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

redux

steve6375 wrote: »

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!

Sorry, but I'm not going to undertake to drive an 800 or 1000 miles tankful oscillating between 40 and 60 mph, so there's no way to compare the fuel consumption.

A couple of years ago I averaged 85 mph and 47 mpg on 660 miles across Austria and Germany. Even though I was doing 80-90 uphill and 95-115 downhill where legal and possible, and the faster downhill used less power, I don't count that as pulse and glide. If I'd slowed down I'd have spent money on a hotel bill instead of getting home at 1.15 am, then paid more for the Channel crossing and got to work after lunch instead of before 10 am. What advantage would this technique have brought to that trip?

Most estates are less economical than the saloon equivalent, by the way, and that isn't just hypothesizing or theoretical guff on the internet. But even so my old 1966 Volvo 221 Amazon estate managed to average 29 overall, or 36 mpg on a long run at 65 to 70 mph. Perhaps your modern Vauxhall needs servicing or tuning a bit if it uses more fuel while still 15 mph slower, or perhaps you might get swap it for one with manual transmission or a different type with a more efficient automatic gearbox, such as those from VW Audi or Citroen and Peugeot. I remember someone 22 years ago who said his X-reg (suffix) Cavalier saloon did 33 to 36 mpg, and fuel injection should have improved things over carburettors then.

Or is it your driving style?

When you've switched to diesel and can beat 60 mpg in a car that size, then come back and patronise me again.

pault123

Interesting to see some people have had positive results with it. I do agree the gliding in gear is a lot easier in lower gears such as 3rd or 4th, the distance which can be covered without any significant loss in speed is superb.


"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."

I think that explains how little it should be thought about, it doesn't have to be as "clinical" as the P+G guides suggest

AdrianHi

I had a bit of an experiment with pulse and glide on the way to work this morning.
OK I guess it might save a bit on fuel, I got marginally, as in 0.7mpg out of 48mpg better, on the OBC mpg display for the trip. This could be down to other factors such as which way the wind is blowing today.

I did it for half an hour.
I found it to be a very tiresome and distracting way to drive. Paying too much attention to the speedo to make sure I was not dropping to too slow a speed for the gear, because coasting I don't have the engine sound to give me a queue.

Good luck to those who want to do this, but I'm dismissing it as a dangerous and unpleasant way to drive. No offence meant to anyone, it's just an honest open expression of the way I feel about driving like this.

steve6375

Hi Adrian
Thanks for trying it and posting back. Scientific results are always preferable to theory!
If you have an onboard computer as you have it is very easy to test it out - you don't need to use a full tank full!
Your results are not really conclusive.
I think the main thing to remember is that whenever you lift your foot off the accelerator slightly, ask yourself the question 'can I lift my foot off completely?'. Whenever you lift your foot off completely remember you are travellling at over 100mpg, if you use just 1/4 throttle to maintain your current speed, you are using say 35mpg.
When you approach a junction, take your foot right off - why keep your foot on and then brake at the junction when you can take your foot off and travel that last 100-200yds for free?
When travelling downhill, take you foot right off - if you slow down too much then accelerate again and then take your foot right off again.
Just use the technique whenever you feel comfortable with it - it will give you results, especially on lower speed roads.

AdrianHi

steve6375 wrote: »

Your results are not really conclusive.

Agreed, to be really scientific about it you would need a more controlled test.
I also have an instantaneous mpg meter on the car which is a fairly coarse measurement but shows zero (100mpg+) fuel when foot is off accelerator but you are in gear. When coasting completely it shows fuel used in the 60-100mpg range depending on speed.
I understand it's a balancing act between the effect of engine breaking vs. coasting further. I think in the end any saving you might get doing this is going to be so small it's not worth the bother, unless perhaps your in a Hybrid.

There are a few other things I have done which together has gained me an extra circa 4mpg on this same trip.

michaels

You'd never guess that as a country we can't do science.

I do pulse and glide on the m25, indicated 80 on each speed camera up to about 95 between them - it uses much more petrol and !!!!es people off but does save money (no speeding tickets) and probably saves about 30s every day and I do value my time

pyuicd

I have tried pulse and glide myself and had good results. Although it seems counter intuitive, I believe it works because the engine operates more efficiently when accelerating harder than just maintaining speed, i.e. more power produced for the level of fuel consumed. Therefore if this is balanced with a glide you have made an MPG gain.

Just got 67mpg on a 15 minute trip using P&G compared to 55 mpg for the same journey normally (BMW 320d, trip computer). I only do it on empty roads or when I do night driving and no one is about. The gut response of some folk here is pretty rude and uninformed, i'm no environment nut and I've done this just occasionally (maybe 7 times ever). Most times I value my time more and will drive much faster or with CC. It isn't something to be done every journey but in the right circumstances, why not? As has been said you don't do it like clockwork, and if you tried it and found it dangerous then you did it at an inappropriate time or place, or simply need more driving lessons. Don't coast in neutral, stay in gear. It works well and is better driving.

feelingthepinch

I drive an 03 plate golf TDI with an in-dash trip computer that measures realtime and trip-average fuel economy and I've had great results with P&G (with glide in gear).

I often have cause to do a 80+ mile run up and down the motorway to visit friends and family.

Conventional driving at just over 60mph has returned for me at best 61.1mpg average door-to-door, usually around 58mpg.

P&G going from 60mph to 65mph for the same journey has returned at best 67.7mpg average door-to-door, and always over 65.0mpg average.

I've also noticed that the fuller (i.e.: heavier) my car, the better the result.

So i'm looking at roughly a 10% improvement in fuel economy on my best result for P&G over my best result for conventional driving.

Arfa__

I used this technique a few times with positive results. I have a Vauxhall Zafira 1.6 on LPG. I have a Scangauge II diagnostics thingy plugged into the cars ODB2 socket, which give me an accurate running average MPG and current MPG.

I only use this technique on the motorway when not too busy. On a long run (100+ miles) you really notice the difference. Normally holding the car at a constant 70mph (3500revs) a trip to parents (M25/M1/M6/M54) I can expect to achieve 28-30mpg average. However with P&G, I will slowly edge this up quite significantly over the journey: 35+ MPG is easily achievable. This will be pulsing between 65-75mph ish. Drop the speed down a spot and P&G between 60-70mph and I can hit 38-39MPG ish.

As I pulse, foot to floor, my MPG will drop to about 10 ish. Foot off and I get a reading of 9999MPG i.e. infinite, no fuel being used. Ultimately I will be accelerating for far less time than I'm gliding. Not timed it exactly though.

Note: I wouldn't do this on a busy motorway, with lots of clumping, through variable speed limit sections, residential areas etc.

Now for those having trouble glancing at your speedos, what do you do on the variable speed limit sections, where there's a new speed limit on each gantry?!

Mark_Hewitt

I have noticed this does indeed work. My average MPG tends only to increase when my foot is off the accelerator, so the more time I can spend using no fuel the better MPG I get.

On the motorway going between 60-65 is a bit too quick, better results are obtained just following a lorry at a safe distance. However on twisty country roads where speed varies natually anyway it works well, mostly by using the throttle on downhill sections and then lifting off around corners and hills if possible.