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Old 04-17-2016, 09:54 AM   #1 (permalink)
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Bazillion speed auto trannies.

Recently, I rented one of those Fiat SUV things. Looks like a Fiat 500 that got overinflated. It was a nice little rig and it has a 9 speed tranny.

I don't have any problems with that and it sure as hell beats an old 3 speed, but at what point does gear count become driven by marketing rather than engineers?

I think 9 is about a gear or two into that territory. I am currently renting a Kia Soul with a 6 speed and I think that is about right. 6th gear at 75 mph cruising speed is around 2700 rpm. And it is in 6th by 45 mph, assuming a light throttle. The Fiat, I noticed didn't get to 9th until somewhere around 70 and even looking at the throttle caused a downshift.

More gears means more weight and more complexity. Also, a tranny that is in the middle of a shift is less efficient than one in gear, so I think that it might actually mean a miniscule drop in efficiency. I would think that an 8 speed with the same final ratio would be just as efficient with an immeasurable loss in performance.

Another example of this is the new Vette with the 7 speed stick. That motor pulls like a freight train over almost all of its range. I have read reviews of it and they say that it doesn't shift as well as the 6 speed, which makes sense, because now you have 4 rows of gears rather than 3. One of the reviewers said it needed a 7 speed like it needed square wheels.

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Old 04-17-2016, 10:16 AM   #2 (permalink)
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If they put a tall final drive in for max highway mpg I can understand extra gears so that it's got a granny gear 1st to get out of the hole and still has something like 0.75:1 overdrive without 2000rpm drop between shifts. But it seems most cars are doing more shifting for the sake if doing more shifting with 300rpm drop gear shifts. I get that tighter gears can keep you in the power band better but I think 1000rpm drop is a good gear spacing especially since DI and VVT can make such broad power bands. Anything more than 6 and it better be an auto or a "flappy paddle shifter" becuase I'm way too lazy to coutch 8 times before I get to 45mph...that's for the big rigs.

To old mech's point, my friends Subaru XV has a CVT but programmed shift points. I wonder if the million speed autos are actually CVT but they are not calling them that becuase if the bad reputation they have for durability...
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Old 04-17-2016, 10:37 AM   #3 (permalink)
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It actually has an infinite lack of appropriate gears, so 9 is less of a compromise than 6, or 5, or 3.

I don't know why reviewers and other so-called car enthusiasts dislike it when their car seeks optimal gearing for the task at hand.
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Old 04-17-2016, 11:45 AM   #4 (permalink)
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Because effort and overall efficiency.

I prefer manual transmissions but that doesn't mean I want to shift 11 times to get to cruising speed. Even with five-speeds I skip-shift.

More gears = more gear meshes = more parasitic transmission losses. And weight. And expense.

I'd likely feel differently about it in the mountains, or if I was Type A behind the wheel and wanted maximum accelerative or pulling/towing effort from every start, but here in the flatlands a three-speed manual with direct drive third and a tall final drive would be the most efficient set-up.

Ironic this trend is happening now, when ICEs should have broader, flatter torque curves than ever before thanks in large part to variable valve timing.

P.S. Had opportunity to compare and contrast '13 and '94 F150s with a/ts; there's so much shifting going on in the '13 I have to look at the indicator lights to see what gear it's in and what it's doing.
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Old 04-17-2016, 03:01 PM   #5 (permalink)
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Bring back the Powerglide or the Dynaflow?
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Old 04-17-2016, 03:34 PM   #6 (permalink)
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'59 Bel Air and '66 Corvair both have 'Glides. '76 Camper Special has TH400. All they need are locking converters FTW.
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Old 04-17-2016, 06:55 PM   #7 (permalink)
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'59 Bel Air and '66 Corvair both have 'Glides. '76 Camper Special has TH400. All they need are locking converters FTW.
Truth but I like OD so I can run 3.73 rear and have acceptable highway rpm.
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Old 04-17-2016, 09:10 PM   #8 (permalink)
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Quote:
Originally Posted by pete c View Post
More gears means more weight and more complexity.

https://en.wikipedia.org/wiki/ZF_9HP_transmission

"The 9HP is only 0.24 inches (6mm) longer than, and weighs 16.5 lbs (7.5 kg) less than, the outgoing six-speed transmission."

I'm pretty impressed with the ratios available on that transmission. I would say 2, 3 or 4, 5, and 7 are equivalent to most older 4-speed OD autos. 1 is an extra short creeper/launcher gear. Nice for 4x4's. 8 and 9 are extra tall. You guys always talk about how you wish you had that extra gear to get the rpm down on the highway. Well there it is.
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Old 04-17-2016, 09:39 PM   #9 (permalink)
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Well!

If that tech was applicable to fewer-ratio'd transmissions they should be lighter yet?

They seem to be suffering some teething problems.
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Old 04-17-2016, 10:12 PM   #10 (permalink)
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I myself have kinda wondered about this. 5- and 6-speed autos seem right for the task at hand - more than that and it does seem like there's a bit of busywork along with a lot of marketing. I am told that these designs are not really more heavy or complex but I do wonder on that count.

The 6-speed on my wife's Chrysler (I really need to update my info here, lol) seems to border on busy but works pretty well considering it's a nearly 4800lb vehicle with a 3.6l engine tugging it along, and according to the FCD it's been getting mid-high 17s on my wife's in-town drives, along with 30+ on the freeway.

I had good access to a smorgasbord of cars in the 2011 period and I was generally happy with the 6-speeds I had. CVTs seemed a bit more picky - smallish Nissans did well but the Quest felt as busy as anything around. The 5-speed auto in my Dad's Passat felt similarly competent.

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