How many gears

[Boza]

Hey guys I saw an ad for the new jeep Cherokee and it says they have a 9spd auto. I have driven cars with 6spd autos and thought geez they change gears a bit much but can't even fathom a 9spd box.
How far can they go with this before we get road ranger gear boxes in our cars and start splitting gears so we end up with 18spd's in our cars I'm all for fuel economy and technological advancements but how far will this go do you reckon?

[Franco Cozzo]

Probably means they can run a really short diff ratio that they have a massive amount of gears to swap between.

I guess people were probably saying the same thing about going from 5sp to 6sp manuals back in the day? TWO overdrives?!

[Cashie]

Some of the high end makers have said that 8 or 9 speed is probably the limit. I think Mercedes recently stated 8 was the sweet spot in a media review.

[Franco Cozzo]

Surely the case of the thing would be limited in size to fit in a trans tunnel, so wouldn't all the components have to be smaller/thinner? Might not be able to hold up against as much torque as your usual 6sp would?

[bbbero]

I think Ford and GM are working on ajoint project for a 10spd Auto!

[Nova 8]

As mankind continues to develop stronger and lighter component materials coupled with seamless gear changes from auto boxes I see no reason to limit the amount of gears in a car just because people feel uncomfortable with change. I would rather a15 speed auto which changed quickly and smoothly then an older clunky 4 speed auto that takes an age to gear down.

I remember the first 6spd manual I drove years back, I thought it was too many gears and felt like I was constantly changing up and down, now it is the opposite, 5 just isn't enough.

[XR Martin]

Originally Posted by Cashie

Some of the high end makers have said that 8 or 9 speed is probably the limit. I think Mercedes recently stated 8 was the sweet spot in a media review.

Porsche said years ago that 17" wheels was the sweet spot for ride and handling...

[jimmyxr6t04]

The Jeep actually has an 8sp auto. Not sure why the adverts are saying 9? I noticed it say 9 speed too, and then i thought i was hearing things... Glad someone else heard 9 speed!

[mik]

I have driven plenty of 18 speed autos in trucks, and while a a bit less smooth than car autos for obvious reasons, they do the job very well, and with the close ratios engine braking is very nice, even though technically they where really auto shifted manual gearboxes and still had a clutch pedal for starting off , I cpuld see 8 or 9 speed autos in cars being ok, the trade off will probably be weight and more moving parts, how many gears do you really need to move 1 or 2 tons of car or suv?

[wranger]

Grand Cherokee has an 8spd, Cherokee has a 9spd.

[CyberWasp]

Isn't the 8 Speed the same gear box that they had the option of putting in the FH Falcon but aren't going to do?

[Cashie]

Originally Posted by XR6 Martin

Porsche said years ago that 17" wheels was the sweet spot for ride and handling...

And in most applications they probably still are.

But I do get your point though.

[Bent8]

I think 8/9-speeds would work well with less powerful cars (under 300hp) to help keep the revs high for better acceleration and improved economy when cruising.

On the other hand, a 7-speed box in a 500+ hp car is all you really need eg. Aventador - 370kph / Veyron - 430kph.

[Bossxr8]

Ford and GM are doing a joint venture 10 speed that will be in Mustang within a couple of years.

These multi speed autos can skip gears up and down so they are not continually shifting through every gear on the way up/down, so they don't necessarily shift more often than say a 6 speed would.

[GASWAGON]

I still think its overkill these new 8-10 speed boxes.....Whats wrong with the ZF 6 Speeder?

[DFB FGXR6]

Reviews of the 9 Speed auto in the new Cherokee complain that it tends to 'hunt' for the right gear, especially with the base 2.4lt engine.

[Crazy Dazz]

Trucks have always used massive gearboxes because traditionally you're trying to move a massively under-powered load, so you'd have a diesel biased to low-end torque and just keep changing gears to stay in the sweet spot.

The only gripe I have about my current 5spd manuals, is that top gear isn't tall enough for super economical cruising at freeway+ speeds. I otherwise like them, so I think both could benefit from a 6th gear, but also just spreading the ratios would probably work.

[danzvtil]

This is ONLY driven by reducing fuel consumption, not for fun. Global consumption standards continue to tighten.

[chopstar87]

My 300c is fitted with an 8speed auto.... i am a big fan of it.

Very smooth, left in auto, you cant even feel gear changes, is very smooth and is never going hunting for gears, just picks the right one and then goes, has no problem going from 8th straight to 2nd or 3rd when passing someone on the highway. holds gears itself when going up hills without been prompted, so it wont be sluggish at all or jumping up and down gears..

very good for highway Economy, my V6 (210kw - 3.6 V6), sits on 1350rpms at 105kms on the highway, maybe 1400rpm at 110kms. (plus my car will drops to a 3cyclinders as well when cruising) - or if cruising at 60, it will be about 1100rpms in 6th, or if you make it go to 7th, it will sit on 900rpm (but doesn't like that RPM, as its makes the engine lug about at a bit and will shift up pretty quickly to 6th)

When doing spirited driving, and you going in to manual mode via Paddle shifters on the steering wheel, its ratios are similar to a 6 speed, the 7th & 8th only come in to play when cruising on the highway.

[SensationFG8]

Did you do an aftermarket gearbox swap or is that an option to get the 8spd? I thought the 300C's had a 5 speed box!

[Ben73]

I drove an 8sp Grand Cherokee early in the year. It was only a 20 minute drive, but I didn't notice the gear changes in a negative way.
The 3L Turbo diesel was surprisingly powerful, I was more focused on that.

[chopstar87]

My 300c is a V6 petrol, which comes with the 8speed as standard, only the SRT and Diesel models have the 5speed. but i am sure with the update in the states later in the year, the 5 speed will be killed off, as its the last models with in the group (dodge, jeep etc) that has the 5speed.

the 300 and 300c V6 (petrol) have an 8speed, but only have Drive (auto) and Low

My Luxury and now the 300s, have drive plus a sports mode to choose from, plus the paddle shifters, where you can control the gears in either drive or sports modes

[cheap]

There is some parallels to bicycles

Remember the 3 speed hub
Then 10 speed (2 x 5)
Then 12 speed (2 x 6)
Then 16 speed (2 x 8)
Then 20 speed (2 x 10)
Now it is at least 22 speed (2 x 11)

Remember the 2 speed Fordomatic
Then 3 speed
Then 4 speed
Then 5 speed
Then 6 speed
Now 7 speed and 8 speed and more

Each to their own, but sometimes too many gears is just too many gears

But don't despair, in the not too distant future there will be CVT (Constant Velocity Transmission) which will render all the geared transmissions obsolete, it is happening in bicycles

[XR Martin]

CVTs have been around for years yet no one has managed to build them to handle more than 350nm.

[Franco Cozzo]

Originally Posted by XR6 Martin

CVTs have been around for years yet no one has managed to build them to handle more than 350nm.

Crappy box, worst out of the lot and thats saying something.

Even Honda stopped using them and their engines have so little torque they'd struggle to pull the panties off your drunk sister.

[chopstar87]

At the moment, not a fan of CVTs, i drove a new pulsar back from the airport for a work trip. 130kms, highway and city and i wasn't a fan personally.

But i am sure they will improve over time, just like Autos.

Manuals use to faster and more efficient then Autos, now Autos smash manuals for Speed and efficiency, so CVTs will probably develop the same way.

[XR Martin]

Ill admit, CVT in the current Corolla isnt bad and most people couldnt tell the difference.

[Wretched]

Originally Posted by EF_6

I still think its overkill these new 8-10 speed boxes.....Whats wrong with the ZF 6 Speeder?

What was wrong with the BTR 4 speed?
What was wrong with a crank handle?
Wood spoked wheels? hell even the horse and cart?

It's called advancement, I think the advantages have been clearly outlined in this thread.

[madmelon]

Having recently worked in automotive transmission industry...

More gears has a few of advantages:
- Larger spread of ratios, which is particularly important for engines with a low rev limit like diesels
- Smaller steps between gears, making imperceptible shifts easier to achieve
- Larger number of choices to maximise performance whilst minimising fuel economy

ZF, Ford, GM, VW, Mercedes (and probably others) all have 9 or 10 speeds either in the works or in production. From my reading (which is not hugely extensive), the perceived 'ideal' is 9 or 10 speed, according to these manufacturers. Above this, the return on investment is very poor because the economy gains quickly diminishing now.

There are two reasons the gains are diminishing:
1. Engine speed ranges are the limiting factor for NVH in top gear. Basically, there's only so low you can rev an engine with acceptable performance and NVH. The fewer number of cylinders, the higher the minimum rpm- so in fact, the push towards fewer cylinders actually hurts in some ways.

2. A planetary auto generally needs more clutches for more gears. Some of these clutches have to be open to achieve certain gears and every open wet clutch causes a drag. More open clutches = more drag = poorer economy. Add to that the increased friction of more and more stacked gearsets and potentially more bearing and system windage

[simon varley]

it's all about fuel economy, and ensuring that you can get the optimum engine speed under any driving condition. However - I'm really not sure that that last 0.1l/100 is really worth adding $1000 to the car.

A lot is driven by CAFE figures in the states - building low FE cars means they can offset the big F-trucks to still get a good average. Personally I think that's the driver rather than customer wants