Weight difference of two cars - can it impact fuel economy that much?

mumof2

I haven't got exact figures on how much mpg my friends Renault Grand Megane Diesel (Estate) does, but it weighs 1794KG unladen. (her car - http://www.renault.ie/renault-range/passenger-vehicles/megane/grand-megane/overview/index.jsp)

My own Ford Focus Zetec Diesel estate weighs 1885KG. (yr 06) (here is my same as my car
http://www.motornet.ie/usedcars/?make=Ford&model=Focus&submit2.x=15&submit2.y=28)

Not a huge difference (I expected a bigger margin after test driving Megane recently).

My question is where can I get exact figures on fuel consumption and does this difference in weight really save on fuel costs?

Im looking to trade in my own again (only have it since October) as its really too greedy. I know fuel prices have gone up but it shouldn't cost me Eur 15 to drive approx 150KM surley????????????

Padraig Mor

Not sure about the Focus but the Megane is nowhere near 1794kg! Also, they are different engines so will differ in consumption. If your Focus has the geriatric 1.8TD lump, the 1.6D would be far better.

Guy:Incognito

Does the Renault site give the weight? I cant see it.

According to Parkers the Meganes weight is 1306kg

1800kg is a lot, that cant be right.

http://www.parkers.co.uk/cars/specs/Detail.aspx?deriv=44621

Matt Simis

Where are you getting these weights from?!
CarFolio says a Focus TDCI Estate is 1391kg:
http://www.carfolio.com/specifications/models/car/?car=167552

For reference an Audi S8 with a 4.2l V8 weighs 1750kg, how possibly could a focus or Megane weigh more?


On the actual cars in question, what engines in each?

mumof2

After looking a the Manual of the Megane, we were referred to a plate on the car, which is on the side of the door frame when you open the door. It read as unladen weight, then gave another figure of over 3000KG for fully laden with Trailer etc.

I automatically went to my car and checked for the same label and took the first figure according to her book and it read as above. However just pulled out my own manual and it gave pages of different weights but i think mine should weigh

1.6 l Duratorq - TDCi Manual Transmission - 1386/1391KG(not sure why the sticker/plate reads 1885KG)

Which means I've got the wrong info on the Megane too.

@Matt Simis - I completely agree with u as to how our 2 cars could weigh more:D Not possible!!

But unfortunately im still confused as to what the Megane rightly weighs, or should I go with the 1306KG according to Guy's figures? Even so for a 1.5 Engine in the Megane, weight wise thats not much difference, yet it felt much lighter on the road.

Where does this info leave me - which car would be better on fuel economy?

firefly08

Don't know about these cars in particular, but they say that whether weight makes much of a difference depends on the kind of driving. At speeds of up to around 40 mph, the biggest challenge for the engine to overcome is rolling drag, which is related to weight. Beyond that speed, it still matters, but aerodynamic drag kicks in in a big way, and dwarfs the effect of rolling drag. Since weight doesn't affect the aerodynamics, it shouldn't make much difference to fuel economy at high speeds.

So, at < 40, weight matters a lot, > 40 it starts to matter less.

This is just what I've read, I wouldn't bet actual money on it (but I can say that when I used to do a lot of motorway driving @80+ mph, I never noticed much difference in fuel costs whether I travelled alone or had 2-3 passengers)

Top Dog

mumof2 wrote: »

1.6 l Duratorq - TDCi Manual Transmission - 1386/1391KG(not sure why the sticker/plate reads 1885KG)

Maybe the 1885kg is the maximum allowable (safe) laden weight of the vehicle?

CiniO

firefly08 wrote: »

Don't know about these cars in particular, but they say that whether weight makes much of a difference depends on the kind of driving. At speeds of up to around 40 mph, the biggest challenge for the engine to overcome is rolling drag, which is related to weight. Beyond that speed, it still matters, but aerodynamic drag kicks in in a big way, and dwarfs the effect of rolling drag. Since weight doesn't affect the aerodynamics, it shouldn't make much difference to fuel economy at high speeds.

So, at < 40, weight matters a lot, > 40 it starts to matter less.

This is just what I've read, I wouldn't bet actual money on it (but I can say that when I used to do a lot of motorway driving @80+ mph, I never noticed much difference in fuel costs whether I travelled alone or had 2-3 passengers)

To what you said, I'd add one more thing.
When accelerating weight play cruicial role.
The more weight, the more energy you need to use to accelerate the car.
So f.e. it has big impact in city driving, when you are stopping and staring all the time. On motorway when you hit 130km/h and keep it for few hours, weight doesn't have too much impact.

Voodoomelon

I nearly had a heart attack at the weight of the Focus, thats exactly what my car weighs according to my last NCT, 1890kg. I thought these new cars are getting bloody heavy!

unkel

Matt Simis wrote: »

For reference an Audi S8 with a 4.2l V8 weighs 1750kg, how possibly could a focus or Megane weigh more?

+1

My BMW 7-series with the 3.5l V8 automatic was 1780KG. Small family hatches today are in or about the 1200KG

Edit: just looked it up: a base Golf weighs 1115KG, a base Focus 1170KG

All these weights are empty car (no driver or luggage)

shogunpower

2.8 long wheel base shogun weighed 1950kg when i cleared it, so theres no way a medium/small sized car weighs over 1500 kg.

mumof2

Top Dog wrote: »

Maybe the 1885kg is the maximum allowable (safe) laden weight of the vehicle?

Im not sure, but there was a second number under it of 3185KG - which according to the Meganes manual (which carried the same sticker with weights info) said this was the loaded weight of car including trailer.........anyhow thats not important. @ Firefly 08, thats actually very interesting reading!

My car is always empty - except on school runs morning and evening, never have stuff in the boot. (I know I can fit loads into the Estate boot on hols:D)

Just checking my last NCT docket to see if the weight shows up..........and.......ha got it: (Brake performance) Weight 1385KG:D

Nice one about the NCT Voodoomelon;)

12gauge dave

its rediculous the weight of cars since the ebd of the 90s!

from a performance point of view weight is a major major major factor

theyre hasnt been a proper performance hatchback in my opinion since the 90s and theyre never will again with all this technology rubbish:mad:

-Chris-

Ignoring the weights for a moment and focusing on the fuel economy, there aren't many cars that will give you enough of an MPG advantage over a 1.6TDCI Focus to justify the depreciation cost of getting rid of your car after 6 months.

Give or take, €15 will get you 10 litres of fuel.
If 10 litres gets you 150KM then you're getting 6.5-7l/100km.

Personally I wouldn't consider that particularly bad MPG.


One thing to note is that the Ford figure for your car is 4.5l/100KM on the combined cycle, so it is a good bit thirstier than Ford claim. It may benefit from a service or some mechanical attention.

mumof2

-Chris- wrote: »

Ignoring the weights for a moment and focusing on the fuel economy, there aren't many cars that will give you enough of an MPG advantage over a 1.6TDCI Focus to justify the depreciation cost of getting rid of your car after 6 months.

Give or take, €15 will get you 10 litres of fuel.
If 10 litres gets you 150KM then you're getting 6.5-7l/100km.

Personally I wouldn't consider that particularly bad MPG.


One thing to note is that the Ford figure for your car is 4.5l/100KM on the combined cycle, so it is a good bit thirstier than Ford claim. It may benefit from a service or some mechanical attention.

Thats interesting, didn't know that - wil mention it in the morning to the mechanic, have to go anyhow as the boot lock isn't working (and of course ist electronic:mad: (where are the good old days of using a key - but only have myself to blame - should have kept my first car - a 1991 Fiat panda:p)

Micheal H

-Chris- wrote: »

One thing to note is that the Ford figure for your car is 4.5l/100KM on the combined cycle, so it is a good bit thirstier than Ford claim. It may benefit from a service or some mechanical attention.

Manufacturers fuel consumption claims are usually considerably lower than the real world figures. As far as I know, when they test fuel figures they carry out a simulation of the typical urban/extra-urban trips. This will be done on a rolling road, for a set distance, at a set speed or variety of speeds. No hills, no corners, no unforeseen traffic jams and no weather.

So these figures are generally the best you could possibly hope to achieve and you rarely will ever get near them.

-Chris-

That's very true, but we're talking about the difference between 60 and 40MPG. It's significant enough that I'd at least get it looked at before I considered changing car.

Micheal H

Indeed, 40MPG is a little on the thirsty side for the size of engine and probably does warrant having it looked at. Certainly wouldn't expext it to get close to 60MPG though, except on a long downhill run with a good tail-wind

mumof2

The mechanic said he will put it through a test. Not sure if I can do it today, may be tomoro morning instead (wil take up to 2 hrs).

On another note, the mechanic said to stay away form Megane's unless ive got a new one with up to 100,000K Warranty! He said they can give fierce trouble and that my one would be better.

I hope the test comes back with some good info, he also gave me contact details of a towbar mechanic, (saving me another 250 eur!!), so I might just be able to keep this car after all:)