Can someone explain something?

Tommy B · 24 Dec 2006 at 14:51

I drive a 1.4 Golf, which has a god-awful 0-60 time of something like 12 or 13 seconds. I have friends who have similar cars like 1.4 Clios, Corsas etc etc

Whilst their cars have a faster 0-60 time on paper, all my mates claim that the Golf is much, much quicker at accelerating at faster speeds. For example, doing 30-50 in the Golf would be faster than doing 30-50 in the Corsa, even though the Corsa's 0-60 time is significantly less. Is this true with cars of this sort of performance?

Secondly, does coasting actually save petrol? A have a friend who really bugs me because of his obsessive petrol-saving habits. This bloke puts the gear in neutral and coasts just about everywhere he can. I'm the opposite, I like putting the car in the lowest gear possible and always having the ability to accelerate

Faithless · 24 Dec 2006 at 14:54

First one, no idea. I doubt the Golf is actually quicker unless its momentum thats aiding it!

Second one. Two sides to this coin. Coasting is not as economical as engine braking (slowing the car down whilst in gear). If you put the car in neutral and coast, the car is idling therefore using fuel. However, with the car in gear and the foot off the pedals, the fuel at the injectors is cut (as in, no fuel will be used).

BUT, you will travel further coasting than you will with engine braking, so its 6 and hald a dozen tbh.

Scarfacé · 24 Dec 2006 at 14:56

If the car is in gear and is coasting, the car will not use any fuel at all.

If the car is in neutral then petrol will still be used to let the car idle.

Not to mention in neutral you don't have the help of engine braking, which will increase braking distance.

If the power figures of the cars are similar the difference between them is probably a combination of weight and gearing.

wassap · 24 Dec 2006 at 14:56

a lot is down to the way the engine is tuned, low down torque, or torque up in higher revs.

Also the golf is a very heavy car, and the clio and corsa are not, which gives them a significantly superior power to weight ratio.

moss · 24 Dec 2006 at 14:57

No the smaller cars with same sized engines will 'generally' be quicker acceleration from any speed, although its not really that simple.

Coasting doesnt really save petrol either, it will use a tiny bit less than having the accelerator pressed in, but there will be near to no difference. Once your foots off the accelerator with the clutch up no petrol at all is used, except when you either go into nuteral or put the clutch in and coast as it needs a supply of petrol to keep the engine running.

dirtydog · 24 Dec 2006 at 14:58

Tommy B said:
I drive a 1.4 Golf, which has a god-awful 0-60 time of something like 12 or 13 seconds. I have friends who have similar cars like 1.4 Clios, Corsas etc etc

Whilst their cars have a faster 0-60 time on paper, all my mates claim that the Golf is much, much quicker at accelerating at faster speeds. For example, doing 30-50 in the Golf would be faster than doing 30-50 in the Corsa, even though the Corsa's 0-60 time is significantly less. Is this true with cars of this sort of performance?

Seems doubtful when their cars are smaller and lighter than a Golf, I presume - due to being in the class below.

James07 · 24 Dec 2006 at 14:58

I know the GTI and the GDTI (I think thats the short version, the turbo diesel version) I know they are a lot faster cars, but i think thay are fast from start to be honest.

Gilly · 24 Dec 2006 at 15:00

James07 said:
I know the GTI and the GDTI (I think thats the short version, the turbo diesel version) I know they are a lot faster cars, but i think thay are fast from start to be honest.

You mean GTTDI?

Those two cars you name are very different to the one in the OP.

CypherPunk · 24 Dec 2006 at 15:02

In a modern fuel injected car you will save more petrol by bringing your foot off the throttle and leaving the clutch up and the car in gear than you will by coasting, see my post here.

Tommy B · 24 Dec 2006 at 15:03

OK.

So, putting the car in neutral and taking your foot off the clutch uses more petrol than having the car engaged in a gear and also having your foot off the clutch but without pressing on the accelerator?

So what happens if you're in, any gear, and just dip your foot on the clutch and take your foot off the accelerator whilst moving? Does that damage the engine?

Isn't the Golf a different class of car to things like Clios and Corsas? I'm not boasting as the Golf is my mum's. It's just all my friends have commented on how fast the car can accelerate at mid speeds using 3rd gear.

CypherPunk · 24 Dec 2006 at 15:12

Tommy B said:
OK.

So, putting the car in neutral and taking your foot off the clutch uses more petrol than having the car engaged in a gear and also having your foot off the clutch but without pressing on the accelerator?

So what happens if you're in, any gear, and just dip your foot on the clutch and take your foot off the accelerator whilst moving? Does that damage the engine?

Yeah, if the clutch is disengaged or the car is in neutral then the engine speed will fall back to idle and the ECU will begin injecting fuel again, this is also dangerous as you don't have full control of the car.

Disengaging the clutch while moving is know as coasting, and again it uses more fuel than driving in gear without touching the accelerator, not only that but it will also place unneeded strain on your clutch release arm and bearing.

dirtydog · 24 Dec 2006 at 15:15

Tommy B said:
Isn't the Golf a different class of car to things like Clios and Corsas? I'm not boasting as the Golf is my mum's. It's just all my friends have commented on how fast the car can accelerate at mid speeds using 3rd gear.

Yes it is in a higher class, but not a higher performance class.

Hawk Tuah · 24 Dec 2006 at 16:59

Well, there's two factors. The power output of your engine's and the weight of your cars.

All engines being equal, your mates lighter cars will accelerate quicker at any speed than yours. The golf is a nicer car though.

At the end of the day, performance aint everything. Well I say that, but thats just something people with slow cars say to make themselves feel better. Oh yer, economy.... Yer yours is probably less economical too due to your more weight. Oh well. Residual values. Yer you should win at that one.

Malachy · 24 Dec 2006 at 17:17

cant believe we are discussing how a 1.4 golf accelerates.

its slow, end of story!

put it in whatever gear you fancy and race against your mates all you want but its still slow it never will be fast.

however if it gets you from a to b then thats all that matters.

[TW]Fox · 24 Dec 2006 at 17:20

Tommy B said:
Isn't the Golf a different class of car to things like Clios and Corsas?

Yes. It's larger and heavier. This is why, in 1.4 litre form, its performance is woeful. Even the 2.0 GTI isn't exactly swift. If it's a Mk4 Golf and it doesn't have a turbo (ie, a TDI 130, 150 or 1.8T) or more than 4 cylinders, it's just slow.

Tommy B · 24 Dec 2006 at 17:36

I'll have to find myself a new car then.

The reason I'm confused is if I'm driving along and I dip my foot on the clutch, the rev counter goes right down. But if I just take both feet of both pedals, the rev counter stays high, which suggests to me it must be using more petrol.

[TW]Fox · 24 Dec 2006 at 17:38

Tommy B said:
The reason I'm confused is if I'm driving along and I dip my foot on the clutch, the rev counter goes right down. But if I just take both feet of both pedals, the rev counter stays high, which suggests to me it must be using more petrol.

When you dip the clutch, the engine idles becuase it is no longer connected to the gearbox. Therefore, you are using fuel to keep the engine ticking over.

When you lift off completely, the fuel supply to the injectors is CUT OFF - no fuel passes into the engine, and the momentum of the car keeps it turning. It uses no fuel.

RPM does not equal Petrol Used.

Tommy B · 24 Dec 2006 at 17:40

[TW]Fox said:
When you dip the clutch, the engine idles becuase it is no longer connected to the gearbox. Therefore, you are using fuel to keep the engine ticking over.

When you lift off completely, the fuel supply to the injectors is CUT OFF - no fuel passes into the engine, and the momentum of the car keeps it turning. It uses no fuel.

RPM does not equal Petrol Used.

Awesome.

I can't wait to prove my mate and his anal fuel saving methods wrong

Cheers everyone

Malachy · 24 Dec 2006 at 17:52

Tommy B said:
Awesome.

I can't wait to prove my mate and his anal fuel saving methods wrong

Cheers everyone

how this works on a modern car is very simple, your car will have a Throttle position sensor (TPS) this tells the ecu what position the throttle is in,

basically the ecu is coded so that when the throttle position is closed and engine revs are above 1500rpm (or whatever the ecu is coded tom, usually about 1500) then the injectors will stop squirting, this aids with engine braking.

its called "over run fuel cut"

however you saying you sit in the lowest gear possible is not exactly economical either and will be far less than your mates 'anal' and frankly dangerous coasting method.

DanTheMan · 24 Dec 2006 at 18:08

Don't you get taught nowadays to just stop at lights and such in the gear you're in? So effectively you should be driving more economical than your petrol-saving friend?