http://www.popularmechanics.com/cars/alternative-fuel/news/coasting-in-neutral-fuel-economy

are your brakes dragging- in top gear i find it to have little effect on how far my car goes – while remaining safely in control of my vehicle should i need to make a sudden adjustment to my speed or my direction.

oh and wether i go at 65-70 or 82 on the french peage i return between 39-42mpg in my non turboed diesel.

trail_rat – Member
http://www.popularmechanics.com/cars/alternative-fuel/news/coasting-in-neutral-fuel-economy

are your brakes dragging- in top gear i find it to have little effect on how far my car goes – while remaining safely in control of my vehicle should i need to make a sudden adjustment to my speed or my direction.

oh and wether i go at 65-70 or 82 on the french peage i return between 39-42mpg in my non turboed diesel.

TR – that’s a perfect example of why you shouldn’t believe everything you read on the internet. Read the comments below and you’ll begin to understand that the guy is compare apples and pears. He’s talking about coasting to a stop in gear off throttle vs out of gear at idle and that’s a no brainer. What we’re all talking about it knocking it out of gear downhill and coasting as far as you can within reasonable speed limits.

Re the control thing the only thing I’m missing is the ability to speed up and if I need to do that significantly I’ll have to change down from 6th anyway so it’s reaction time neutral. The brakes and steering still work as they would normally so safety is in no way compromised.

so provide some evidence to the contrary then ? other than your opinion. that is not my basis for my opinion – it was just the first hit on google.

The “199mpg” reading is your ecu shutting the injectors off. It’s all added to the average.

It takes about 720w to cold crank an average engine at 1500rpm (12v X 60a). An average family car’s brakes are capable of producing about 350kw (yes, about 500hp). Engine braking is pretty pointless.

hot_fiat, your value for brake power must be a max value? You probably brake normally with 10% of that or even less?

What does ‘engine braking is pointless’ mean? In 6th gear, yeah maybe. But change from 6th to 4th in my car at 70 and take your foot of the throttle and you really notice the engine braking.
Find a steep hill and drive down it with your foot on the clutch. Now do it again with the car in 3rd gear….any difference?

Given the frequency I have to check the speedo in this radared age the instant fuel consumption has become my favourite option for the other readout. It tells me fascinating things like the optimum gear for crawling along at the speed limit. Third for 30kmh limits, Fourth for 50kmh limits and fifth above 60kmh. 75-85kmh in fifth is the speed that returns the lowest fuel consumption with a steady increase thereafter (so fifty really is thrifty). Up mountain passes a light throttle opening with the engine spinning at peak torque yields the best results.

Winter tyres really do use more fuel that economy tyres at the same speed on the same road. It’s worth changing down rather than rolling up to junctions in a high gear as it cuts off the fuel. Using a route nationale uses less fuel than the autoroute even if the nationale goes through towns. 5.7l/100km on petrol over the last year according to the average economy readout.

On the downside it’s just another distraction.

Coasting in gear.. hmm.. it uses no fuel, but it slows you down a little quickly sometimes. I reckon when you are approaching a roundabout or something you can lift off and give it just a tiny bit of pedal (rather than none), you slow down very very slowly but your mpg goes through the roof the whole time. Of course not suitable for busy traffic where being ‘normal’ and flowing with everyone else takes precedent.

I do drive for fuel economy, of course – but without being an idiot about it. I put my cruise on 70 on the motorway and relax. On windy roads I concentrate on being as smooth as possible, keeping my momentum as much as I can and putting in bursts of throttle at the right times, coasting at others. I also use cruise whenever possible in 40s and 30s to keep speed consistent. I’ve noticed that if you ease down on the pedal so gently that you don’t notice any acceleration, the mpg still goes through the floor, so cruise limits these constant variations.

I got 62mpg from Cardiff to Farnborough the other day, in my auto pre-bluemotion Passat.

Incidentally, before I got the Prius I’d drive at 80 everywhere and not hang around on normal roads. Only when I got the graphical readout on the Prius did I see how much effect it had on my averages, and because I bought the car for economy (why else) I started trying to keep it up as much as possible. I do wonder what my Seat would have done had I driven it knowing what I now know.

Winter tyres really do use more fuel that economy tyres at the same speed on the same road.

Depends on the tyres – Nokian WR G2 were a huge improvement in MPG over the Dunlop Sports – about 10%.

Given up worrying about it – however I drive (mostly dual carriageway) it only makes about 1.5p per mile difference.

30mpg average on a tankful is but a dream to me.

Incidentally, I got 62mpg coming down to Surrey the other day; I did 82mph on the way home and got 54mpg.

I did a little experiment a while back. Spent an entire two weeks driving as gently as possible. Real granny stuff. Coasting every hill in neutral, as far as I possibly could. It was difficult. The urge to hit the accelerator, just squeeze it a bit and start moving a bit faster was strong. And once I’d rinsed a tank of petrol, I discovered it hadn’t really made any difference at all.

Don’t have a fancy pants computer, so not a massively accurate experiment (I know how much I get to tank…), but it seems either:

a). I don’t have a car that responds well to economical driving.
b). It’s all bo**ocks.
c). I’m a very economical driver already.

I discovered it hadn’t really made any difference at all

You did it wrong then. Driving economically isn’t necessarily about driving slowly. Accelerating slowly for example is worse than accelerating moderately and holding speed.

Lowering your cruising speed does make a big difference on motorways though.

butcher – Member
And once I’d rinsed a tank of petrol, I discovered it hadn’t really made any difference at all.

Where as in mine (2.0 DCi) it can make up to 100m difference over a tank of fuel driving conservatively vs normally.

conservatively means:-
70-74 indicated on cruise control on motorways (depends on traffic conditions and how much of a hurry I am in)
60mph on A roads
40-42 indicated in a 40
30-32 indicated in a 30
driving to conditions everywhere else
Coast out of gear down as many hills as possible and aim to be back in gear on throttle before I get bored or something catches me up
Use as light a throttle as possible to maintain those speeds and as few revs as I can get away with (helps it’s a torquey 2 litre turbo diesel)
That’s not to say I don’t make progress or overtake when the opportunity arises. I dare say I could get another 5mpg consistently if I were more patient.

Oh and Aircon – I haven’t done a major comparison between on or off as I don’t do any regular journeys to measure it on but it certainly feels like it’s a big drain.

I never turn my A/C off, I let it manage itself. If there’s any difference (on either car) between A/C on and off, it’s lost in the variation of different journey types.

I don’t do the same trip all the time though so I don’t have good reliable data to compare small changes.

molgrips – Member
I never turn my A/C off, I let it manage itself. If there’s any difference (on either car) between A/C on and off, it’s lost in the variation of different journey types.

I’ve tried a week here and there with my climate control set to econ which basically turns the air-con bit off and there is no appreciable difference. Like you say, I suspect any improvement is lost in the week to week variation from things like traffic, short trips into town etc.

I think on smaller engines it makes a difference. My Wife’s Ka had aircon and it was noticeably more sluggish with it on. But that was a 1.3 8v with about 60hp.

Depends on the tech I think. I went out with a girl who had a Hyundai Accent, about 2000 or so. It was American spec so had a pokey de-tuned 1.6l engine with a crap old fashioned auto box and presumably a massive old-tech A/C compressor. In all the older cars I’ve read Haynes manuals for there’s a switch to disable the AC when you floor it, but this didn’t have it. If you were attempting to accelerate to motorway speeds, you could hit the A/C button and feel a proper kick of acceleration.

Most A/C clutches are disengaged by the ecu upon peak throttle demand. In the abarth you can hear the high pressure side re-pressurising following bouts of heavy footedness.

@stumpy – you’d be surprised how hard brakes actually work. Yes 500hp is peak. Though I wouldn’t have thought 80-100hp was an unreasonable braking power for normal deceleration, even around town. (you decelerate a damned site quicker than most cars accelerate).

Peak power from engine braking really does max out at a couple of KW. Its fine for holding your speed down a hill, if you’re a mentalist & like to unsettle a car before a corner, or if you think that’s how racing drivers drive (they don’t*); but for actual slowing down brakes win.

*in fact one of the many unsung technologies that’s come out of racing is MSR which actively works with the electronic throttle to reduce the effects of botched downshifts engine braking to ensure smooth transition into the bend. In a passenger car this is used to assist ABS in preventing wheel lock-up. In reality it’s all the same system doing the thinking, just Bosch like acronyms.

Yeah, doing a quick fag packet calculation, braking power is quite high!

I get a car (1500kg) braking from 70mph to zero in 15secs needs the brakes to work at a constant rate of 48kW, which is about 64hp.
And I suspect most people coming off a motorway to a roundabout or junction don’t give themselves 15s to stop.

(Using: KE at 70/time taken to stop to get the power required and then dividing that by 745W (1hp).)
A lot of assumptions in there – it wouldn’t be linear for a start.

Always an interesting one. I drive a 2 litre diesel BMW and average 43mpg (about 550 miles to £80) however on a long run I can extend that more towards 47mpg (closer to 650 miles) however I find that my driving style changed due to my job and I guess, maturing. Gone are the days of being slightly aggressive with the car and now being smoother. I havent noticed a dramatic increase however I live in a city, commute out through city roads to dual carriageways to B roads.

I maintain if I get a job in the city I will probably commute by walking or cycling however I would look to sell my heavy and cumbersome diesel and buy a more modern petrol as I will be doing 10 minute trips to the shops and back more often.

Maybe Im wrong but for those short journeys a lighter petrol car will probably warm up quicker and handle the stop start of city life better and more efficiently than a diesel over a ten minute period. This is based upon the fact my car is 10 years old and recently I had a Skoda brand new 1.2 TFSI petrol for a few weeks that was averaging about the same MPG as my diesel when comparing fuel price difference.