Save £800 a year on petrol...Guardian article.

alastairq

what amazed me about the article, were the responses below it.

What an amazing amount of ignorance and urban myth there is driving around out there.....

Anybody remember [or were driving] way back in the 1970's when the Oil crisis occurred, and the government imposed a blanket NSL of 50MPH? Plus, issued fuel rationing coupons?

Strangely, today's government advice and figures differ little from those of 30 years ago...ie at 50mph one saves up to 20% of the fuel used at 70mph.

This, despite the fact that the vast majority of today's cars are running around using fuel injection, and electronic engine management systems which are capable of optimising fuel consumption........and in the 1970's, nearly all cars used carburettors....which despite their clever engineering could not hope to match today's fuel figures.

I don't drive a 'modern' car.....[I make my savings in not having to concern myself over depreciation and interest rates]

My usual daily drive is one of those old, huge Volvo's, that drivers and riders so detest.

As such, the old car is capable of achieving consumption figures below the 20mpg mark.

If little thought is given to the appropriate style of driving!

However, I give 100% thought to my driving, and consistently achieve over 30mpg's.

If I get in anybody's way, more often than not it's because they have no intention of complying with the law.
I envy those who achieve 50 or 60 mpgs.....or more......but not their other costs.

As for tailgaters...well....they're so far behind my head I have to squint to see them in my rear view mirror.

Besides, my back bumper isn't of the plastic kind, so will deploy their airbags if they cannot out brake me. Maybe my back bumper should carry an appropriate health warning?

I have one problem with the concept of forward planning, and simply coming 'off the gas'' earlier, to slow.

That is, with my car [a 740 volvo] it's such a heavy lump, yet has such amazing aerodynamics, that from around 60mph, it takes more than 3/4 of a mile to slow to 30, in top gear, naturally.....so I invariably end up using the brakes for the last bit of speed adjustment......

On a strange road, I probably cannot see 3/4 mile ahead....

somech

easy way to save cash and fuel

drive less walk more works for me

thescouselander

What rubbish advice -

He tells me I should instead drive along speed-humped roads at a steady 15-20mph.

You might save a bit on fuel but be prepared to fork out a fortune fixing your suspension.

forgotmyname

Kilty wrote: »

Not doing your DPF any favours either if your car has one.

Mondeo diesel 2004, No DPF but it has a CAT which will be removed when it goes in for any work.

Why fit a cat to a UK diesel? It doesnt make a lot of difference to the emissions but drops a few MPG. The extra few mpg would equal out the emissions.

Trip computer said i was doing 38mpg, I filled up and reset it. What a shock it is suprising how much you press the accelerator to gain speed and watch the mpg figures drop like a stone.

Accelerating gently & lifting off a lot whilst cruising got my mpg upto 62. Well thats what the computer says but it does tell lies.
Approx 50mpg? Not used the £50 worth i put in yet so cannot work out the true mpg figure.

Driving by the computer does help. MPG drops by 0.1 i lift off to let it raise again. Too many short journeys from docs & shops has dropped it down to 54 now.

tomstickland

There's no way I can drive at 20mph over speed bumps. I have to slow to around 5-6mph. I'd rather spend the money on fuel than replacing suspension components.

Strangely, today's government advice and figures differ little from those of 30 years ago...ie at 50mph one saves up to 20% of the fuel used at 70mph.

This, despite the fact that the vast majority of today's cars are running around using fuel injection, and electronic engine management systems which are capable of optimising fuel consumption........and in the 1970's, nearly all cars used carburettors....which despite their clever engineering could not hope to match today's fuel figures.

It doesn't matter how clever the fuel injection is, it will always require more power to drive at a higher speed due to the increase in drag forces.

Modern vehicles are heavier and larger than those from a few decades ago too.

motorguy

Kilty wrote: »

OMG.

What kind of roads is that on? And I assume it's a diesel?

Its a passat 2.0TDI CR Bluemotion.

On average i'm getting 67.7mpg over the course of a tank.

The route was 6 miles A class roads, 16 miles of motorway and a mile across an industrial estate.

Oh, and its not down hill...

alastairq

most, but not all, speed hump-type traffic calming measures are within 20mph speed limits.

The point being made with the given advice is that...rather than accelerating smartly up to the speed limit, only having to brake smartly to avoid grounding on the speed hump....just increase speed steadily..maybe not up to the limit..maybe just up to a speed which will enable you to slow more gently to cope with the next hump.

There is no legal compulsion to drive up to the speed limit..whatever it is....

As for creating a so-called 'delay' to following traffic?

what is more important to you, the driver?

Your wallet?

Or the other drivers' egos?

[My view is..if the vehicle behind wants to move faster, then they can overtake.

Which they wont want to do because it makes them stand out , for what they are...]

After all, we are only talking minimal speed differences...especially within a 20 mph limit.

skiddlydiddly

alastairq wrote: »

what amazed me about the article, were the responses below it.

What an amazing amount of ignorance and urban myth there is driving around out there.....

Anybody remember [or were driving] way back in the 1970's when the Oil crisis occurred, and the government imposed a blanket NSL of 50MPH? Plus, issued fuel rationing coupons?

Strangely, today's government advice and figures differ little from those of 30 years ago...ie at 50mph one saves up to 20% of the fuel used at 70mph.

This, despite the fact that the vast majority of today's cars are running around using fuel injection, and electronic engine management systems which are capable of optimising fuel consumption........and in the 1970's, nearly all cars used carburettors....which despite their clever engineering could not hope to match today's fuel figures.

I don't drive a 'modern' car.....[I make my savings in not having to concern myself over depreciation and interest rates]

My usual daily drive is one of those old, huge Volvo's, that drivers and riders so detest.

As such, the old car is capable of achieving consumption figures below the 20mpg mark.

If little thought is given to the appropriate style of driving!

However, I give 100% thought to my driving, and consistently achieve over 30mpg's.

If I get in anybody's way, more often than not it's because they have no intention of complying with the law.
I envy those who achieve 50 or 60 mpgs.....or more......but not their other costs.

As for tailgaters...well....they're so far behind my head I have to squint to see them in my rear view mirror.

Besides, my back bumper isn't of the plastic kind, so will deploy their airbags if they cannot out brake me. Maybe my back bumper should carry an appropriate health warning?

I have one problem with the concept of forward planning, and simply coming 'off the gas'' earlier, to slow.

That is, with my car [a 740 volvo] it's such a heavy lump, yet has such amazing aerodynamics, that from around 60mph, it takes more than 3/4 of a mile to slow to 30, in top gear, naturally.....so I invariably end up using the brakes for the last bit of speed adjustment......

On a strange road, I probably cannot see 3/4 mile ahead....

Engine efficency has improved a lot but the laws of physics have remained constant.The faster you go the more power is needed to overcome air resistance and it isn't linear.For exampe car A might only need 50bhp to do 100mph but 500bhp to do 200mph.As more power created is more fuel burned then slowing down to 50mph would save a lot of fuel.

We use 2.5l diesel vans at work and I've seen the figures to back up these claims from before and after with drivers having fuel efficency instruction.Some went from 17mpg to over 40mpg driving a set route.This is an extreme case though and most went from low to mid 20s to low to mid 30s.

After a bit of searching on drag coefficients I found this:

Volvo's Frasher says the force acting against a car by the air it moves is a function of:


Cd x Frontal Area x Density of Air x Speed Squared
Speed clearly is an important part of the equation. At stop-and-go speeds, drag isn't a big deal, but the faster you go, the more it matters. At 70 mph, you've got four times the force working against your vehicle that you have at 35 mph.


BTW-a volvo 740 has a drag coeff of 0.4 which is very very high by modern standards, maybe your accelerator pedal is stuck .

Niowrtt

I spent three hours a day driving around 30,000 miles a year so got pretty obsessed with fuel efficiency.

The key to getting better economy is to track what you're getting for different driving styles. Every car and type of trip and even weather has different requirements. Eventually you teach yourself best techniques by experience.

skiddlydiddly

A basic tip is use the lowest amount of revs in the highest gear possible without labouring the engine.If you are getting excessive judder in the pedal you're in too high a gear.If you are having to apply a lot of throttle on hills to maintain speed then its probably better to gear down, you may have higher revs but will be using less fuel.

You just have to think about what you are doing and put your ego to one side and realise most of us can improve quite a lot.Once you get into the habit it becomes second nature.

BTW an added bonus is that it also can save on other components like brakes-I barely brake now in comparison to before and do significantly less gearchanges so less wear on the clutch and drivetrain. If you do big miles this will affect you even more.