Why do autos seem to rev higher than vehicles with manual gear boxes?
On my lunchbreak a BMW X1 passed me - the driver was probably doing no more than 15mph - I think he was looking for an address, but the engine seemed to be revving quite high relative to his speed. Would this high revving be the reason autos are less economical then a manual gearbox?
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No. An automatic is drawing energy from the engine into the torque converter even when the car is not moving, and there's built-in slip at moderate speeds too. It helps with the impression of smoothness but comes at a price in energy efficiency.
Most automatics can be locked in a low gear or range of gears, and this may have been what you heard. An elderly neighbour used to drive past my old house with her (presumably manual) Seicento permanently in first. She could be heard from streets away.
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I lived (in the country) next to someone who would start his car from cold in the winter and within 3 seconds rev it to max and hold it there (steady revs) until the temp guage was in the middle.
He reckoned that it was bad to drive a cold engine, so he warmed it as quickly as he could!
Last edited by: Tigger on Mon 20 May 13 at 14:06
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>> I lived (in the country) next to someone who would start his car from cold
>> in the winter and within 3 seconds rev it to max and hold it there
>> (steady revs) until the temp guage was in the middle.
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>> He reckoned that it was bad to drive a cold engine, so he warmed it
>> as quickly as he could!
>>
There was a Greek bloke who lived opposite my old Maths tutor who did that. He'd been told to allow his new Merc to warm up before driving off. He'd sit on his drive with the throttle wide open and with flames belching from the exhausts.
Very funny and I wonder to this day how long that thing lasted.
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A Continuously Variable Transmission (CVT) works differently - usually setting one of two priorities, economy or performance. Having decided this it then matches the engine speeds and gear ratios in a mix which it calculates is the best one to achieve it.
My car has a CVT gearbox. I can drive in a quiet, relaxed manner at well under 2000 revs and still find that I am going just a bit too fast to be legal (if I am not careful).
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There is a school of thought that most drivers of manual cars drive in too high a gear, especially in built up areas.
www.rospa.com/roadsafety/adviceandinformation/driving/speed/toptentips/third-gear.aspx
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>> There is a school of thought that most drivers of manual cars drive in too
>> high a gear, ................
Too high a gear from what viewpoint? Not from the fuel economy or emissions viewpoint.
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>> Too high a gear from what viewpoint? Not from the fuel economy or emissions viewpoint.
From viewpoint that in a lower gear the engine note's rise and fall provides an aural clue as to speed - helps maintain 20 or 30.
Third for 30 and second for anything less - eg 25 or lower past the school - works fine in both our (diesel) cars.
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>> Third for 30 and second for anything less - eg 25 or lower past the
>> school - works fine in both our (diesel) cars.
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In my manual petrol car, 25 mph in second gear is 2600 RPM. That's too much for me to tolerate at a constant speed.
Last edited by: L'escargot on Mon 20 May 13 at 18:46
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>> There is a school of thought that most drivers of manual cars drive in too
>> high a gear, especially in built up areas.
If I drive the 320d in 'ECO PRO' mode, it starts nagging me to change up if I am over 1500 RPM in any gear, except 6th of course.
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Most autos, tuned for maximum economy seem to try and stiff you in too high a gear as soon as possible, leaving you with revs too low unless you "hold" it or kick (paddle) it down.
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As autos are not allowed to stall, the ECU sometimes pushes up the RPM to deliver enough torque. Having said so, most modern autos don't really over rev more than necessary.
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Automated manuals often select too low a gear at junctions etc (not their best area) leading to higher revs than needed and another immediate upchange, but normal autos keep the revs fairly low unless full throttle or kickdown is applied.
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I often think that my Saab is capable of pulling a higher gear at a given speed than the auto box allows it to. It's no good putting in manual mode, because if you do it just overrides the selected gear if it thinks it is too low. IIRC it doesn't get into 5th until 40mph, and is quick to drop to 4th.
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I have a Jazz CVT with 7 gears. If I drive in D it will change up under 2,000rpm as long as I do not accelerate hard. IF I use S, 3,000 rpm.
Too hard a push on the throttle by a could not care less driver means any auto will be in a lower gear and revs higher than they could be.
At 70mph, I can drive with a gentle foot in 7th and get 57mpg. Or drive harder in 6th and get 54mpg and go no faster...
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>>I have a Jazz CVT with 7 gears
A neighbour got very annoyed when I told him it hadn't got that many gears, but just pseudo gears. I then compared his gearbox to an automated moped.......................
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Does your gearbox have a Continuously Variable mode, madf?
The reason I ask is that I vaguely remember reading about a Nissan gearbox which was technically a CVT but which just used fixed ratios. (This may have been in the USA). I think that they fitted a CVT-type box to save space and weight, and because customers found the characteristics of the CVT a bit off-putting.
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but surely, if it has fixed ratios its not a CVT?
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>>but surely, if it has fixed ratios its not a CVT?
You are correct. It was an unusual setup, to be sure. I think they only fitted it as a short-term measure because they got a lot of bad feedback from Americans who were used to conventional automatics.
IIRC it used only fixed ratios for "drive" and "sport". It didn't operate in CVT mode at all. By comparison, the gearbox in my current car operates in CVT-mode when in (D)rive, and uses 8 fixed gear ratios in (S)port.
ASIDE:
My Primera petrol automatic from 1997 (lovely car) had a CVT transmission with a torque converter (instead of a clutch pack like my current car)
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It has 7 fixed ratios in D but only 5 in S - appears to lose gears 6&7 or is it only 7? (Dunno) but I believe it involves CVT technology to get there.. Plus a torque convertor, The change - even under power - is very smooth.
Not to be confused with pre 2012 CVTs on Jazzes - either I shift - automated change - or CVT with dog clutches (which wear).
I drove an A4 Multitronic c 2006 and it was err horrible...
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On my diesel auto if I leave it in "E" ( which I think stands for E-conomy ) it changes up at about 1500-2000 revs which is probably about where I would anyway on a diesel manual. If you put it in "S" ( which I think is S-port) it hangs on to the revs a bit longer.
It does feel quicker in "S" but I'm not sure if it is or whether it just sounds like you're going faster.
If I really want to get on with it I put it in "M" and either tip it with the gearlever or use the flappy paddles.
Most of the time though I just leave it in "E" and listen to the radio.
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>> drove an A4 Multitronic c 2006 and it was err horrible...
It was, and it had a poor reliability record. Audi used it's customers as guinea pigs and made them pay the cost. The revised multitronic from 2007 is much better.
You still can't beat a proper automatic, though! ;-)
Last edited by: Londoner on Mon 20 May 13 at 19:04
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Referring to madf's post,I had a Mk1 CVT. Start clutch problems cause juddering when pulling away from rest.Initially Dealers charged up to £400 to flush the gearbox and others £1000+ to replace the start clutch.
Honda then increased the warranty on the box to 7 years or 100K.
I had a free flush and a new type of fluid about 2 1/2 years ago but about a month before it was 7 years old the judder re-appeared.
The Dealer said Honda required them to do a flush and check it after 200 miles.
At that point mine was fine, so I reasoned that I would be paying for a new start clutch myself fairly soon, so I traded it in for an i-Shift.
I have no issues with AMTs-I have a Smart Roadster and a Fiat Comfortmatic Camper van-both with AMTs.
The CVTs MK1 & Mk2 operate seamlessly in D, and have 7 "artificial" gears in Manual mode.
Interestingly,in the i-Shift, if you leave it in manual it changes down as you slow up, and will change up when the revs hit 6k.
I also found with my CVT that if you accelerated away at about 2000revs it was quiet and raised the gear as speed increased.
I realise how some posters hate AMTs, but Honda recently recalled i-Shifts for a problem with the gear selector if it was repeatedly parked on hills in R.
Since the recall mine is a lot smoother and even does "mini" double-declutches when changing down going up hills.
It's still far better than pumping a clutch and stirring a gear lever!
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well I have an automatic 4x4 and it very rarely goes over 2300RPM
mostly changes gear at about 1700 rpm so have no idea where you get the idea that auto's rev their socks off ! mostly a driver issue. If i kick mine down when overtaking it may go to 2700 rpm tops before it changes and when its cruising at 70 mph its doing about 1600 rpm
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>> Why do autos seem to rev higher than vehicles with manual gear boxes?
>> On my lunchbreak a BMW X1 passed me - the driver was probably doing no
>> more than 15mph - I think he was looking for an address, but the engine
>> seemed to be revving quite high relative to his speed.
What makes you think it was an auto?
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>> What makes you think it was an auto?
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Good point, BP! The OP assumed that the car had an automatic gearbox and the rest of us kind of followed along.
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Most autos run at higher RPMs when the engine is cold, this is stated as being to reduce tailpipe emissions and warmup time in the owner's manuals.
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>> What makes you think it was an auto?
Well the noise it was making - there is a distinct difference in engine note and the way (and speed) at which an auto changes gear. Shortly after he passed me he sped up and I heard it change gear so it sounded very much like an auto to me.
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I LOVE the sound of a slurred gearchange with a torque convertor.
(Especially on a V8)
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>> I LOVE the sound of a slurred gearchange with a torque convertor.
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>> (Especially on a V8)
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Yes, I used to own a V8 Discovery. Marvellous burbling noise and effortless waft a mere shove of the loud pedal away.
I'd by another one, if I could work out how to get someone else to pay for the petrol. 4 litre housebricks are a tad thirsty.....
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Automatics and revs - WillDeBeest
