i always drive on 5th gear when doing 30mph on my 1 litre polo, will that help save fuel or will it take more?

I've always been told that 5th gear doing 30mph (aslong as you are just cruising, not slowing and accelerating) is the most efficient way of driving

i always used to

if the car is judering no your wasting fuel.

if the car is judering no your wasting fuel.

which is why i dont do it in my valver as the gearing is longer than it was in my mk2

you use the least fuel when the engine is at it's most efficient load. Whether or not this is 30mph in fifth depends on your engine and (more so) your gear ratios. But in general at 30mph in a petrol engine car you are labouring the engine and would actually be using less fuel by changing down into 4th. It'll also cause less engine wear and less carbon build-up too. Generally the sweet spot is probably between 1500 & 2500 rpm in a petrol engined car. You can buy vacuum gauges which usually have marks on the dial to indicate whether the engine is running in it's sweet spot or not.

This is a generalisation as there is no single rule that covers all cars, all engines and all conditions but it's probably not far off.

i just run around in second everywhere which explain why i get 25 mpg

you use the least fuel when the engine is at it's most efficient load. Whether or not this is 30mph in fifth depends on your engine and (more so) your gear ratios. But in general at 30mph in a petrol engine car you are labouring the engine and would actually be using less fuel by changing down into 4th. It'll also cause less engine wear and less carbon build-up too. Generally the sweet spot is probably between 1500 & 2500 rpm in a petrol engined car. You can buy vacuum gauges which usually have marks on the dial to indicate whether the engine is running in it's sweet spot or not.

This is a generalisation as there is no single rule that covers all cars, all engines and all conditions but it's probably not far off.

In addition to this it depends on where you have you foot on the throttle. Obviously this ties in with what is mentioned above, if the engine is running efficiently and not struggling you can get away with a minimal amount of throttle (a vacum gauge makes you notice this more encouraging you to drive more efficently if your after mpg) Coasting upto junctions in gear with no throttle and no braking also saves fuel, might annoy people behind you though...

Yeah keeping it in 5th will save fuel... I do it all the time around towns and villages - There's no need for acceleration and generally you won't need to brake if you keep far enough behind a car that may be pulling into a side road. If mine drops below 1,400rpm in 5th i'll kick it into 4th. Tbh you should just drive around towns etc between 1,400 and 1,700...Not really any need for any more in my opinion.

Also curious...Seen about people putting "iirc" in their posts... What does it stand for!?

if i remember correctly

Cheers bud

if your driving around with hardly any throttle input. Then thats the most economical.

If your half throttle in 5th at 20-25 and the engines labouring your using more fuel than if you were in 4th, slightly higher rpm and less throttle. Simples

Another point in saving fuel, when you're slowing down, do you use less (or close to none as JC says) fuel if you change down the gears and use engine braking than if you knock it into neutral?

I always thought it does because in effect it's the speed of the car and the wheels turning the engine over, not the fuel input so it wont use any but my dad pointed out that if the engine speed is higher, even if it's because of the wheels turning the engine over, the fuel will still be injected at that rpm and will use as much fuel.

But then I pointed out that the throttle wont be open cos your foots not on the pedal but then that's just the air input right? (for injection engines)

Feel free to enlighten me on this and/or anything I've got wrong :)

if your really fast at changing down gear you'd get away with engine braking and using no or little fuel.

If your lazy though it drops abit of fuel in to keep the engine running as the rpm returns to idle.

When you lift off, say from 5k for example...Most engines, i know mine does, throws no fuel back in until it reaches around 1000 rpm when the idle wants to kick in.

The throttle butterfly if you like, is closed in idle position - just enough air to keep the engine running when its sub 1000 rpm.

Awesome, yeah I thought so, thanks Neil.

i heard when at a gearbox specialist that it can cause extra wear on the gearbox being in such a high gear when potiling around town etc.

i think he said its because your putting extra strain on the teeth and diffs irc don take my word

I've always thought that the more throttle you use the more fuel you use, not the more revs as that counts the amount of rotations that the engine is doing not the amount of fuel or fuel/air mixture that is being used. Am i right? and do you really want to be thinking ooooooo the car 300 yards in front of me might go down that sideroad i better get ready to change down a gear or two to compensate and avoid stalling? cos surely thats quite stressful? and you aren't ready at all times for a sudden speed change that may be dangerous when you think about it and come on do you want to be like a granny in a micra? 3rd ftw!

its a combination of both revs and throttle. imo, the engine is most efficient at peak torque, thats what i try to aim for when cruising. managed 54.4MPG from a mk2 golf 1300 on a recent long run, so must be doing something right?

not having enough CC's though

Makes sense chris. And the golf looks so sick in your avatar