six speed gearboxes

"DervMan" gurgled happily, sounding much like they were saying:

Last time you were following some bimbling f****it...?

Have to admit, I'd like it to be a shade higher. First's too low to be much use other than first pulling away.

Pfft! Hardly. I've spent the month at HGV speeds apart from one moment of not caring so much about consumption. "Oooh 57, nudge cruise down one, there you go."

What I have discovered is that no matter how slowly I drive*, there's always somebody slower; usually just pulling out a half mile ahead. I swear the Saab looks _loads_ quicker at 60 compared with 50.

"DervMan" gurgled happily, sounding much like they were saying:

Ah.

So - f'rexample - on my trip back from Richmond-upon-Thames yesterday evening I would have shaved, umm, _considerable_ time off you doing the same trip...

:)

The slightly-as-I-expected thing is that it's made almost jack all difference to the commute. It's 29.5 miles home. Door to door it's still an hour, plus or minus five minutes. That includes 15 minutes of walking. So basically the driving takes ~45 minutes. The time difference isn't during the drive home, but at the York end.

If I were a geek I'd test my theory that by driving quicker and arriving at York earlier, I get snarled up in more traffic leaving the city or also arriving earlier. By relaxing, I arrive at the outer ring road later, which is quieter, as are the junctions, lights and roundabouts, so I make up the time.

Also, on main roads, driving at HGV speeds means you are not help up by so much if somebody driving at 43 mph pulls out in front of you. Compared with aiming for that speed where the whole speedometer illuminates.

What is the benefit of skipping gears? I read at a later post by DervMan that he is economising; what's the method?

I have read here in the past about a VW experiment that showed that one is best accelerating at full throttle but have found no backing evidence. Also, full throttle till the gear runs out/you have reached the desired speed, or until you reach a certain (car-dependent, I guess) number of revs?

Thanks,

Kostas

p.s.: I have a Focus and an Almera, both 1.8 petrol. The Almera has noticably shorter gears and I like it more, but would perhaps benefit from an additional (so, no regearing of the existing ones) sixth for economy and comfort.

The last two posts are barmy! Every engine has a particular no of revs which is best for fuel consumption and another for pulling power.

The whole point in having a gearbox is to match the speed with the perfect revolutions - the more gears the closer the approximation.

Skipping gears just means for part of the time the engine is not at its best efficiency, and is lazy.

Furthermore if you are in the wrong gear when you need either a burst of speed or some engine breaking - then you have an added function (changing gear) to perform when you least need task loading.

Why so? Up to ~30, up to ~60, select top, job done.

By your methodology, this technique works. High engine speeds in first and second (and the 2.0 six cylinder needs revving out) then select top for low fuel consumption.

And this was done.

No. In this case, the individuals concerned are accelerating to a speed that is inside or at the maximum in second gear. It's not wasting effort and transmission wear just using those gears they need.

Engine braking? But here you're missing the point.

The driver wishes to use all available performance until reaching a cruising speed.

It's energy management.

Some people call it hypermiling. I'm not a hardcore hypermiler (I don't spend long periods descending gradients with the engine off, for example). For me, it's short shifting (changing up at ~2,000 rpm), moderate speeds, anticipation, lifting off at the 450 yard point approaching a hazard (typical lift off for a level road at ~55 mph, adjust for wind, gradient and car load), turning the donk off at traffic lights, making sure the tyre pressures are not low. And other stuff too.

In numbers, a less energy-management aware driving style during my commute yields somewhere around 36 mpg. Driving with Miss Daisy in the back shows around 40. I find that the difference in time is trivial over the hour, door to door (including fifteen minutes walk) - getting into York in the evening, the final three miles can take anywhere from 5 to 15 minutes.

My best method for reducing fuel consumption is still, however, not using the car as much. :-) My motorway commute covers 285 miles a week. I get decent mpg figures using the motorway, but I can cut the overall miles by 30 a week if I use an alternative A road route instead. Although I see slightly poorer mileage, I'm using less of the stuff, so there's a saving here. I also save time, as it's shorter and as I'm driving at the same speed (~55) it's quicker.

Ooooh mighty saving of around 3 litres a week using the A road.

Then there's the city driving I used to do most weekends or weeknights. Variable mileage but usually around 30 a week. Only my Saab is thirsty in the city, returns under 30, even with me driving her. So that's another 6 extra litres a week I'm not using.

Yeah, thinking about it, the saving is somewhere around 12 litres a week by changing my driving habits. Somewhere about £600 a year, which in the grand scheme of things isn't much - but it does pay for the insurance and VED.

That may be efficiency versus economy: most* petrol engines are at their most efficient at full throttle. All this means is that the fuel required to produce peak power at full throttle is less as a proportion of the fuel needed to produce less power at a part-open throttle. I didn't put that very well.

Quite possibly in a labatory, but when I've tried this in real life, it didn't work. ;-)

There you go! Is it something like 22 mph / 1,000 rpm in top? Or even shorter?

I had a Honda Accord for a few months, which was geared to be just over 20 mph / 1,000 rpm in top. It wasn't noisy - that engine was remarkably smooth and quiet - but it wasn't very economical.

Just under 2000 rpm on mine. The beauty of a decent auto. ;-)

Meh - the quality of the transmission isn't the same as its final drive...

What I meant is a manual that needs a gear change when you hit a gradient on a motorway at 70 mph would be pretty boring. Doesn't much matter with an auto.

I think you need to try a crappy-changing automatic. Maybe an early 90s Rover 600? :-p

Dunno. I do remember trying an 825 after the SD1 - it had some form of early robotised synchro box from Honda and was distinctly unimpressed.

I am referring to this below.

Must be fun without PAS and servo brakes. :-) The Focus manual warns repeatedly about potential damage if switching off while the car is still moving.

I am a bit confused, but is this how one gets all available performance, as you say above?

Here is an empirical finding from the Almera (1.8 petrol, I repeat) o/b trip computer: by pushing up the revs in lower gears, I accelerate for less time, then being able to cruise at the required speed for longer (potentially skipping a gear or two).

I am not sure that my empirical finding is correct, and I am not sure if/at which point the revving gets too frivolous; the Almera kicks noticeably forward as it passes 4,000 rpm.

Also, the o/b computer shows *very* little fuel consumption irrespective of speed and gear when off the throttle (thought I would link with the hyper-miling technique you mention above.

Well, that may be hard to find out, as wifey confiscated the Almera, having realised what fun it is on 1st to 3rd on suburban roads. She is not a petrol-head; in fact she is the first driver (should I use inverted commas around driver? :-)) in her family; I was genuinely surprised!

From memory, the Focus 1.8 petrol is geared at an indicated 25 mph /1,000 rpm on fifth.

Kostas

Not as hard as you might think - when rolling, the steering wheel remains light. The braking system has enough vacuum for some use. But it isn't something I'd recommend.

Having run out of petrol on the motorway before (shudder) the car isn't difficult to stop.

No, it's a different discipline - that's not something I can do when short shifting.

Ya: that's block changing up.

Quite - probably not worth even trying to find it this side of too much time and a laboratory kicking about, either.

The low pressure turbo makes it easy to short shift and use the high gears.

Yes - that's the coasting in gear, where the ECU shuts the fuel supply down. It starts squirting fuel back into the engine as the revs drop and most inject fuel when the a/c compressor is running.

:)

That sounds about right: the 1.6 is close to the 9-3's 30 / 1,000 in top...

The 623GSi's box I used to borrow was exceptionally jerky. Every change caused a head bobbing moment.

The American iron we usually hire has a dumb transmission mated to a large, lazy V6 engine. 3.5, 3.9, just over 200 hp, four speed transmission. Most are geared to at least 40 mph / 1,000 rpm in top. Most show low consumption on the freeway...

Do these also have plenty of torque low down (thus the low output), or are they just inefficient?

Kostas

My engines on all my cars still generate a vacuum for the brakes when turned off as long as they're still spinning.

With the ignition switched off, the engine being turned over by the car driving forwards is a pretty decent brake in its own right...