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Let me preface this question with the fact that I know how automatic and manual transmission are different in their operation. My question is, however, why do they differ in their amount of gears and subsequently their gear ratios? I can understand the difference in ratios when the two have a different amount of gears which seems to be almost always. Even in a performance car like the Porsche 911 Carrera the manual is a six speed while the automatic/tiptronic (full manual capable) is a five speed. This is just something I've been pondering for a while and I'm sure there is a simple answer but I have been unable to find it.
 

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My guess would be money. It's cheaper to make a 4 speed auto. This is all speculation, though.
 

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Because they use completely different styles of altering gear ratios. A manual gearbox has individual gearsets for each ratio. An automatic uses a planetary gearset (or two), and uses the same kind of technology as an old three speed bicycle hub. Your final drive ratio in an auto depends on which part of the planetary gearset you imobilize relative to the input or output. Autos use hydraulics to apply "brakes" to the ring gears or the outer ring itself to change ratios. Theres actually no gear "change" at all, just a braking effect on some part of the planetary gear system. They do it this way because it makes sense from a 1950's perspective and since they've been around so long, they've figured out most of the bugs and fixed them so they are reasonably reliable. A very few are quite strong, but most are relatively fragile compared to their manual equivalents.

That is unless you are talking about SMG. SMG is the shiznitz, it's the best of both worlds, and IMHO, the way it should have been done all along...
 

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Discussion Starter · #5 ·
Originally posted by lo bux racer@Jul 31 2005, 04:34 PM
That is unless you are talking about SMG.  SMG is the shiznitz, it's the best of both worlds, and IMHO, the way it should have been done all along...
So you have no problem with the clutch pedal going away then? I think SMG could make for a resurgence in manual transmissions. I can say with 100% certainty that if that had been an option on the tC I would have paid for it had it been extra.


Edit: Thanks for the answer, Lance.
 

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There is the fact that the auto has a torque converter. While a manual has a clutch which is a 1-to-1 drive, the torque converter never is 1-to-1...thus the need for the torque converter lockup. Being a "fluid coupling" the converter itself acts like a lower gear ratio (hense the name torque converter)...that's why the gears are usually taller (numerically smaller) in an auto vs. manual in an equivalent car. Initially, when the engine speeds up, the engine side of the torque converter spins much faster than the trans side. As vehicle speed increases, the ratio of speed between the two approaches 1-to-1. Theoritically, this should allow for less gears...in reality though, vehicle weight, engine torque, power band, final drive ratio, etc. all play a hand into how many gears would be needed for the desired output.
 

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hey Yaj???where are you from???...I am also a hmoob Yaj from MN...
 

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Don't usually let complete strangers know where I'm from...but if I ever get a tC and meet up with some of you somewhere...maybe if I get the tC before these guys make the trek out to Atlanta I may hook up with down along the way.
 

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Originally posted by Plissken@Jul 31 2005, 10:52 AM
Let me preface this question with the fact that I know how automatic and manual transmission are different in their operation. My question is, however, why do they differ in their amount of gears and subsequently their gear ratios? I can understand the difference in ratios when the two have a different amount of gears which seems to be almost always. Even in a performance car like the Porsche 911 Carrera the manual is a six speed while the automatic/tiptronic (full manual capable) is a five speed. This is just something I've been pondering for a while and I'm sure there is a simple answer but I have been unable to find it.
I just made a helpfull spreadsheet regarding the gear ratios:
http://www.mpegbox.com/car/

You can see my Honda CRV vs the automatic version and how the RPM at different speeds stackup against a tC.

I'm new to the fourms and I don't have a tC yet, but I was wondering if they make a 6 speed transmission that you could drop into the TC or if you could change the ratios so that 5th gear turns less RPMs. You can customize so much other stuff, what about the transmission?

-Jeff
 
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