Why isn't 6th gear super tall?
 

Just got a 03 Audi 6 speed v6 A4. mpg is 27 going about 80 mph all day.
RPMs are 3000 going 80 when V6 horsepower can easily move the car in any gear at 2000 RPM. Why don't car makers make a super efficient 6th gear to drop the RPMs so it get super highway MPG?

They build it to get good number on the EPA test cycle and the EPA test cycle doesn't go that fast. They want the sweet spot to be at the test speed. There is probably also a point where the gears would be too much of a drop in RPM or just too much strain on the parts themselves. There is also a limit in the size of a transmission between the input and output shafts that the difference in what the lowest gear to the highest gear can be. To make that separation bigger they would have to increase the separation of the shafts. So it's probably a combination of all 3. I bet bottom line, if they could make the EPA number better they would do it even if they had to re-design everything else to work with it.

^^ there's probably truth in that. And I'd also add that customers might complain that the car feels a little "doggy" with taller gearing, which would be a marketing problem for them.

Gearboxes in general are classified as close-ratio and wide ratio. Close-ratio is for sportscars, wide-ratio is for trucks. If sixth is raised at the very least fifth would have to move as well.

Audi might want to sell to people who ski, with lots of friends.

I had a auto two gear ford falcon, a 3 gear mustang, multiple 4 gear trucks and cars . Many 5 speeds. Now I got this 240 hp 6 speed . If I'm just coasting around, I skip gears due to getting bored with all the gears. I say " I want 5 gears for driving, and if there is a a 6th. It better be frickin tall so I save gas on the freeway. gosh darn it!
Yes, I do rev it up and enjoy the heck out of it, but I can't act like a 17 year old all the time anymore.

Permalink, if I drive 40 mph in 6th, I get 40 plus mpg on display, tach shows about 1700 rpm. Engine takes it fine, no knock or lug. I see your point. EPA tests and all. Avg fleet mpg. Still a taller 6th would seem to help make the results better. It would also increase top speed I reckon.

This is among my favorite gripe topics. Your gearing is way better than my Acura. My 6th gear has me doing about 65 MPH at 3000 RPM.

The thing is, 6th is completely worthless as a racing gear. It would take several miles of a straight racetrack for me to top 5th gear out. A jumbo jet runway isn't long enough for me to reach 6th in a drag race. But, it's so short that it isn't any use cruising on the highway at 60 MPH either.

It sucks at everything!

If Acura had programmed the VTEC to kick in at somewhere less than 6,000 RPM (yes, that is when it begins to work), then the gears wouldn't have to be so closely spaced.

I've thought about putting an RSX final into the TSX, but it would only marginally help tame the RPMs.

Other than that, and the car having the turning radius of a train, it's a perfect car.

I put a five-speed in my (normally four-speed) VW Type III notchback. I shifted up into fifth at 85mph.

The advantage came in having one more choice for gearing driving around town.

The new Civic Si has an amazing 6-speed. 1-3 is as short as the old NA Miata's (VERY short). Then 4-5 is fairly tall, and 6th is really tall. I believe 6th at 80mph is 3000rpm. I know 6th at 70 is 2700, which is about what the honda insight is in 5th. Guess that's why it's rated for 41mpg highway.

Most of the times a 6th gear is worthless at all, and sometimes a 5-speed transmission may actually lead to a better mileage compared to a 6-speed. But anyway, instead of a taller 6th, if I had the choice I'd get a wide-ratio transmission with a higher gear spread and match it to a higher differential.

My 2.0 petrol auto is geared to 28mph per 1000 rpm in top. It is a four speed. Ratios must be quite wide apart. Getting between 37 and 40 imperial mpg. Which is what manufacturer says is maximum mpg under ideal conditions. I drive far from ideal conditions. Hills strong winds and sub zero temps for 3 months of year.

Yea I'm doing the opposite in the Miata. I'm doing a really short geared 6-speed swap (gears 1-6 are actually shorter than the 5 speed 1-5), but I'm pairing it with the tallest rear end available for the NA Miata (3.63 instead of 4.1) So my 1-5 is the same ratio as the 5-speed with 4.3 rear end, but 6th gear is a true overdrive and makes driving the car a dream. My RPM will drop about 500 over the 5-speed with 4.1 (from 3636 at 75 to 3150(ish), and 750rpm over the 5-speed with 4.3.

I used to skip shift my 6 speed and start in 2nd until I was told that was bad overall for mileage and wear and tear. This is on a Cummins diesel with 600 ft-lbs of torque on tap. If anything would work well with a 2 speed powerglide this would. I went with a tad taller tire 33" vs 31.5" stock) to drop freeway rpm. Now I run about 2000 rpm at 70mph and that seems to keep exhaust temps pretty low. It does get better mpg at 60 but the EGTs go through the roof towing with any throttle under 2000 rpm. So any acceleration or hill I always downshift and just use 6th for steady crusing. The NV5600 starts with a 5.63 in first and ends at 0.73 in 6th but it is a beast. Probably heavier than most 4 cylinder engines at 360 pounds.

Manufacturers don't put in tall top gears because they are concerned people will think the car is slow when they floor it in top gear and don't bother shifting down. "Gotta have good top gear roll-on performance, guys, nothing else matters. Its not like there are 5 other gears to choose from."

1st gen insight is at 2392 RPM at 70. New civic Si is at 2626 RPM at 70. Almost spot on Balto, 80 mph is 3001 RPM! :p

My accord V6-6mt does 2312 RPM at 70 with my 25.7" tires instead of 25.5" stock which does 2330 RPM.

A 2017 Base model Vette 7 SPEED MANUAL does 1256 RPM at 70. WANT.

Meanwhile my CBR 250R did 9289 RPM :eek: at 70 stock, now at 8773 with 3 teeth down on the rear sprocket.

Q: Why?

A: Look up the definition of "lugging" as applied to the Internal Combustion Engine.

Lugging>>sweet spot>>valve float.

Yea but no car is going to lug at 2500-2750rpm. Even going up a 10% grade in top gear at WOT. Even the insight won't.

I don't know the specific case of your truck, but anyway, skip-shifting is not so bad depending on traffic and terrain conditions.

Great stuff! If I'm going down hill or on level road I often skip shift. 1st 2nd 4th 6th. If the car is rolling at 2 mph, I will stick it in 2nd and gently accelerate up to speed.i don't think starting from a stop in 2nd is a great idea, 2nd gear seems like the most abused and worn out gear in my older cars. And clutch wear will be heavier starting in 2nd.

I like the idea of trying taller narrower tires to lower the rpm.

Here is a,link about Lug and Coast
https://www.caranddriver.com/columns...-lug-and-coast

My Insight seems very happy at 1200rpm. It's only when it dips down to 1000 or below that it starts to sound/feel rough.

That said, a taller 5th wouldn't be of much use in this car on level ground, much less hills. I feel like Honda nailed the top ratio. I wouldn't mind closer spacing and an extra gear where the current 1-2-3 are though; RPM nearly halves with each shift.

I've never had much luck with the skip shift, maybe because my Civic has as much torque as an electric toothbrush. But lugging is rare, and despite the engine's smooth yearning for high RPM, it's fine from about 1200 or so RPM, provided you aren't being super aggressive. Pulse and glide feels like it needs 1300rpm to keep from being too weirded out by heavy throttle inputs.

In high school and college I drove International box vans ('54 to COE) that had a five-speed box and two-speed rear axle with an electric mushroom switch strapped to the gearshift lever.

Split shifting up and down. ...or not.

When PSA (Peugeot/Citroen) moved from 5- to 6-speed trans with the 1.6HDi engine, the new 6th gear was only like 2% taller than the old 5th, but you had more intermediate choices, making it easier find the right gear for the speed and load.

VW Beetles have a high fourth anyway, the conversion used a 'low-fourth' with a 'high-fourth' kludged on. I have the build sheet around somewhere, I don't recall if third was moved.