Why don't more cars have taller final gears?

[fuzzybabybunny]

I have a Honda Fit and in 5th gear I'm doing about 3.5K RPM at 70mph. My old Toyota Echo does 3K RPM at 70mph. Assuming that a lower RPM will use less gas, why don't more manufacturers put a six speed gearbox in their econo cars, with the final drive able to do something like 70mph at 2.5K or 2K RPM - intended solely for cruising? Wouldn't that save gas? At that gear ratio with a 120hp motor, the air resistance wouldn't stress the engine too bad (resulting in less economy), would it?

 

[alpineranger]

Hondas traditionally have super short gearing on the manuals. I think it's a combination of several things: 1) sporty feel - better engine response / passing power , 2) their engines may not benefit from it very much, having poor power and high bsfc at low rpms 3) there is little / no benefit on the epa numbers (these are conducted at lower speeds).

 

[alkemyst]

6 speeds are more expensive to manufacture than 5....plus many are re-using common parts in the econo cars.

Gearing is a complex thing. It's a combination of response, economy, top speed, towing, etc.

They try to hit the average buyer's range rather than please specific ones.

 

[StageLeft]

I have wondered the same. It cannot cost THAT much to have a 6th gear in a typical 5 speed that has super tall gearing. My Maxima at highway speeds also needs a good 3k to cruise. It does always have strong response even without a downshift but still I wonder what its mileage could be if it was cruising at 2k...

 

[LTC8K6]

I cruise at a fast idle with the hemi...

 

[Ronstang]

It has to do with the amount of power to keep a car moving at speed. Little engines make what little torque they do at a higher RPM. If you do not keep the RPMs high enough the engine lugs and becomes less efficient.

Case in point. My 85 GT Mustang had a tall 2.85 rear gear and when in 5th gear (overdrive) the engine would only be doing 1500 RPM at 55 mph (the legal limit back then) and deliver 25 MPG on the highway....simply going 70 MPH and getting the RPM up to 1700 netted 27 MPG. The engine simply was out of it's optimal torque range at 1500 RPM and even the extra load of 15 MPH more had less of a negative impact on mileage than being at a more efficient RPM had a positive effect.

 

[alkemyst]

automakers decide costs based on pennies of production...

 

[PlasmaBomb]

automakers decide costs based on pennies of production...

Beancounters...

 

[ayabe]

Right you could get a much taller 5th or 6th and then you wouldn't be able to use it in the city. It's a pick your poison kind of thing, I'm with you guys but most people do their driving in the city at 45-60mph not cruising on the interstate at 80.

 

[angry hampster]

I have a Honda Fit and in 5th gear I'm doing about 3.5K RPM at 70mph. My old Toyota Echo does 3K RPM at 70mph. Assuming that a lower RPM will use less gas, why don't more manufacturers put a six speed gearbox in their econo cars, with the final drive able to do something like 70mph at 2.5K or 2K RPM - intended solely for cruising? Wouldn't that save gas? At that gear ratio with a 120hp motor, the air resistance wouldn't stress the engine too bad (resulting in less economy), would it?

A Fit wouldn't be able to accelerate at 70mph at 2000RPM.

 

[HarryLui]

A Fit wouldn't be able to accelerate at 70mph at 2000RPM.

Forget accelerate. It will probably have problem maintain that speed.

At WOT probably.

http://www.hondanews.com/categories/872/releases/4703

 

[MJinZ]

I have a Honda Fit and in 5th gear I'm doing about 3.5K RPM at 70mph. My old Toyota Echo does 3K RPM at 70mph. Assuming that a lower RPM will use less gas, why don't more manufacturers put a six speed gearbox in their econo cars, with the final drive able to do something like 70mph at 2.5K or 2K RPM - intended solely for cruising? Wouldn't that save gas? At that gear ratio with a 120hp motor, the air resistance wouldn't stress the engine too bad (resulting in less economy), would it?

They do, you just bought the wrong Econobox.

A Toyota Camry would have 6 gears.
Ford Fusion would have 6 gears.

Etc etc

 

[Demon-Xanth]

Different engines have different sweet spots. In my truck with my engine, it's actually in an odd scenario that I get the same gas mileage at 65 as I do at 80. The sweet spot happens to be about 2500RPM, but my gearing puts it at about 2000 on the freeway. People that have the 3.92 rear end (instead of my 3.55) get the same MPG. When I swapped out my rear tires for ones that had a slightly larger diameter my gas mileage actually went down a half an MPG (yes, I corrected the mileage for the tire size).

Read up on "BSFC" as referenced in alpineranger's post and you'll see why.

 

[MJinZ]

Right you could get a much taller 5th or 6th and then you wouldn't be able to use it in the city. It's a pick your poison kind of thing, I'm with you guys but most people do their driving in the city at 45-60mph not cruising on the interstate at 80.

That's just wrong. 80% of drivings is done on highways over 60mph.

 

[Capt Caveman]

They do, you just bought the wrong Econobox.

A Toyota Camry would have 6 gears.
Ford Fusion would have 6 gears.

Etc etc

Those aren't econoboxes.

 

[ayabe]

That's just wrong. 80% of drivings is done on highways over 60mph.

So most people travel at interstate speeds everyday? Uggh Nope.

 

[WhoBeDaPlaya]

My LS cruises 70mph at 2K rpm. IINM, ZV mentioned the Grand Marquis doing 1750rpm.

 

[MJinZ]

So most people travel at interstate speeds everyday? Uggh Nope.

Yes.

 

[MJinZ]

Those aren't econoboxes.

Sure they are. Get the cheapest one for like $17-18k.

Isn't that how much the OP bought his/her Fit for, like $16.5k?

 

[Kirby]

I wish my car had a sixth gear, I have about a 20 mile commute on the interstate everyday. 3k RPM @ 70 mph, and I usually drive around 78.

 

[overst33r]

My LS cruises 70mph at 2K rpm. IINM, ZV mentioned the Grand Marquis doing 1750rpm.

I think the lowest I've seen at 70mph is the C5 corvette, which is like 1300-1400rpm or something like that.

My car does 3700rpm at 70mph and 4200rpm at 80mph.

Can't wait to get a Z06!

 

[DivideBYZero]

yes.

lol

 

[KIAman]

Not only will the econobox not be able to maintain speed at such tall gears but also any imperfections in the road or the grade would force the gearbox to continually downshift. I am pretty sure the econoboxes are geared with just enough threshold for extra power, economy and speed.

 

[Perknose]

Hondas traditionally have super short gearing on the manuals. I think it's a combination of several things: 1) sporty feel - better engine response / passing power , 2) their engines may not benefit from it very much, having poor power and low bsfc at low rpms 3) there is little / no benefit on the epa numbers (these are conducted at lower speeds).

These (reasons.)

 

[yh125d]

WTB 6th gear in my 06 fusion. 3500RPM at 80 is not fun. Especially considering I know it can easily maintain 80 up steep grades at only 2800 >.>