With the 2.0Tdi in my Octy i've found that to maximise mpg i need to keep above 2000rpm.

That means I use 3rd to 40mph, 4th to 55mph and 5th to 70mph before dropping into 6th. However because of the great torque, i've found myself block changing from 2nd to 4th and then 6th or from 3rd to 5th which really buggers up my mpg if I don't change at the right time..

3rd for me at 30 too. I tend not to use 6th unless i am cruising at motorway speed.

2nd if it's uphill, otherwise 3rd. Don't like letting the revs drop too far below 2000rpm -> 30 in 3rd = about 1850rpm, any lower and the engine gets too unresponsive for my liking...

Am I the only person who looks at the rev counter as opposed to the speedo first?(in the fabia and octavia)

Have no idea as to speeds in relation to gears :eek:(octavia does do 70 in 2nd though )

Am I the only person who looks at the rev counter as opposed to the speedo first?(in the fabia and octavia)

Have no idea as to speeds in relation to gears :eek:(octavia does do 70 in 2nd though )

I used to change gear according to the rev counter and it's the ideal way. Unfortunately as everyone is aware if you stray outside the speed limits by accident, there's now more chance than ever that the law is going to find out about it so the speedo is where my eyes are generally (when they are not on the road of course).

Indeed, some seem to be missing the point. Gearing controls revs and the amount of revs is what you should be looking at directly.

For any period, I would say 1500rpm minimum.

There is a scurrilous rumour on the SEAT forum saying that an Ibiza FR td at 2000rpm gives better economy than at 1500rpm!

Indeed, some seem to be missing the point. Gearing controls revs and the amount of revs is what you should be looking at directly.

IIRC, the OP's question was simply what gear are you in at 30mph....... surely it's immaterial what revs you are doing

I pretty rarely use the rev counter to change gear and tend to just "feel" when's a good time to change up or down. Very unscientific, but my mpg seems unaffected by it

Chris

I did indeed ask what gear - but I suppose revs is more important.

I live in the Fens, everywhere is flat. If driving in town with lots of junctions, parked cars etc - I will keep it in 3rd (about 2000 rpm at 30).

If just driving through the many villages which have no activity... 4th (about 1500rpm at 30).

I guess when cruising I've found that keeping it between 1500 and 2000 is the most economical, only going up to 2250 for accelerating. But think I'm going to try cruising at higher revs and seeing how I like it.

There is a scurrilous rumour on the SEAT forum saying that an Ibiza FR td at 2000rpm gives better economy than at 1500rpm!

I would say that that ties in with my experience, actually. There's not much in it between 3rd and 4th at 30, but try it switching between 5th and 6th at about 45mph. (Don't forget there's a 6 second lag on the 'instantaneous' mpg reading)

As far as I know, the reason for this illogical increase in mpg is to do with the ECU reducing the amount of fuel injected into the cylinder in proportion to the increased power provided by the turbo being on-boost above 1900rpm. So although the engine is turning faster at 2000rpm than at 1500 rpm (obviously), the ECU is injecting less than 4/3 the amount of fuel, so the mpg is better...

I think that's how it works, anyway!

I'm not sure that even makes sense to me now! :P

The computer must have been lying when it told me that my MPG was better in 4th than at 3rd at the same speed then....

Even though i was not using any more throttle in 4th than in 3rd... in fact maybe even less throttle.

In the end though, I got bored of concentrating on getting maximum MPG all of the time, when it was only a couple of MPG difference... ruins the driving experience for me... just drive it how you want, and dont let a couple of MPG here or there bother you, otherwise whats the point in having a Fabia VRS. Anyone who wants the best economy really should have bought a Lupo 1.4 TDI.

The computer must have been lying when it told me that my MPG was better in 4th than at 3rd at the same speed then....

I think it only applies at very particular speeds TBH. I've not tried it at 30, but the 45mph in 5th/6th test has worked for me. As it goes, I try to keep it above 2000rpm wherever possible, but this is for responsiveness reasons, rather than for economy...

I drive in whatever gear I fancy driving - if I want to be able to accelerate I don't drop it in the highest gear, if however I'm doing 30 mph on a flat road, not too much wind, etc etc it can do it in 6th. If you let the speed drop, or you have to even remotely accelerate 6th is the wrong gear. 3rd/4th is probably the sensible pair to choose from, 2nd will allow you to accelerate real quick to the point where you'd need 3rd anyway.

Either way - a lot depends on what you are trying to achieve, if you're in a hurry then the highest gears don't make sense. Just use the gear you want :P

errrrr i can sit at 30 in 6th not putting to much of a strain on the engine

Tried this today and you get better mpg in fourth then you do in six so no point

I lied about doing 30 in 2nd... Tried it today and it sounded well wrong!

I do 30 in 3rd.

Please tell me some of you are joking.

5th at 30mph?? Tried this today and the rev's sit at 1100rpm, you've absolutely NO control over your speed at all, and your labouring the engine...

As for 6th at 30mph, don't make me laugh, that must of been a joke

45mph is pushing for 6th in my car and again there's no point because the engine labours when you need to accelerate. I stay out of 6th until i'm doing 70 just to keep up the economy.

I agree, with walkie, like to keep the revs above 1800 so you have the torque power when you need it, whatever gear satisfies that... better to be in control, avoiding small children and rabbits, oh and cats too, and other random stuff like that...

I agree, with walkie, like to keep the revs above 1800 so you have the torque power when you need it, whatever gear satisfies that... better to be in control, avoiding small children and rabbits, oh and cats too, and other random stuff like that...

Try 5th gear at 30mph tomorrow, you will be truely shocked I promise you :eek:

I use 4th. Sometimes I stick it in 5th if im cruising at 30 and not accelerating / decelerating. Engine doesn't sound like its struggling at all, but it does if I try and speed up.

Please tell me some of you are joking.

5th at 30mph?? Tried this today and the rev's sit at 1100rpm' date=' you've absolutely NO control over your speed at all, and your labouring the engine...

As for 6th at 30mph, don't make me laugh, that must of been a joke [/quote']

Hi

No joke. Why have you no control over the speed in 5th at 30mph? The engine is working above idle speed, so your throttle use will control the speed. Even my newer learners can regulate the speed in 4th at 30 and 5th is not much more difficult. You use your observational skills to help you anticipate when you will need to use a lower gear for acceleration or engine braking and change gear as appropriate.

Why is the engine labouring? You are asking very little of the engine doing 30mph, so you just cruise on a tiny amount of throttle. Labouring an engine is when you ask for a lot of power from too low an engine speed. Again, observation and anticipation are all you need to change to an appropriate gear so it is ready just before you need it.

Basically at 30mph on a level surface, if you cruise in 3rd, you will see significantly less MPG than if you cruise in 4th and the improvement from 4th to 5th is less, but still significant.

The driver should always be in an appropriate gear for the conditions. Here in Essex, we have large areas of 30mph road whith nothing going on at all. Here, where conditions permit, 5th at 30 is fine. Just change down when I want to accelerate.

In efficiency terms, if you are sat at 1900rpm in 3rd, you are filling and emptying your engine with air 1.7 times more often than in 5th at the same speed. You therefore need to compress 1.7 times more air to TDC. This is called pumping losses and in a diesel, it having no throttle valve, this is relevant.

Next you have the added 1.7 times further for the engines moving parts to travel for an equivalent distance at 1.7 times the speed. Drag and viscous drag increase with engine speed. These are frictional losses.

Last and by no means least, the most efficient combustion is when an engines output is high in terms of MEP (mean effective pressure). When you apply the gas lightly in 3rd at 30mph, you are requesting a tiny amount of torque from the engine, and consequently adding tiny amounts of fuel to the air in the cylinders. That fuel has to burn to produce engine power. When it burns, the energy has to fill several routes of dissipation. Obvoiusly, it has to cause a rise in pressure to drive the piston downward. Less obvoiusly, it has to heat the air that remains uncombined with the fuel. It has to heat the cylinder walls and it has to contribute to overcoming the engines internal friction. It also has to compress the air in the cylinder next lined up for combustion.

For all these factors, a smaller amount of fuel in the cylinder will leave a larger percentage of the fuel used to feed the losses which are very nearly "fixed overheads" in enery terms. If you fill the cylinder with a little more fuel, increasing cylinder output per stroke, the losses account for a smaller total of the engines fuel consumption.

I spent a few curious minutes today playing with the cruise control in 30 limits and found that, conditions and gradients permitting, 5th gives best economy at constant 30mph. 3rd is good for around 40mpg at 30mph, 5th good for around 70mpg at 30mph. Curiously enough around a x1.75 improvement, which, if you apply the losses outlined above, is pretty close to what the theoretical advantages would be.

Of course, in the cut and thrust of city centre traffic, where instant resonse is required at short notice, 3rd or even 2nd could be called for as a cruising gear.

There are of course times when lower revs or a particular lower engine speed could make for higher fuel consumption, particularly where the engine is in a flat spot where cylinder filling is very poor.

Chris

It can do it in 6th - and as per a post I made a few posts up - if the car is labouring (read: I am accelerating, going uphill, or the car is heavily loaded) I wouldnt be in that gear.

In 6th at 30mph it will accelerate if you are cautious, but it's not the thing to do. The car isnt struggling with it at all though.

As long as you stay above the anti-stall revs, no problem

Most of the time I drive in 4th in a 30 mph zone where I need to change speed up/down because of junctions etc, if it's a medium stretch of road probably 5th, or 6th if conditions are right.

Chris summed it up much better than I can (be bothered to repeat :P ) so will leave it at that

5th gear :thumbdwn: each to there own, but I am still finding it hard to believe, must give it another try today...

Definitely 3rd unless it is an open road then mabye, just mabye, 4th. All the advanced driving courses and the AA,RAC recommend 3rd gear in 30 zones for exactly the reasons stated previously, more precise control of the throttle and possibly better mpg. You have very limited throttle control in 4th at 30.

Dont have any trouble controlling the throttle myself, as I'm keeping it at a fixed speed. If I accelerate I change cogs for sure.

MPG wise if you're not accelerating the higher gears will be best, for ability to increase speed a lower gear is of course better.

Thing is, I find that in 30 mph zones the only thing you do is either do 30mph, or continually accelerate/brake. If it's the latter it's the low gears.

I must say, after trying it this morning, it just doesn't feel right at 5th. I like to know that if I put my foot down the car will actually accelerate, not just make more noise. I also don't want to be in a situation where I have to scramble for a lower gear...

I definitely find 4th great at 30 in the Furby. It sits at around 1600 rpm, which leaves plenty of available power and excellent economy.

The Fabia vRS is the first car I have driven where 30 in 4th is ok, my dads 1.6 Xsara for example is much happier in 3rd.