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

pault123

Disproven by MSE, pulse and glide is strictly for the Hybrid cars. Although its an interesting theory none the less.


Pulse & Glide or P&G for short originally started in the Prius hybrid cars which automatically shut the transmission off when going below 40mph with your foot off the revs but can be emulated to a good effect on all cars.

It can be done by going up to say 70mph (or whatever speed is appropriate for given road) and then "gliding" down to 60mph by simply taking your foot off the revs and letting the car roll in the highest gear possible for that speed, (OR putting into neutral for a longer glide although of course this is illegal )

.... then revving (or pulsing) up to 70 again. Watch the mpg rocket up while gliding. The glides work very well on slight downhill gradients.

Any speed combo works 50mph-45mph, 30mph-25mph etc.

The "neutral gear" VS "highest gear with no revs" argument is based on the engine using a *slight* amount of fuel to tick over in neutral but with a longer distance covered, VS higher gear with no revs where the engine completely cuts off all fuel to the engine but you don't cover as much distance due to engine braking.


See here for the extreme engine off version which I do not recommend. >>>

http://www.metrompg.com/posts/pulse-and-glide.htm


Theres a very interesting forum where people with TDI engines aim to join different mileage clubs out of one tank! There is a 1000, 900, 800 and 700 miles club on one fuel tank!!

anewman

pault123 wrote: »

...by simply taking your foot off the revs and letting the car roll in the highest gear possible for that speed, (OR putting into neutral for a longer glide although of course this is illegal )

Not illegal in itself, but it can contribute to losing control, and if it led to poor driving you would be putting yourself open to charges of driving without due care and attention or something.

Besides, coasting in neutral in most modern cars INCREASES fuel consumption, as the engine has to idle to keep going - whereas with most modern engines having your foot off the accelerator, and being in gear, means the momentum of the car keeps the engine running without the need for fuel. So DO NOT COAST as it does not help fuel efficiency and has the potential to be dangerous.

Accelerating in itself uses lots of fuel, so there's no point in accelerating to 70, then slowing down, only to accelerate again. Driving smoothly at a constant speed is probably better for fuel efficiency - and speeding up and slowing down repeatedly probably wouldn't impress other road users.

As for going down hill, your engine needs less effort then anyway so MPG increases for all cars - but unfortunately although Britain's economy is all down hill, the roads aren't.

vaio

pault123 wrote: »

Pulse & Glide or P&G for short originally started in the Prius hybrid cars which automatically shut the transmission off when going below 40mph with your foot off the revs but can be emulated to a good effect on all cars.

It can be done by going up to say 70mph (or whatever speed is appropriate for given road) and then "gliding" down to 60mph by simply taking your foot off the revs and letting the car roll in the highest gear possible for that speed, (OR putting into neutral for a longer glide although of course this is illegal )

.... then revving (or pulsing) up to 70 again. Watch the mpg rocket up while gliding. The glides work very well on slight downhill gradients.

Any speed combo works 50mph-45mph, 30mph-25mph etc.

The "neutral gear" VS "highest gear with no revs" argument is based on the engine using a *slight* amount of fuel to tick over in neutral but with a longer distance covered, VS higher gear with no revs where the engine completely cuts off all fuel to the engine but you don't cover as much distance due to engine braking.


See here for the extreme engine off version which I do not recommend. >>>

http://www.metrompg.com/posts/pulse-and-glide.htm


Theres a very interesting forum where people with TDI engines aim to join different mileage clubs out of one tank! There is a 1000, 900, 800 and 700 miles club on one fuel tank!!

Sounds like it would increase the amount of fuel used rather than decreasing it. (at least if my understanding of the laws of physics is right)

mark55man

The thing about laws of physics there are so many of them, but all of them rely on verification by experiment. What the OP is stating is that despite what posters #2 and #3 say is that pulse and glide is more efficient as demonstrated in well controlled experiments.

Having read the threads referenced pulse and glide works because use of the engine at a steady pace incurs more friction than doing pulse and glide which uses (in its extreme form - engine off) no fuel during the glide (and incurs only minor friction at 1000rpm or so when coasting, or with some modern cars when the engine management cuts of fuel when in gear but no accelerating).

That is in steady you incur a constant fuel burn including a steady friction cost, in P&G you incur a greater friction for a small portion of the time, and a much less friction for the rest of the time.

I think I will try it next week on my way to work (try it = on an empty road and with engine management to look after the glide not coasting or engine off). My car is Vauxhall Zafira 1.8 petrol I currently average 39mpg on a mixed urban/rural route

Thanks OP - should save me even more money on my driving. I am now spending less than 6 months ago beause of being more careful

tomstickland

I can just about believe that this might work.

If the car is driven at a constant spead with light throttle angle then it will be efficient, but the engine will not be operating at the most efficient loading.

With the advocated method, the engine could be run for a short period at near optimum lead (approx 50% throttle) and then ideally tuned off and the car allowed to roll. The next option, leaving it in gear and no throttle, will as explained, use less fuel, but will slow the car more quickly.

Shimrod

It's also a very good way of annoying other motorists, especially if you get stuck behind someone doing this on a single carriageway road.

tinkerbell84

I just hope I'm never unfortunate enough to be driving behind you (or anyone else doing this).

Maybe you should get a bumper sticker that warns people that you'll be driving erratically :rolleyes:

Tojo_Ralph

.....
I have no problem with people having the good sense to drive their vehicles economically, but a motorist who is hell bent on saving every last drop of fuel and who is continually monitoring his speedo as he increases and decreases his speed between 60 and 70 mph is in my opinion a danger to both himself and all other road users.

Hopefully the Police would also take a dim view of such a driving style and act accordingly.

vwjo

I can verify what pault123 is saying - I have already noticed this myself.... personally though, I think some respondents are taking the suggestion a little too literally - for me it really is quite a slight change of speed, certainly not anywhere near enough to either annoy a fellow motorist, or to distract me from driving. Simply a very subtle lessening of keeping the foot set in one position.

Tojo_Ralph

vwjo wrote: »

I can verify what pault123 is saying - I have already noticed this myself.... personally though, I think some respondents are taking the suggestion a little too literally - for me it really is quite a slight change of speed, certainly not anywhere near enough to either annoy a fellow motorist, or to distract me from driving. Simply a very subtle lessening of keeping the foot set in one position.

So what would the slight change of speed be on say a motorway?

The reason I ask is that I don't see how a car that fails to maintain a constant speed when road conditions allow can be anything other than a nuisance.

If we assume a small fluctuation in speed between 65 mph and 60 mph, that means the car travelling at 60mph travels 440 ft less in a 60 second period than the one travelling at 65mph.

tinkerbell84

And lifting your foot off the throttle won't show people behind you that you're slowing down, so expect someone to hit you at some point (sadly that will most likely go down as their fault).

Seriously hoping this doesn't become a driving trend - it's bonkers!!!