+ and - of automatic gearbox - is manual better?

If you are cornering so fast on a public road that you are worried about losing it because of a gear change, then you are driving dangerously. There could be a pothole or diesel on the road. What are you going to do if you round the corner and there's a tree down, or a broken down car?

Most modern Autos *do* hold the car in lower gear till you hit the redline unless you ease off on the throttle. Likewise if you kick down the throttle from a standing start, they go like shit off a shovel.

The second-from top gear is almost always selectable with an 'OD off' button on the gearstick, so no ambiguity. If the gear box is hunting, there's something wrong with it.

Sounds like you've only driven some crappy US Slushmatic thing - try driving a car with a good auto gearbox, and you will be amazed.

Fair enough. Still, I would prefer to have a manual and do it right every time, rather than have to judge that this or that point is probably OK for fuel effecency.

In the car I was driving, you could floor the throtle at 0 mph and it would not spin the wheels, it would accelerate slowly at low revs until you built up a bit of speed. Once it got up to what would be the power band in 1st it would accelerate quite hard. What happens when you do this?

In a manual I can get the most acceleration at low speeds. If you can also do this in an auto then the one I was in was definatly broken.

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Newsgroups: uk.rec.cars.maintenance From: snipped-for-privacy@myself.com - Find messages by this author Date: 30 Nov 2005 05:44:38 -0800 Local: Wed, Nov 30 2005 1:44 pm Subject: Re: + and - of automatic gearbox - is manual better? Reply | Reply to Author | Forward | Print | Individual Message | Show original | Report Abuse

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Clive George wrote:

Not always. The most fuel efficent way to go from 0 to 60 (or whatever) if to keep the engine at 3 - 4k rpm at full throtle. You cannot do this in an auto (or not in the one I was in).

------------------ The last two autos I've owned did exactly that when you floored the throttle.

What did you do if you wanted full acceleration (ie. up to the red line at each gear change) then?

However big you want your saftey window, it needs to be bigger with an auto.

There could be a pothole or diesel on the road. What are

Avoid it or die. I would like as much control as possible when it happens.

I did try that. Did not decide it was the way to drive, I cannot remember why now.

I am sure you are right. I suspect there are more autos around that are like that than there are good ones, but ICBW.

- try

I can get a perfectly good car for 200 quid. You are sugesting I spend what, 15K (?) on a car that I cannot even choose the gear? ;)

Plant foot, engine spins up and car goes - all at the same time. Torque converter slips - engine is going a lot faster than if it wasn't slipping, so the engine's producing power all the time.

Sounds like it.

cheers, clive

5 speed autos came in around the start of the '90s and many are now 6, 7 or even 8 speed. Indeed, I was on a small LT bus the other day that had at least 6 speeds. ;-) These multi speed boxes only tend to use the torque convertor for start from rest and to cushion the gearchanges - it being locked out for most of the time - so have less of a fuel consumption penalty.

I think you're confusing efficiency with fuel economy. I may be *well* off the mark here, but I think an engine's peak efficiency means it's developing the most power per bit of fuel used. So that might be the best balance between quick acceleration, but as long as you're not labouring the engine, you're still better off using lower engine speeds - though like I say, not too low or you'll be labouring the engine. Obviously it's a lot slower, but it is using less fuel that way.

No it won't - you need to be more delicate with your right foot. You're hitting kickdown if it changes down at 4000 rpm.

If you want a faster step off from rest on an auto, you hold it stationary on the brakes with the left foot and rev up the engine a bit.

My bad. For some silly reason I read that as being about parking.. :-S

It enables you to steer whilst skidding. The best way to brake in the snow, or in any condition, is to not use enough braking force to cause the wheel to lose traction. So the best way to do an emergency stop is to brake as hard as you can without skidding.

As heavy as Porsche 911 clutches are supposed to be?

Try a BMW Steptronic, then. You move the entire lever over to the left which selects sports mode. Then if you move the lever forwards or backwards against a spring (like a motorcycle box) it goes into 'manual' and changes up or down and stays in that gear - provided you don't go beyond the preset upper or lower engine speeds when it will then either change up or down.

No it's not.

My understanding is that if you are going to accelerate to 60 anyway, you may as well do it at the engines peak efficiency, and then go into the highest gear you can to cruse. You are spending a bit more time at the inefficient high speeds, but getting there actually uses less fuel.

I could very easily be wrong though.

Maybe new ones do, but that doesn't mean most auto cars have a 5 speed box. I have a 99 Golf with only 4 and a 95 Mazda with only 4. The Mazda's top gear is about equivalent to 5th on a manual but the Golf's is not.

Anyway I could say that autos with an infinite number of gears came in long before the 90s ;-)

Z

I have finally found an efficency graph for my car [1]. I am correct that the engine is most efficent between 3k and 4k rpm. If there is a way to use the engine at lower efficeny yet get higher efficency you shall have to explain it as I cannot think how it is possible.

[1]

Going slower will do it, as the car requires less power to drive it along.

Ie it's not just engine efficiency which determines your total efficiency.

cheers, clive

Remeber efficency is energy out / energy in. Getting from a to b does not count as energy, so going slower does not improve efficency. I think if you are travelling at the same speed at the begining and end of your jorney your total efficency is 0? And I did say in a post above that I was assuming you are going to get to 60 anyway.

That's not a terribly useful definition of efficiency you're using. Energy, ie fuel, in for a given jorney or distance travelled is a more useful one here.

Even assuming you get to 60, doing it slower means you spend more time at the lower speeds, therefore you spend less energy shifting air around etc.

There are two conflicting things going on here : engine efficiency being improved by running at WOT, and power requirements being lessened by travelling slower. Both these are true, so determining which way to accelerate is more efficient (in my sense of the word) can't be done by merely considering one on its own.

cheers, clive