How Many Gears In A Transmission Is Too Many?

nicholastanguma

Los Angeles, San Francisco
Baker Drivetrain has been offering a 7 spd direct-drive tran for Harley Davidsons for a few years now, and aftermarket specialists like Mendeola and Quaife offer 6 and 7 spd direct-drive transmissions and transaxles for the automotive sector. Got me to wondering why OEM manufacturers don't do something similar? I know way back in the day Honda had some of their small displacement thumpers (100-200cc) equipped with 8 spd gearboxes.

I'm really quite obsessed with old small displacement pushrod engines, but often not with their accompanying gearboxes. Doesn't a torquey small displacement engine matched to a 7 or 8 spd direct-drive transmission seem like vintage overlanding paradise, or am I missing something?
 

NMC_EXP

Explorer
Spicer made a 20 speed transmission for semi-tractors. It was a 5 speed main with an air shift 4 speed auxillary.

Brown-Lipe made auxillary gearboxes that were used in smaller vehicles. Some had overdrive and could be used to split shift the main transmission. Commonly referred to as "Brownie boxes".

The auto manufacturers are adding gear ranges to get better performance out of the ever smaller displacement engines demanded by CAFE fatwas.
 

(none)

Adventurer
Guess it depends on what it is in and manual vs automatic.

Automatics make it much easier to add quite a few gears, they can be programmed to skip gears, start in 2nd or 3rd, etc. When Porsche came out with the Cayenne with the 6-speed auto, they would start in 2nd gear unless you stomped on the throttle, then it'd drop to first. Kind of like the granny gears on older pickups. Had an Audi A4 with the 8-speed trans. I was happily surprised how well it shifted without feeling too much like it was always finding another gear. I'd be interested in checking out the 10-speed in the F150.

Manual for most cars and trucks, I think the 5-7 range is good. It all depends on the spacing. The JKs I had all had manuals (6-speeds). The 6th was just barely taller than 5th. Downshifting from 6th to 5th did nothing, always had to at least hit 4th. The gears could've been spaced better to keep the 6th or just eliminate it and go back to the 4th. I know the Porsche and Corvette 7speeds keep that big OD gear which I can see being nice for highway cruising.
 

javajoe79

Fabricator
As many as you need to stay in the torque for any given engine. I've driven a few newer autos with 6+ gears and it makes a difference. It's faster or more efficient as needed.
 

Happy Joe

Apprentice Geezer
Depends on the use, IMO...
10 speeds is likely enough for most semi-truck tractors.
5, high range, speeds is (in my experience) plenty for most properly set up, reasonable, dual purpose DD/off road vehicles.
...special purpose vehicles have differing requirements.. and every driver can be expected to have different preferences.

Enjoy!
 

Herbie

Rendezvous Conspirator
As (none) says, it's all in the spacing.

On the road, we're a BMW family, having owned nearly a dozen between my parents and my wife and I. For most of those, a 5-speed manual and a 4- or 5-speed auto was plenty. In particular, the wife's E46 325i with the M54B25 engine and 5-speed auto is simply amazing - so good, in fact, it tricked me into buying a car I don't love*. Likewise, I had a E36/8 Z3 coupe with the M54B30 and a 5-speed Getrag manual that was so well setup that it effortlessly transitioned from sports car to GT cruiser. I loved that car.

Then, however, came drive-by-wire throttles and extra gears, mostly in an attempt to eek out some better fuel efficiency. *My E91 wagon with the N52B30 is a powerful enough engine (a bit more power and torque than the older engine in my Z3 coupe), but the damned 6-speed auto transmission is horrid. Unless I drive it in manual mode (I have the M-sport with the flappy-paddles), it ALWAYS seems to be in the wrong gear. The problem with driving it in manual mode is that it also changes the throttle response and other settings, so it's hard to have a relaxed, smooth drive. It either wants to lollygag in the wrong gear, or race around getting speeding tickets. (The manual-trans versions are rare-as-hen's-teeth in the wagons, but I've driven a couple and they're much better, but not perfect - again down to gear spacing.)

By comparison, just a couple year's later the F30 3-series cars got the 8-speed auto, and now they're back to being smooth and responsive. The gear spacing and programming is such that you never feel like you're waiting for it to kick-down as you try to accelerate out of a corner, etc.
 
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eggman918

Adventurer
In my '68 F-250 that weighs 8,000 with a full fuel tank and the relatively small displacement 3.8L 4BT the ZF-5/ NP-203 underdrive Is a great combination IMO.
With the ZF in direct the 4BT is is happy and moves the truck well when backing and on trails the 2-1 under is a good match and saves a lot of wear and tear on the clutch, we also toe a short 3,5003 camp trailer off road a lot and the under drive makes that much easier. In direct the speed range is up to 80 keeping the engine in its sweet spot and in under 40-45 is tops which suites nearly all trail conditions except the truly difficult ones, but I have the T case low range for that which with the underdrive gives me 3.96-1 but in all honestly that has been used just a handful of times and then only with the trailer and mainly to lessen the workload on the clutch......$.02
 

rcab87

New member
If you look around in the current automotive market, there are many vehicles with 8+ speed transmissions. The Silverados and Sierras with the 6.2 come with an 8 speed auto, and the new F-150 Raptor and Camaro ZL1 come with a joint Ford-GM developed 10 speed automatic.
 

Metcalf

Expedition Leader
The broad gearing in modern 6+ speed automatics can be amazing. No more need to do the high-low shuffle on mild sections of trail. My new Land Cruiser project has a 54:1 crawl ratio in low range, but can still do 6'5mph in low before 5000rpm. This should be great for the sand, desert, and mild sections of deep snow....

I'd love to play with the new GM 8spd automatic next. That thing has even broader gearing....
 

Xbcasey

Adventurer
The more gears the better. An engine only has one specific rpm where it is running at peak efficiency/power for the situation, the closer it can stay to that number, the better. The only way to stay close to that number, is with a lot of gears, or even better, a computer controlled CVT. I'm amazed that more auto manufacturers haven't gone to computer controlled CVT, they are absolutely the way to go.

A few people have mentioned truck transmissions, they show the difference even more clearly. A lot of people are getting away from manual transmissions in trucks and going to automatics for that very reason and have been getting amazing results. The Allison automatics are blowing away every manual transmission out there in big trucks.

I work in heavy haul and move up to around 250k loads, my truck dyno's 741hp to the ground, has an 18 speed transmission, a 4 speed auxiliary transmission, and 2 speed rear ends, that's 144 possible forward gear combinations. Now there's no way to use all of them in a row, but I have an option for pretty much any situation. Even with all that, our new truck with a 600hp engine (that should be 500ish to the ground) and an Allison 6 speed automatic absolutely blows mine away in every category. It gets 1mpg better fuel mileage, 50% longer drive tire life, a drastic reduction in drivetrain maintenance costs, and with an even load on both trucks, it absolutely blows mine away despite having about 240 less horsepower.

The 1 mpg might not sound like much, but it's actually a 20% increase in mileage, which saves us about $8k a year in fuel costs A full set of drive tires cost about $8k a set and at a set per year that's another $4k savings. As far as drivetrain maintenance, we are seeing absolutely no wear in the carrier bearings, U joints, power divider, or pinions, the diffs themselves also run noticeably different. My truck on the other hand is already due for new U joints and carrier bearings even though they were changed at about the same time as we got the truck with the automatic, that's another thousand in maintenance costs, plus half a day of down time.

So the automatic saves us between 12 and 15 thousand dollars a year right off the bat, and outruns trucks with far more horsepower. The reason for pretty much all of this is that the Allison automatic never lets off the throttle to shift. It grabs the next year under full power and never leaves the drivetrain coasting while it changes gears. It also uses its torque converter to mimick more gears in between the 6 that it has. Instead of jumping straight from one gear to the next, it slowly ramps up the ratio until the next gear is fully engaged. The manual transmissions, and the Eaton automatics, which are an automatically shifted manual transmission, have to let off the throttle, allowing the truck to coast and lose momentum, grab the next gear, then power back into the throttle to accelerate again. It is quite literally two steps forward and one step back and wastes a huge amount of energy.

There has been quite a bit of talk of going to a CVT transmission for trucks, which I think would be great. It makes nothing but good sense to put the engine at its peak power/efficiency rpm (which varies with the load placed on it) and let it already stay at that number while the power is put smoothly, evenly, and uninterrupted to the ground.

So to answer the question of how many gears is enough?? Infinity is my answer. There isn't enough gears out there to let an engine truly work correctly.

Sent from my XT1650 using Tapatalk
 

javajoe79

Fabricator
I agree on the CVT potential. Seemingly they can't take much power but you would think a scaled up version would be fine.
 

dwh

Tail-End Charlie
I remember reading an article in a motorcycle magazine 30-40 years ago. They interviewed a guy who raced (IIRC) flat track. The one thing he said that I've never forgotten was,

"The only reason anyone ever made a transmission, is because they couldn't make a good enough engine."


The CVT is a way to make a piston engine have characteristics more like an electric motor. The professor who invented the lithium ion battery recently also helped invent a glass electrolyte battery. Not long ago, the carbon-carbon battery was invented in Japan. The new battery technologies are major game changers. I, for one, will be very happy to use electric motors for propulsion and leave the internal combustion for making electricity.



I work part-time for Penske ferrying tractors and trailers around to different locations, so I drive Freightliners, Volvos, Internationals, Kenworths and the occasional Peterbuilt. Also ferry MDTs of various sizes and brands.

And yea, the Eaton automatics are terrible. Not only do they let off the throttle to shift, they don't skip gears. In traffic the constant on and off the throttle upshifting/downshifting drives me nuts. One guy said he had to to pull over - he started feeling seasick. Mostly with the Eatons I just switch it to manual mode and control the shifting myself. Even so, I'd rather have a manual over the Eaton so I could skip gears when I want.

But the Allisons are great. Did a long run in a brand new Freightliner Cascadia sleeper cab last night. It was like driving a Cadillac. Well, except for the high winds blowing the thing all over the road. (Going to be interesting to see how auto-pilots are supposed to deal with that.)



Public Service Announcement: In high wind conditions, do not be a bloody fool and drive along right next to a big rig.

(Some ************ did that to me last night. For miles. I slowed down, he slowed down. I sped up, he sped up. Idiot.)
 

broncobowsher

Adventurer
In the 80's you could get an 8-speed manual in a Dodge Colt. It was a 4-speed with a splitter. Had a friend who had one and out of bordom you can drive it as an 8-speed.
The 80's Honda 3-wheeler was a 10 speed(?) 5 gears with a high/low range.
Even C4 vettes had a 7-speed before the 5-speed came out. It was a 4-speed transmission with an overdrive that could be switched on in 2-4th gear.
That is just normal stuff that is pretty old.

Today the modern automatic transmissions have plenty of gears. 10 speed is available in several vehicles now. Spacing and timing are needed to make them work right. The ZF 8-speed is pretty amazing. I read a paper on it once and am impressed how simple it really is. If you think of the early automatic overdrives they ran 3 planetary sets, 6 or more frictions, at least 2 sprags. The ZF adds one planetary set, so 4 sets of gears. But has no sprags and only 5 clutches. And any forward gear has 3 clutches locked up, so only 2 are creating drag. That is pretty freaking amazing. Now it does take a decent computer to run all this, but those are common these days.
 

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