: brake pads & discs or a whole engine?"

He starts well, but what's that about engine wear under braking.....

Not sure why an engine would wear under engine braking. It's not like there's any friction material involved and if the wheels are driving the engine then there's minimal fuel being injected as well........

Chris

Cue someone to tell us gearboxes wear faster when they're being driven by the wheels...

Plenty of friction in engines, btw. That's why they're full of oil...

ScoobyChris wrote:if the wheels are driving the engine then there's minimal fuel being injected as well........

Chris

Generally none - overrun fuel cut-off.

Diesels and two-strokes rely on fuel for lube. Too much over-run with foot-off in those can cause excess wear, For those used to petrol cars it would be all too easy on over-run in a diesel to change down too soon and over-rev it.

Gearboxes are designed for high thrust when drive is from engine to wheels, but typically only medium thrust the other way (I'm sure off-roading stuff is the exception). Keep doing it both ways and it's like bending things to and fro (albeit not by much!). With helical cut gears, this is not only true of the gears meshing but also the shafts pushing end to end. Once play sets in there, sections (albeit minute) of gear previously unmeshed engage, and because of their subtlely higher spots take immense local strain which imparts through the surface and can lead to more rapid fatigue.

driving economically is always good BUT, IMO, it must not over-ride safety in any shape or form.

Mr Cholmondeley-Warner wrote:Plenty of friction in engines, btw. That's why they're full of oil...

I had made the assumption that the engine had the correct amount of oil in it, and so friction would not be a problem

Chris

Roger wrote:Diesels and two-strokes rely on fuel for lube. Too much over-run with foot-off in those can cause excess wear,

it's only the Fuel system on a diesel that relies on the fuel for lubrication, thats why theres oil in the engine, lifting the foot makes no difference to wear

Roger wrote:For those used to petrol cars it would be all too easy on over-run in a diesel to change down too soon and over-rev it.

this is true though, you just have to familarise yourself with the characteristics of the engine, but the same can also be said of a petrol 4-stroke

Using the engine to slow through acceleration sense, or even changing down in order to maintain a speed, for example going down a slope (but not to the extent that it is bouncing off the rev limiter!) if fine, but in my experience the problems come when drivers start to change down in order to slow down, effectivly replacing application of the brakes with gear changing. In my opinion there are few advantages to this, it is out of system, doesn't give any indication via a brake light, and as someone has pointed out, brakes are cheaper to replace than gearboxes.

fishter wrote:You may have heard of Martin Lews (of moneysaving expert fame).

He's just published a blog post in which he extols the virtues of driving economically. In the following discussion there is much mention of different methods of driving economically, including one which made me think twice....

A quick counterpoint though: brake lights are a warning to cars behind, so using your brakes to illuminate the lights is useful even when you don't actually need to brake yourself. Also repeated engine braking can cause wear to the engine, so should be used moderately (as I'm sure you do) instead of as a replacement for brakes. My driving instructor said, "Which is cheaper to replace: brake pads & discs or a whole engine?"

He starts well, but what's that about engine wear under braking.....

I think he's worrying unnecessarily there. A bit of extra engine braking is not going to cause any noticeable increase in engine wear rates, but a lot of downward gear changes and extra clutch activity will entail some increased wear in those areas, especially the clutch.

To be honest I'm not fully sold on the idea of 'brakes to slow, gears to go' as too much of a rigid rule. I think we need to try and be reasonable in our usage of various techniques, and I certainly use a moderate amount of downchanging, in conjunction with acceleration sense for general speed control purposes.

.... but then I still retain some old fashioned ideas.

Hey, you'll like this:

A week or two ago I had a good run home from a little spot a bit further down the coast. I decided to try and cover a decent stretch of road without use of brakes, but making good progress all the same. This was a road that includes some fairly fast sections, but it also has moderately steep hills, in some cases combined with tightish bends. The starting point was the first of two linked villages, and the finishing point was our arrival at a third village. The distance was 13.4 miles, and it included a maximum speed of about 95, and five overtakes. It was not slow, but it involved no braking whatsoever, and I don't think I used a gear lower than 4th. All a bit naughty, I know, but I felt quite pleased with that. Take care.

Edited to add that the one claim I will make is about being a decent economy driver, but that's all.

Best wishes all,
Dave.

Thought you might find this useful:
http://www.advanced-driving.co.uk/public/fuelecon.xls

TripleS wrote:[
To be honest I'm not fully sold on the idea of 'brakes to slow, gears to go' as too much of a rigid rule. I think we need to try and be reasonable in our usage of various techniques, and I certainly use a moderate amount of downchanging, in conjunction with acceleration sense for general speed control purposes.

.... but then I still retain some old fashioned ideas.

Hey, you'll like this:

A week or two ago I had a good run home from a little spot a bit further down the coast. I decided to try and cover a decent stretch of road without use of brakes, but making good progress all the same. This was a road that includes some fairly fast sections, but it also has moderately steep hills, in some cases combined with tightish bends. The starting point was the first of two linked villages, and the finishing point was our arrival at a third village. The distance was 13.4 miles, and it included a maximum speed of about 95, and five overtakes. It was not slow, but it involved no braking whatsoever, and I don't think I used a gear lower than 4th. All a bit naughty, I know, but I felt quite pleased with that. Take care.

Edited to add that the one claim I will make is about being a decent economy driver, but that's all.

Best wishes all,
Dave.

I know, the brakes to slow gears to go seems to be getting bandied about as more of an inflexible rule now, and things like half and 2/3's distance being forgotten about...............liked the "no brakes" exercise, have to admit doing that myself...........

Brakes for slow and gears for go makes tremendous sense in hybrids (Prious, Civic IMA, Lexus GS450) thanks to regenrative braking, provided the driver anticipates sufficiently well that the brake can be applied suffucuently lightly that friction dissipation is not called into significant play.

Roger wrote:Brakes for slow and gears for go makes tremendous sense in hybrids (Prious, Civic IMA, Lexus GS450) thanks to regenerative braking, provided the driver anticipates sufficiently well that the brake can be applied sufficiently lightly that friction dissipation is not called into significant play.

I've heard of regenerative braking systems on large heavy vehicles, but I didn't know it was on any cars.

How do you activate the regenerative braking system only, without bringing the normal braking system into play? Is there a separate control (i.e. other than the brake pedal) to operate the RBS ?

Best wishes all,
Dave.

our LGV's have a retarder on the gearbox (automatics) which is actuated by the driver coming off the throttle, it also switches the brake lights