Bazillion speed auto trannies.

[MobilOne]

FWIW and IIRC, the 1955 and 56 Packards had a 4 speed auto with a lock up torque converter. 4th gear was OD behind a big V8. Also Studebaker in the '60s had a lock up converter.

[jcp123]

I don't recall the old 4-speed autos having OD, but there were always the BW units with overdrive back then. That's what I'd like in my Chevy Wagon project, should she ever come to fruition.

[serialk11r]

I can understand why 7 might be too much for a manual transmission, but how is it bad that an automatic has more gears?

A lot of you are mentioning "torque band", but that's totally missing the point. What we actually care about is efficiency band, not torque band, and more gears helps put you there faster. If a shift drops you from 2500 to 1600, the engine is quite a bit less efficient than if the transmission could keep the revs above 2000, during acceleration.

If you're going >50mph, then you're probably in the tallest gear, but what about 45? Or 35? Or 40? If at 40mph you have to shift into 5th gear in a 6 speed, that could mean running the engine 60% faster with wide spacing, and losing 20% fuel economy. An 8 speed avoids that by having 2 gears closer together in that range.

More speeds also lets you bring 1st gear lower, reducing torque converter losses, or in the case of a DCT, less heat at the clutch.

I'm also not convinced there isn't a workaround for 7 speed M/Ts. Aston Martin's new V12 Vantage S M/T has a dogleg pattern with 1st gear under reverse, to the left. I imagine 1st and reverse would be blocked once you get rolling, and then you use 2-7 in the usual H pattern. That sounds workable to me. Porsche blocks 7th gear if you are in 4th or lower, which is probably not as good since if you're in 7th and trying to downshift, finding the right gear is going to be way harder.

Finally, all that said, I'm kind of surprised to see 9 and 10 speed automatics showing up on the market. I mean, maybe on a 7L Lamborghini, which can hit the rev limit in 7th gear, but 8 seems like it would be more than enough for most cars...I suppose 9 speeds gives you a lower 0-60 time for bragging rights, since most cars space 1st and 2nd further apart.

[Baltothewolf]

I think anything more than 4 gears in an auto is silly. Want taller gearing? CVT.

[pete c]

Originally Posted by serialk11r

I can understand why 7 might be too much for a manual transmission, but how is it bad that an automatic has more gears?

A lot of you are mentioning "torque band", but that's totally missing the point. What we actually care about is efficiency band, not torque band, and more gears helps put you there faster. If a shift drops you from 2500 to 1600, the engine is quite a bit less efficient than if the transmission could keep the revs above 2000, during acceleration.

If you're going >50mph, then you're probably in the tallest gear, but what about 45? Or 35? Or 40? If at 40mph you have to shift into 5th gear in a 6 speed, that could mean running the engine 60% faster with wide spacing, and losing 20% fuel economy. An 8 speed avoids that by having 2 gears closer together in that range.

More speeds also lets you bring 1st gear lower, reducing torque converter losses, or in the case of a DCT, less heat at the clutch.

I'm also not convinced there isn't a workaround for 7 speed M/Ts. Aston Martin's new V12 Vantage S M/T has a dogleg pattern with 1st gear under reverse, to the left. I imagine 1st and reverse would be blocked once you get rolling, and then you use 2-7 in the usual H pattern. That sounds workable to me. Porsche blocks 7th gear if you are in 4th or lower, which is probably not as good since if you're in 7th and trying to downshift, finding the right gear is going to be way harder.

Finally, all that said, I'm kind of surprised to see 9 and 10 speed automatics showing up on the market. I mean, maybe on a 7L Lamborghini, which can hit the rev limit in 7th gear, but 8 seems like it would be more than enough for most cars...I suppose 9 speeds gives you a lower 0-60 time for bragging rights, since most cars space 1st and 2nd further apart.

It's not that it is bad. I just question the benefit for the added cost, complexity and weight.

[pete c]

Originally Posted by Baltothewolf

I think anything more than 4 gears in an auto is silly. Want taller gearing? CVT.

Going beyond 4 is definitely not silly. Having 5 and even 6 gears allows you to have a stump puller 1st and a nice high cruising OD gear without having huge gaps between gears. For some vehicles, I believe there is even a benefit from having 7.

8?

Questionable.

9?

Now you're just showing off, IMHO.

CVTs have certainly improved, but I still can't get used to that horrible drone. I will admit though, that the Sentra I rented last year would give 40 mpg without even trying.

[Baltothewolf]

Originally Posted by pete c

Going beyond 4 is definitely not silly. Having 5 and even 6 gears allows you to have a stump puller 1st and a nice high cruising OD gear without having huge gaps between gears. For some vehicles, I believe there is even a benefit from having 7.

8?

Questionable.

9?

Now you're just showing off, IMHO.

CVTs have certainly improved, but I still can't get used to that horrible drone. I will admit though, that the Sentra I rented last year would give 40 mpg without even trying.

My civic has no drone to it. I do know what you are talking about, the CVT insight has it bad.

[pete c]

Originally Posted by jcp123

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.

Added gear counts=more weight/complexity

This is a simple indisputable fact. For a 7 speed to be the same weight as a 6 speed, the 7 speed must be built of less robust parts.

Also, someone mentioned earlier that all that stuff is always spinning, meaning that the parasitic losses of a tranny would increase as you increase the number of bits inside that are spinning.

[spacemanspif]

Originally Posted by Baltothewolf

I think anything more than 4 gears in an auto is silly. Want taller gearing? CVT.

CVT is still governed by the size of the 2 pulleys. If the trans is designed for a 0.75:1 as tallest gear, you're in no better shape than typical 3spd/OD trans from the 80s. If the trans is designed with tallest gear if 0.25:1; well the the computer can pick the most optimal cruising gear.

[Frank Lee]

Originally Posted by serialk11r

A lot of you are mentioning "torque band", but that's totally missing the point. What we actually care about is efficiency band, not torque band, and more gears helps put you there faster. If a shift drops you from 2500 to 1600, the engine is quite a bit less efficient than if the transmission could keep the revs above 2000, during acceleration.

If you're going >50mph, then you're probably in the tallest gear, but what about 45? Or 35? Or 40? If at 40mph you have to shift into 5th gear in a 6 speed, that could mean running the engine 60% faster with wide spacing, and losing 20% fuel economy. An 8 speed avoids that by having 2 gears closer together in that range.

Just go fast enough to pull top gear. Done.

Engines having broad flat torque curves thus having a larger useful rpm range + vast multitudes of ratios is missing the point?

Efficiency band while accelerating? And accelerating lasts how long- a few seconds. Cruising along lasts how long- exponentially longer- could be hours. Put that thing in the efficiency zone when at cruise speed.