Pulse and Glide driving technique - the forum says NO! ;)

darich

Tojo_Ralph wrote: »

In the interests of research, I tried the 65 to 60 and back again today and I am now even more convinced that it is dangerous and I now realise just how bl00dy difficult it is!!

So driving along at 65 on the flat, I lift my foot off the accelerator and it takes just 7 seconds for the speedo to fall to 60 mph .... So it's back on the accelerator and easing the car back to 65 mph takes 8 seconds .... Then it's foot off the accelerator for 7 seconds .... On for 8 seconds .... off for 7 seconds, etc, etc, etc .... And all the time I am spending more time monitoring the speedo than I am spending watching where I am going.

And above all else, it's hard work monitoring your speed to the point of fluctuating up and down between 60 mph and 65 mph TWO HUNDRED AND FORTY times an hour!!!

Sorry..... Give me cruise control any day.

So in your case, for every minute of driving, you're accelarating for 32seconds using more fuel and for only 28secs, slowing down using less.
That would probably indicate that the technique, on your figures, uses MORE fuel since more time is spent accelerating.

And i completely agree about checking the speedo every few seconds is a danger.

I'm more than happy to use my cruise control all day and even in my 3.0 sports car i can average around 40mpg on a long run holding a constant 60-65mph.

darich

tomstickland wrote: »

Smallest engines are not always the most economical at motorway speeds. And there's very little correlation between engine size and car sale price on second hard cars.

Your second paragraph agrees with the statement though - the difference is so small that it takes ages for the lorry to overtake.

I agree with you and that smaller engines aren't always more economical. From personal experience and on motorway driving, i reckon the most economical size is around 1.4-1.6. Any smaller and it's a constant effort to maintain a reasonable speed. Any larger and the fuel usage increases past the point of economy.

I can see what you mean about my second paragraph but the point i was making was that the tiny difference is noticeable and annoying to other drivers. To the driver in the car it may not be noticeable, but it is very noticeable to those wishing to pass but held up for several hundred metres.

tomstickland

So in your case, for every minute of driving, you're accelarating for 32seconds using more fuel and for only 28secs, slowing down using less.
That would probably indicate that the technique, on your figures, uses MORE fuel since more time is spent accelerating.

Not if they use virtually nothing for 28s versus 1.8 times as much as per steady speed for the 32s.

darich

tomstickland wrote: »

Not if they use virtually nothing for 28s versus 1.8 times as much as per steady speed for the 32s.

True,
I'm sure this technique probably works when used on level, good condition roads. But when travelling over bumps, potholes (yes even on the motorway) and going up hills then i'm fairly sure the technique is, at best, no better than driving at a constant speed.

shown73

Having just driven round the northern half of the M25, and back again, today, this whole discussion seems irrelevant really. The "Pulse" tecnique was zoom along, stop, zoom along, stop. The question of ultimate fuel consumption quickly became subservient to an overwhelming desire just to get to the destination before the onset of terminal hunger/thirst, or desire to have a wee! Or worse....

steve6375

Pulse and Glide - interesting result!

Hi
As explained in a previous post, my 2.2SRi Vectra Estate Auto does 26mpg with normal country road driving and using only light acceleration.
P&G gets me to 30mpg.

Recently, I went on a 20 mile journey to help my brother move house. On the way there I got my usual 30mpg even with one passenger. Before I left to return home, my car was filled with loads of heavy junk to take back and the passenger.
I expected the mpg to be worse, but to my suprise it was better at 33mpg!

I can only assume that the car being heavier made the inertia affect greater so taking my foot off the accelerator to 'glide' did not slow the car down quite as much as usual - whilst accelerating back up to speed did not use that much more fuel. So in future I am going to fill up my petrol tank rather than just half-fill it to see if this gives me better mpg!

On another note, my friend tried the P&G technique and he said his manual gearbox car really slowed down quite a lot whereas my automatic does not slow down as much as his car did when I gave him a lift and demonstrated the technique to him. So P&G may be more useful for autos than manual cars (unless you drive in neutral or use the clutch to glide which of course cannot be recommended).

All I can say is that in my car (auto) I can get 26mpg driving 'carefully' but 30mpg using P&G. I have repeated this many times going to work and back every day and it is effective. I doubt if any car behind notices what I am doing as I don't yo-yo between 60mph and 40mph but rather between 55mph and 45mph if the car in front is doing a constant 50mph. This creates a nice gap in front of me for a short while which I shorten when I accelerate mildly back up to 55mph before taking my foot off again. With an Auto transmission the engine braking affect is not very severe.

mark55man

Steve

Your post matches my experience exactly. With a 100yd gap between cars the variation as I go between +/-5mph over the rolling average hasn't caused any flashing or reactions at all. definitely more efficient

the only time I felt nervous doing it was on a dual carriageway where a car overtaking me thought I was trying to race him up the inside, but I braked a little and he was off and happy.

Thanks

steve6375

So, to summarise, in this topic we have 4 people who actually tried this technique and all the others just scoffed at it.
Of those 4 that actually tried it, 3 say it definitely improves mpg. The other one only tried it between 60 and 65mph. This will not be as effective as 60-70mph and it will be even more effective at 40-50mph as engine braking is less severe at lower speeds and at 40mph the car will pretty much stay at that speed in top gear with no pressure on the accelerator.

All I can say is try it. DON'T look at the speedo, just try to take your foot off the pedal for as long a stretch as you can whenever you can.
It is a simple technique that can save you ££££s and you get there just as quick and no one behind really notices. If the road is busy you cannot do it though, so it depends on your route.

Don't scoff until you try it, then post your results here. It would be interesting to know if it works better for autos rather than manuals.

redux

steve6375 wrote: »

So, to summarise, in this topic we have 4 people who actually tried this technique and all the others just scoffed at it.

The technique was developed by fans of hybrid cars such as the Prius, and in the most extreme cases involve driving at a speed which fluctuates between 20 and 41 mph. Definitely not above 42 mph as that is when the engine will restart.

I'm not going to do that on the motorway.

With other cars that are designed to have the engine off for part of the time, such as the VW Lupo and Audi A2 1.2 TDI 3l, versions not sold in this country, then it could be useful.

In an ordinary car, coasting in neutral with the engine running still uses fuel. Stopping the engine may stop the mileage being recorded, which renders any consumption calculations invalid. And it isn't necessarily safe or legal.

So for ordinary cars, I'll remain sceptical. I don't think merely keeping your foot gentler on the pedal, or following lorries uphill and only overtaking them downhill, counts as pulse and glide; there isn't any glide. Yes you can save something by varying between 60 and 70, but probably the same as travelling at 65 anyway, especially if before the fuel saving efforts it was perhaps actually 75 mph.

steve6375

So have you actually tried it? I have and I use it every day.

How can you hypothesise that it does not work when you have no experimental evidence to back this up or personal experience and when 3 other people have actually tried it and they do say that it works?
How can you just ignore the evidence?
The technique of P&G is not a 'gentler on the pedal' technique (which is 'granny driving') but taking your foot OFF the pedal completely (which gives you 150mpg rather than 30mpg).

Please try it and post your results and type of car you have. If you think it does not work then prove it - don't just hypothesise or read theoretical guff on the internet - what is the point of that!

Whatever the reason, it does seem to work on at least some cars (proven in 3 cases on this forum), so what have you got to lose by trying it?