Freewheeling to save money

Ultrasonic

EdGasket wrote: »

Re. the previous post; I don't see why slowing down earlier is 'not practical with other traffic around'; seems very safe and sensible? If other drivers want to drive as fast as possible and slam on the brakes at the last minute then that's their problem not mine. I am happy to approach junctions and roundabouts gently decreasing speed and yes, coasting where appropriate.

It is a question of curtosy to other motorists and to some extent safety. I could get some really quite exciting economy figures if I drove with complete disregard for other drivers and always slowed down in neutral from a long way back such that I never have to touch the brake. If I actually did this I'd spend much of the time with angry drivers behind me. Going slower than other drivers expect further away from junctions also increases the risk of other drivers ending up dangerously close to the back your car. Of course you can argue that this shouldn't happen, but it will.

Merely slowing down in gear results in starting to decelerate earlier than most drivers do, and I therefore won't always do this as early as would be optimal for fuel economy for this reason. Decelerating in neutral you can start decelerating MUCH further back than other drivers expect.

Bongles

Ultrasonic wrote: »

On my drive home I have a long straight road with a 60 mph limit leading up to a large roundabout, which I would ideally want to reach at about 25 mph in 3rd gear (it's open so you can see if other cars are approaching the roundabout from other directions). If there are no cars behind me then I can stick the car in neutral and slow down over a much longer distance than I would under more normal traffic conditions with cars behind where I would start to slow down later in gear, and decelarate more rapidly. The fact that the road is straight means I can see if there are no cars for a considerable distance behind me.

Yes, for coasting in neutral you want to be starting to slow down much earlier to arrive at the junction at the same speed as you otherwise would. This is not practical with other traffic around but can be when roads are quiet.

I do understand your point - you'll see in the thread Chickabiddybex started that I explained it to someone else who I think had misunderstood you - and I can visualise your example, at least hypothetically. It's just that I can't bring to mind a situation where I would want to start slowing from, say 60 to 25, early enough to achieve all my deceleration though engine braking alone, let alone even earlier than that.

I'd have to drive around a bit looking for examples and doing some experiments. First step I think would be to measure how far my car travels after lifting off at 60 and staying in gear and how much time it takes to slow. Of course it would travel further doing that in neutral, but even in gear I'm sure it would go a lot further than the distance I would normally brake over before it was down to, say, 25.

Ultrasonic

Bongles wrote: »

I'd have to drive around a bit looking for examples and doing some experiments.

That would rather defeat the object of trying to save fuel .

First step I think would be to measure how far my car travels after lifting off at 60 and staying in gear and how much time it takes to slow. Of course it would travel further doing that in neutral, but even in gear I'm sure it would go a lot further than the distance I would normally brake over before it was down to, say, 25.

Measuring how far, or how long, it takes to decelerate wouldn't really be of much use. You want to be making mpg comparisons for the different techniques. But if you aren't comfortable slowing down in gear over longer distances I'd definitely do that first, where appropriate.

Bongles

Ultrasonic wrote: »

That would rather defeat the object of trying to save fuel .

That's OK. At the moment my interest in this isn't about saving fuel. While I see how this works hypothetically, I'm still at the stage of being skeptical but intrigued about whether it can be applied in the real world. I know you're persuaded, but I'm not yet .

Ultrasonic wrote: »

Measuring how far, or how long, it takes to decelerate wouldn't really be of much use.

I need to know in order to search for a real world hazard for which this would work. Once I know that my car will engine brake from, say, 60 to 25 in x-hundred metres, I will know to eliminate from my search any hazard for which I am not prepared to start slowing from further than x-hundred metres away. I have a sneaking suspicion that that will eliminate just about every hazard there is, but I might be wrong.

In fact I've just had a go at the experiment. I was doing 57 at the start when I lifted. About 400 metres later, when I stopped the experiment because I had to brake for other traffic, I was still doing over 30. That's engine braking in gear (top gear, obviously). So I know now that to put your theory into practice, I am looking for a situation where I am happy to start slowing from considerably more than 400 metres away.

goonarmy

Gloomendoom wrote: »

Not in the case of Land Rovers because only the front wheels freewheel when running in 4x2 mode, the rears remain firmly connected to the engine unless the gears are knocked into neutral or the clutch is dipped.

That only applies to series vehicles from the early eighties at the newest. Lr were all 4wd upto the poitn when the freelander/evoque started being 2wd. And the front axle with a diff assembly is not really freewheeling. You can get overdrive but that reduces rpm rather than freewheelling.

Gloomendoom

goonarmy wrote: »

That only applies to series vehicles from the early eighties at the newest. Lr were all 4wd upto the poitn when the freelander/evoque started being 2wd. And the front axle with a diff assembly is not really freewheeling. You can get overdrive but that reduces rpm rather than freewheelling.

:huh: That was the point I was making. With exception of front hub freewheels, Land Rovers, or any Rovers, have not had a device fitted that allowed the transmission to freewheel since the 1950s.

BTW some 'Series' Land Rovers were made with 4x2 only.
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ikolpdog_2

Glad I read this, I can now cancel that order for a 2013 Volkswagen CC with its DSG gearbox and inbuilt coasting function....TO IMPROVE ECONOMY.

So many experts here who know so much more than Volkswagen, they really aught to employ some of you!

goonarmy

ikolpdog wrote: »

Glad I read this, I can now cancel that order for a 2013 Volkswagen CC with its DSG gearbox and inbuilt coasting function....TO IMPROVE ECONOMY.

So many experts here who know so much more than Volkswagen, they really aught to employ some of you!

They do.;)

Ultrasonic

Bongles wrote: »

That's OK. At the moment my interest in this isn't about saving fuel...

If your interest is more academic you might be interested in getting some sort of OBDII monitor. I have a ScangaugeII but there are others available. The Scangauge has a 'Performance monitor' feature which will allow you to log data over test runs. (I got mine primarily for the load indication and have never got round to trying the Performance monitor out.)

Edit: you might also find the following thread from Ecomodder (and much of the rest of the forum) of interest:

http://ecomodder.com/forum/showthread.php/coast-neutral-vs-gear-ive-been-challenged-show-22841.html

almillar

A few things for me to catch up on...

Coasting then, is for when you no longer need the throttle, but don't want to slow down as much as you would with engine braking.
Is there a real life example you can give to illustrate when you might do this - slowing down off brake, off throttle and out of gear (or clutch down at least)?

> Perhaps coming up to a queue of traffic / traffic lights (on red) that you can see in the distance with nobody behind you?
> Slowing down for a speed limit, which has a roundabout or traffic lights (on red) within throwing distance of the sign?

Thanks anotheruser!

I've added the bold to the last bit there because it's important. As I understood it, he was talking about coasting achieving all the required deceleration.

Maybe all the way to 0 MPH, maybe not. You can NOT use engine braking all the way down to 0 though, as you'll stall, so you have to coast for at least the very last bit if you're stopping!

Do NOT coast in the snow or ice!! This is the time you DO need to be in full control of your vehicle and not thinking about MPG!

Retrogamer - try reading my original post to show how coasting CAN be more efficient than engine braking.
As far as I understand it, diesels have always had a type of injection system (electronic or otherwise) that doesn't use fuel on the overrun, so the same rules apply.

Weird Nev - post 61 - I'm talking specifically about saving fuel safely. And not at the expense of other road users either. Show me any examples of mine that you think are unsafe or unprogressive. I'll be driving at the speed limit if possible!

ikopdog - you can cancel your order now anyway since you've learnt how and when to coast safely! ;-)