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  #1  
Old 09-30-2004, 09:51 PM
phita23 phita23 is offline
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Why Manual > Automatic?

Why, when all other conditions are identical, will a stick shift be faster than an automatic?
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  #2  
Old 09-30-2004, 09:58 PM
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An automatic transmission uses a torque convertor which is not as efficient as a clutch in transmitting power from the engine to the driving wheels.
  #3  
Old 09-30-2004, 10:37 PM
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  #4  
Old 10-01-2004, 12:44 AM
sbono13 sbono13 is offline
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Quote:
Originally Posted by phita23
Why, when all other conditions are identical, will a stick shift be faster than an automatic?
In addition to the inefficiency of the torque converter, the AT addes about 80 lb to the car's curb weight.
  #5  
Old 10-01-2004, 03:06 AM
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Quote:
Originally Posted by phita23
Why, when all other conditions are identical, will a stick shift be faster than an automatic?
A good drag-race driver has more control in a stick-shift car too, meaning he/she can launch the car more efficiently. The advantage basically comes from being able to control the engine (gas) and the transmission (clutch) independently.

Here's an interesting post that covers launch techniques for an MT car:
http://forums.bimmerforums.com/forum...ad.php?t=47538
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  #6  
Old 10-01-2004, 06:38 AM
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Something not mentioned also is the shift points.

Unless you have a steptronic tranny or similar where you can make the auto hold a gear, the auto will always shift into the next gear at some point. The next time you need to get on the gas, say coming out of a turn or passing, you have to wait for the auto to react to your input from the gas pedal. With a manual, you can select the gear you want ahead of time, therefor the power is there when you need it, not when the tranny thinks it is needed.
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  #7  
Old 10-01-2004, 06:43 AM
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In addition to what others have said, the gearing is almost always shorter in manual trans cars, when compared to the identical car with an automatic. Shorter gearing should equate to faster acceleration in most cases.

The main thing is control. Control over what gear your car is in at all times. Not such a big deal under normal/lazy acceleration, but a BIG deal when cornering.
  #8  
Old 10-01-2004, 07:22 AM
hector hector is offline
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Quote:
Originally Posted by Pete Teoh
An automatic transmission uses a torque convertor which is not as efficient as a clutch in transmitting power from the engine to the driving wheels.

agree about the efficiency issue but doesn't a torque converter also multiply torque?
  #9  
Old 10-01-2004, 08:06 AM
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norihaga norihaga is offline
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Quote:
Originally Posted by ff
In addition to what others have said, the gearing is almost always shorter in manual trans cars, when compared to the identical car with an automatic. Shorter gearing should equate to faster acceleration in most cases.

The main thing is control. Control over what gear your car is in at all times. Not such a big deal under normal/lazy acceleration, but a BIG deal when cornering.

Shorter, because you typically have less "gears" to do the same work, so they must be spaced further "apart". And then to get back some of the driveline losses the top gear is usually way overdriven, though I'm basing this on my crappy rental car experiences.

What happens to the gearing if you have the 7-speed Mercedes slushbox? I wonder...

But in any case, you still have the greater %age power loss from the driveline.
  #10  
Old 10-01-2004, 08:09 AM
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Quote:
Originally Posted by hector
agree about the efficiency issue but doesn't a torque converter also multiply torque?
No. The torque converter simply transmits torque from the engine flywheel to the planetary gearset within the transmission in a smooth, linear fashion. The gears themselves actually multiply torque, just like a gearset within a manual tranny. So to say that an automatic car with a torque convertor multiplies torque implies a manual transmission doesn't also do the same thing. They both do.
  #11  
Old 10-01-2004, 09:39 AM
Marco Marco is offline
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Quote:
Originally Posted by ff
The main thing is control. Control over what gear your car is in at all times. Not such a big deal under normal/lazy acceleration, but a BIG deal when cornering.
Absolutely!!!
I hated not being in control when I had an automatic and I am not particularly happy with the StepTr. I have now. Its delay in downshifting drives me crazy.
Fortunately I can have fun with my little FIAT.
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  #12  
Old 10-01-2004, 11:58 AM
st_o_p st_o_p is offline
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Didn't somebody mention that the auto tranny actually shifts faster than manual cause of the shorter differential?
  #13  
Old 10-01-2004, 12:07 PM
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Quote:
Originally Posted by ///M-Spec
No. The torque converter simply transmits torque from the engine flywheel to the planetary gearset within the transmission in a smooth, linear fashion. The gears themselves actually multiply torque, just like a gearset within a manual tranny. So to say that an automatic car with a torque convertor multiplies torque implies a manual transmission doesn't also do the same thing. They both do.
M-Spec, you`d better go back to Auto Trans 101 and brush up on your knowledge....a torque converter MOST DEFINITELY multiplies torque, usually by a factor of between 2 to 3 times. Here`s why a Step (or other auto) feels faster, at least initially....
Let`s take two non-ZHP 330is, one with manual, and one with Step: Torque is identical (214 lb./ft.) for both.
Manual- First gear= 4.35:1 Rear diff= 2.93
Step- First gear=3.45:1 Rear diff= 3.38

If you do the math (214x4.35x2.93), you will see that the manual trans model will give a maximum of 2727 lb./ft of torque (at maximum multiplication). Assuming the torque converter provides a multiplication factor of 2.5, and again, doing the math, (214x2.5x3.45x3.38) you will find that the result is a *staggering* 6238 lb./ft. of torque.
But it`s not all a free lunch....due to fluid & pumping losses there`s a loss of efficiency that eats up some horsepower, and by about 70 mph, the torque converter loses all advantage over it`s stick counterpart.

For proof of this, next time your car is in for service, and they give you the ubiquitous 325i w/Step, try the following (on a deserted road, of course): hold down the DSC button `til the yellow "BRAKE" light comes on....*stomp* the brake pedal with your left foot, and bring the revs up to about 2000 or so, let off the brake, and FLOOR that sumbitch....you`ll swear you`re at Raceway Park....

Regards,
Bob

Last edited by Fast Bob; 10-01-2004 at 12:12 PM.
  #14  
Old 10-01-2004, 12:13 PM
ff ff is offline
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Quote:
Originally Posted by st_o_p
Didn't somebody mention that the auto tranny actually shifts faster than manual cause of the shorter differential?

The problem is getting it to shift...
  #15  
Old 10-01-2004, 03:36 PM
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Quote:
Originally Posted by ff
The problem is getting it to shift...


By the time it acutally DECIDES to shift and then shifts, you could have shifted a manual and then been on your way.

The lag in the step kills me every time I get a loaner. Furstrating enough I just put it in drive and forget about trying to select my own gears until I am back in my own car.
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  #16  
Old 10-01-2004, 03:55 PM
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remington remington is offline
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I hate manuals. The average driver would be faster in the steptronic in auto-sport mode than in a manual. Eventually the advantages of a manual BMW will disappear even for skilled drivers as racing technology continues to trickle down to production model auto trannys. Seen a manual F1 lately?
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  #17  
Old 10-01-2004, 04:08 PM
LeucX3 LeucX3 is offline
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Quote:
Originally Posted by remington
I hate manuals. The average driver would be faster in the steptronic in auto-sport mode than in a manual. Eventually the advantages of a manual BMW will disappear even for skilled drivers as racing technology continues to trickle down to production model auto trannys. Seen a manual F1 lately?
Perhaps, but the fun factor and a sense of control will always warrant a manual tranny for some of us.
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  #18  
Old 10-01-2004, 04:58 PM
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Quote:
Originally Posted by LeucX3
Perhaps, but the fun factor and a sense of control will always warrant a manual tranny for some of us.
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  #19  
Old 10-01-2004, 07:53 PM
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IMHO manual gear boxes create safer drivers that are more alert.

I got a minivan for a loaner at my last service (thanks DiFeo ) and after a few minutes of getting used to not finding a clutch, I tended to zone out and not pay as much attention to the road. I picked up my cell and started jabbing away while I scarfed down a big mac and fries (J/K ) After a few minutes I wondered who stopped at the last couple stop signs.

With a 5 speed you have to look ahead and most of all anticipate- cross walks, hills, merging traffic, other stupid ass drivers that are capable of anything.

But then again I tend to drive faster and more 'spirited' in my 5 speed especially when I aim for that perfect double clutch heel-toe into a corner

Are manual drivers safer?
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  #20  
Old 10-01-2004, 08:24 PM
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i absolutely agree with shizat63, with a manual you HAVE to be more involved in your driving. with an auto, you just zone out and barely steer.

and if you're gonna get an auto, why bother with a bmw? why not just get an accord for chrissakes?
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  #21  
Old 10-02-2004, 03:23 AM
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Quote:
Originally Posted by Fast Bob
If you do the math (214x4.35x2.93), you will see that the manual trans model will give a maximum of 2727 lb./ft of torque (at maximum multiplication). Assuming the torque converter provides a multiplication factor of 2.5, and again, doing the math, (214x2.5x3.45x3.38) you will find that the result is a *staggering* 6238 lb./ft. of torque.
But it`s not all a free lunch....due to fluid & pumping losses there`s a loss of efficiency that eats up some horsepower, and by about 70 mph, the torque converter loses all advantage over it`s stick counterpart.
The caveat about a torque converter's multiplication effect is that it is only there when the engine is spinning much faster than the transmission (standing on the brake pedal and bringing the revs up close to stall as you describe).

The torque converter can lose its advantage before 70 mph, basically when the transmission speed approaches the engine speed and the stator starts to free-wheel.
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  #22  
Old 10-02-2004, 07:32 AM
hector hector is offline
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[QUOTE=FenPhen]The caveat about a torque converter's multiplication effect is that it is only there when the engine is spinning much faster than the transmission (standing on the brake pedal and bringing the revs up close to stall as you describe).

The torque converter can lose its advantage before 70 mph, basically when the transmission speed approaches the engine speed and the stator starts to free-wheel.[/QU


given what you and fast bob have described, overall in daily driving would you say that one would be experiencing significant torque multiplication or is it reallly just a 1st gear brake-torqueing dragstrip phenomenon?
  #23  
Old 10-02-2004, 08:09 AM
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Quote:
Originally Posted by phita23
Why Manual > Automatic?
Simple, the answer is: Less people you know will ask to drive or borrow your car.
  #24  
Old 10-02-2004, 08:53 AM
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[QUOTE=hector]
Quote:
Originally Posted by FenPhen
The caveat about a torque converter's multiplication effect is that it is only there when the engine is spinning much faster than the transmission (standing on the brake pedal and bringing the revs up close to stall as you describe).

The torque converter can lose its advantage before 70 mph, basically when the transmission speed approaches the engine speed and the stator starts to free-wheel.[/QU


given what you and fast bob have described, overall in daily driving would you say that one would be experiencing significant torque multiplication or is it reallly just a 1st gear brake-torqueing dragstrip phenomenon?
In "normal" everyday driving, most converter advantage will be realized with a relatively agressive throttle opening in first & second gear....the higher the RPMs, the more multiplication effect you get. Some American manufacturers give their cars a very agressive (*twitchy*) gas pedal to give the impression that the car is fast.

Regards,
Bob
  #25  
Old 10-02-2004, 09:12 AM
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Quote:
Originally Posted by hector
given what you and fast bob have described, overall in daily driving would you say that one would be experiencing significant torque multiplication or is it reallly just a 1st gear brake-torqueing dragstrip phenomenon?
Basically at low revs you will get a torque multiplication effect similar to a lower gear until the fluid stops shearing between the rotor and stator, this gives the "disconnected" feeling of an automatic transmission, it has two side-effects - a continuously variable gear ratio within a small range and a buffering effect that cushions the driveline. Once the stator and rotor spin at the same speed, there is no torque multiplication.

Really the torque multiplication of the torque converter has limited practical use, if you try to use this effect for increasing the vehicle performance you can easily overheat the transmission (torque braking for more than a couple of seconds can easily do this as you are dissipating the engine power by shearing the transmission fluid and converting most of the power into heat).
 

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