MPG half of that advertised! How to get out of car agreement?

Strider590

=rizla= wrote: »

I think he's trying to say once its at m'way speeds you don't have to use fuel to accelerate a heavy car from 0mph to 70mph, obviously a car designed for a roads/m'ways gearing etc is designed for higher speeds, so at or beyond the limit a bigger car can actually give better mpg than a small city car.

Kinda........

The heavier an object is and the faster it is moving, the greater the force required to stop it.

I used headwind as an example, but a moving object effectively creates it's own headwind. The faster it goes, the greater the headwind. Remember a big car drags most of that extra weight behind where it's not creating extra aerodynamic resistance, so the two cars may have similar resistance at the front, but the bigger car has more weight behind it and therefore needs to use less energy to maintain speed.

This of course falls over when the big car in question is something like a 4x4 or crossover which are simply less inefficient in their weight distribution and aerodynamics.

=rizla=

But more energy to overcome the rolling resistance of the heavier car.

Strider590

=rizla= wrote: »

But more energy to overcome the rolling resistance of the heavier car.

Rolling resistance is nothing to do with weight, because of momentum. It's a friction not a force. Tyres, wheel bearings and scrubbing brakes create rolling resistance. Both cars have 4 wheels.......

If you clutch in on a small light car and a big heavy car next to each other at say 50mph, which one will roll to a stop first?

Lift both up on ramps and measure the force required to turn the wheels, that's rolling resistance and in that respect a small car with smaller diameter wheels actually has slightly greater rolling resistance.

Hanspence

Thank you ever so much for the constructive messages guys!

I am just wondering who is liable for these mpg figures. If, as said above, they are tested so they look good for speed and performance- surely that is false advertising?
I agree that I have little chance of getting out of this however consumers (me included) use the mpg figures to make an informed purchase. When these are hugely innacturate, someone must be responsible ?!

Strider590

Hanspence wrote: »

Thank you ever so much for the constructive messages guys!

I am just wondering who is liable for these mpg figures. If, as said above, they are tested so they look good for speed and performance- surely that is false advertising?
I agree that I have little chance of getting out of this however consumers (me included) use the mpg figures to make an informed purchase. When these are hugely innacturate, someone must be responsible ?!

It's just the way the industry is these days, they run the mpg tests on cars on rolling roads, with most of the interior stripped out, zero wind resistance and with an expert doing the "driving".

It's even come up on BBC Watchdog.

The fact is, consumers use things like MPG as an excuse to buy a new car, but very few ever go and check whether the figures are true and those that do often choose not to believe the real figures simply because they've fallen in love with the idea of a new car, and because the salesman "seemed so honest".

DUTR

Hanspence wrote: »

Thanks for your reply.

I did quickly research it and the good mpg seemed to be rather consistent.
It's actually a petrol, 0.9. So it should be incredibly efficient.
I called Alfa and there is no recalls or software updates that the car is missing, and it has been fully serviced from new.

Sorry I just re-read you went looking for a diesel but ended up with a petrol, however the figures still stand(ish)
Sometimes much of the fuel consumption is during heavy acceleration and this is more likely with a smaller engine than a larger more powerful one. That said I would have thought the Mito suits the 1.4 engine more so than a 0.9litre.
If you are accelerating gently at all occasions and the car is not loaded up, then I'd still 'expect' you to be getting mid 30 to mid 40 mpg.

Marktheshark

And the temperature question ?
Has it got a temperature gauge for the engine ?
Is it reading normal operating temperature.

Cornucopia

It's not the same on every car, though. The Honest John "percentage of claimed MPG" figure varies hugely from respectable 90%+ down to the 60%s.

nidO

Hanspence wrote: »

Thank you ever so much for the constructive messages guys!

I am just wondering who is liable for these mpg figures. If, as said above, they are tested so they look good for speed and performance- surely that is false advertising?
I agree that I have little chance of getting out of this however consumers (me included) use the mpg figures to make an informed purchase. When these are hugely innacturate, someone must be responsible ?!

The EC ultimately, as it's they who mandate the rules and requirements for testing cars to obtain official MPG figures.

You therefore have absolutely no comeback against the dealer who sold you the car or the manufacture, as you can bet your life they stick rigidly to the rules they're required to follow, its just the rules are very generous in how they allow MPG figures to be obtained.

That said, as far as consumers making an informed purchase goes, I would say this also comes down to educating yourself about the figures - I don't mean this as an attack, but it is widely accepted knowledge that manufactures' MPG figures are absolute "best case" and shouldn't be taken as reality (with real figures being readily available from most car websites, including honest john that's come up a few times in this thread), they are at best a measure to compare the different MPG against other cars, not as an actual figure to achieve.

As mentioned a number of times in this thread though, the MPG you're reporting is very on the low side even for real-world figures for your car, if you're happy that you're going to rule out the possibility of bad/inefficient driving on your part, you might want to get it checked over at a garage.

=rizla=

Strider590 wrote: »

Rolling resistance is nothing to do with weight, because of momentum. It's a friction not a force. Tyres, wheel bearings and scrubbing brakes create rolling resistance. Both cars have 4 wheels.......

I always thought it was directly proportional, I must be wrong, hey ho.


OP, its worth checking you haven't got one or more brakes binding on, a binding brake will destroy mpg.