Why don't more cars come with 6 gears as standard?

mick.fr

Run_to_da_hills wrote: »

Anything over 3 or 4 gears is bunk, older engines had great torque and had real power. With these modern high revving engines you spend all day flipping up and down gears, realistically these motors couldn't burst their way out of a wet paper bag!:D .

Mustang GT had a average HP of 250.
A 4 gear alright, but still average power nowadays.
A 6/7 gear is really about the maneuverability of your car at low speed I believe, correct me if I am wrong.
It is pretty easy to hit a mall's wall with a Mustang GT if you are not used to the gearbox.

Run_to_da_hills

mick.fr wrote: »

Mustang GT had a average HP of 250.
A 4 gear alright, but still average power nowadays.
A 6/7 gear is really about the maneuverability of your car at low speed I believe, correct me if I am wrong.
It is pretty easy to hit a mall's wall with a Mustang GT if you are not used to the gearbox.

The Mk 1 Camero was the same, (3 Speed) driving these cars involved more skill, they never made it over here, I suppose the equivilant car would have been the Ford Capri which also origionally came with just a 4 speed box,

-Chris-

As previously said, cogs are added in the middle, rather than at the top - i.e. 5th gear in your 5-speed car is pretty much the same as 6th in someone else's 6-speed car.

Putting more cogs in the middle makes it easier to keep your car within the very narrow powerband that modern cars are now operating with. As rightly pointed out, large capacity engines (like a big old V6 or V8) will have buckets of torque and therefore not need many gears.
The trend for medium and small cars is for the engines to get smaller and more efficient, but the trade off for this is for the powerband to narrow and 6-speeds to be necessary.

Biro

The VW TDi 6-speed means that it's around 400 rpm lower at 100km/h than the 5 speed. (This is the case in the Passat anyway, maybe the Golf etc 6-speeds are different ratios).
I find it only for economy in a turbo diesel, as the engine has more than enough torque not to need the extra cogs in the mid range.
The gen 7 celica would happily sit in 6th from 40mph, not even hinting at labouring.

colm_mcm

mick.fr wrote: »

the M6 has 7 gears if I am not mistaken, looks like we are gonna hit 8 gears in a couple of years lol

The Lexus LS460 has a sequential shift 8 speed auto

AudiChris

AudiChris wrote: »

As previously said, cogs are added in the middle, rather than at the top - i.e. 5th gear in your 5-speed car is pretty much the same as 6th in someone else's 6-speed car.

Putting more cogs in the middle makes it easier to keep your car within the very narrow powerband that modern cars are now operating with. As rightly pointed out, large capacity engines (like a big old V6 or V8) will have buckets of torque and therefore not need many gears.
The trend for medium and small cars is for the engines to get smaller and more efficient, but the trade off for this is for the powerband to narrow and 6-speeds to be necessary.

More cogs... More like cogs with different ratios. Where they are added is a bit of a red herring. The ratios would generally be different on all the cogs in a 5 speed and 6 speed.

colm_mcm

top gear in a 6 speed generally makes the engine rev lower than on a 5 speed. On a very high performance or luxury car, the very top gear would be useful for very high speed cruising, as in the LS.

-Chris-

ronoc wrote: »

More cogs... More like cogs with different ratios. Where they are added is a bit of a red herring. The ratios would generally be different on all the cogs in a 5 speed and 6 speed.

Sorry, that's what I mean. You keep the top ratio the same, but the number of middle ratios increase and the ratios are changed.

There's actually a formula for calculating gear ratios for an engine, using the rpm of max torque and rpm of max power. I can't remember it though, I'm a bit rusty on the aul vehicle engineering.
You then need to take into account the final drive ratio in the differential and the rolling circumference of the wheels to calculate the speed of the car in a given gear at a given rpm.
The principle holds though, that you match the gears to the power and torque characteristics of the engine. It's not as simple as adding an additional 6th gear to an existing 5 speed gearbox to give you a lower rpm at cruising speed.

Onikage

Spot the difference:

Timmaay

I've heard of a good few people with 1.9tdi engines changing the 5th gear ratio (ie, swapping 2 of the cogs in the gearbox), so as the car will rev lower on motorways and save fuel. It's a bit extreme I'll admit, just to get a small mpg improvment, while basically making 5th gear useless for overtaking/accelerating.

colm_mcm

guys, 6 speed gearboxes are useful, e.g I'm driving an Avensis D-4D 6 speed, and the 6th gear is noticibly longer than on the 5 speed model. If the current 6th gear ratio had been used on the 5 speed box, the gears would have to be farther apart, and it'd be hard to keep the engine in its power band. 1st gear is also shorter than on the old Avensis, so taking off from a standstill is quicker and easier.

-Chris-

Onikage wrote: »

Spot the difference:

Best answer yet!