6th gear argument rehashed

I just read the link to a thread titled "ZHP & SMG" from a while back. There was an argument that the 6th gear does save gas while others believed it was useless and had no power.

When I was crusing between 65 and 70 miles per house in 6th gear, there was a noticeable "weakness" when accelerating to maintain the speed. I agree that it has enough to slowly push me forward, but it wasn't a lot. I feel much more comfortable at 5th since it has more grunt to plow ahead if I need to.

Now, that brings me to the controversy over whether it saves gas or not. I FIGURE that it probably would save gas assuming it was CRUISING; however, there's a chance it will waste more than it can save. I think it's best to compare it to a multi speed bicycle. When you start off on a low gear you get plenty of power like the low gears on a car. If you were crusing at a fast speed and you were utilizing a higher gear you would notice that it takes considerably more energy to add speed to the bike. Whereas, a lower speed would push you faster with less expenditure of my precious human power.

As always, I'm probably wrong hahaha.. that piece was my best attempt at trying to add tot he overdrive gear argument.

The 6th is an overdrive, and it will save you fuel. With that in mind, 5th will have more power as the engine is spinning faster. Better yet, try 4th - you'll fly!

the conclusion of these arguments was that the gear was strictly for high speed cruising. The gear is mainly used above 70-75. By no means was it to drive uphill or accelerate, but more so to conserve gas on long straight flat highway roads... that and going waaaaaay over the speed limit

Originally Posted by Emission

The 6th is an overdrive, and it will save you fuel. With that in mind, 5th will have more power as the engine is spinning faster. Better yet, try 4th - you'll fly!

Well, yes.. That's obvious enough.
I don't think my statements were clear enough. I think speeding up in 6th gear will waste more fuel than it can conserve. Does that seem valid to you with my bike analogy?

Originally Posted by allaboutme

Well, yes.. That's obvious enough.
I don't think my statements were clear enough. I think speeding up in 6th gear will waste more fuel than it can conserve. Does that seem valid to you with my bike analogy?

Yes. In my limited unscientifically controlled experiments, it seems my car does just as well, if not better, on gas mileage when I shift at high rpms vs. low rpms.

As I said in the previous thread you mentioned, it most definitely is for cruising, not passing, no doubt about that. But if I am on the freeway I use it if there isn't a lot of traffic. It makes for a quieter drive and I have not ever had to shift down due to going up a hill. This includes a 6 mile 7% grade; one of those kind of hills that has a bunch of warning signs on the downhill side and run-away truck ramps filled with gravel. 75 mph all the way up, 6th gear, in cruise control, no problem. And yes, it gets better gas mileage. Probably not a huge diff; like 1 or 2 mpg but that's not the real reason I use it. Just seems more relaxed.

Originally Posted by MysticBlue

As I said in the previous thread you mentioned, it most definitely is for cruising, not passing, no doubt about that. But if I am on the freeway I use it if there isn't a lot of traffic. It makes for a quieter drive and I have not ever had to shift down due to going up a hill. This includes a 6 mile 7% grade; one of those kind of hills that has a bunch of warning signs on the downhill side and run-away truck ramps filled with gravel. 75 mph all the way up, 6th gear, in cruise control, no problem. And yes, it gets better gas mileage. Probably not a huge diff; like 1 or 2 mpg but that's not the real reason I use it. Just seems more relaxed.

Exactly.

I use 6th gear in my car pretty much anytime I'm on the highway at speeds of 60 or better. If I need quick acceleration for some reason, I shift down to 5th or 4th as needed. I commute over 50 miles daily and am able to cruise around 70 to 75 for most of that. My car averages around 23-24 mpg overall. On extended trips, where I have been able to reset the trip computer after a gas stop, the car will get as much as 28 mpg cruising at 75-80 in 6th gear. I have no doubt that it saves gas, is quieter, and saves wear and tear on things. That said, there's a reason for the car having 6 gears, all of them have their need and place in the grand scheme of things.

Over here, in the land of rational speed limits (130kph or higher), 6th gear is great. On the 120 kph stretches, I leave it 5th, as 6th seems to have no positive mpg effect.

In the states, shifting into 6th would seem, uh, well, I guess it's something else to do once you get to 70 mph to occupy your time.

If I bring this car back to the states I may have to swap in a 3.46 or better rear diff to just keep 6th relevant.

Originally Posted by mtbscott

That said, there's a reason for the car having 6 gears, all of them have their need and place in the grand scheme of things.

Yes, particularly for that occasional jaunt to Germany.

Originally Posted by allaboutme

Well, yes.. That's obvious enough.
I don't think my statements were clear enough. I think speeding up in 6th gear will waste more fuel than it can conserve. Does that seem valid to you with my bike analogy?

Are you thinking full throttle of 6th gear is going to use more gas than partial throttle at 5th gear (assuming you are doing 60 and want to get to 80)?

Even though there is more fuel going into each injector at full throttle in 6th, I think that is outweighed by the fact the engine is turning a few hundred times less every minute compared to 5th. I'd imagine those few hundred extra injections of fuel (for the higher RPM) use more gas.

I can see where having a 6th gear on the autobahn would be beneficial, but living in a large metropolitan area it's a complete waste. I'm lucky to see 5th gear in Chicago. Even a trip to the suburbs I wouldn't use it. For people that travel cross country maybe. I really think it's pure marketing.

Guess how many RPM is there between 5th and 6th at 75mph? 180. A measly 180 revolutions a minute.

It's all a marketing ploy. The drivetrain loss from a direct 1:1 gear and an overdrive gear is larger than whatever fuel you're going to save from turning the engine 180 times less a minute. 6th gear is worthless.

Originally Posted by The HACK

Guess how many RPM is there between 5th and 6th at 75mph? 180. A measly 180 revolutions a minute.

180 or 1800?

180 seems WAY TOO low.

The way E46s are laid out, I think it's a really fine line, and depends quite a bit on the car's final ratio. It seems pretty pointless on a 2.93 in a normal 330, but it would really be useful in my car with a 3.46. Naturally, for ///marketing purposes, BMW is going to have to include it in every model, but it would make even more sense if it was properly matched to the proper overall ratio.

At constant speed of 70 mph, on level grade, in 5th gear I am running about 3000-3100 rpm. In 6th a the same speed the engine is running at 2500-2600 rpm. I can usually gain 2-5 more mpg than in 5th.

[QUOTE=The HACK]Guess how many RPM is there between 5th and 6th at 75mph? 180. A measly 180 revolutions a minute. QUOTE]

Hack,

Either your clutch or your calculator is slipping. WIth 25.2" tires, a 3.07 rear screw, and 3000 rpm, in a direct drive 5th gear, your speed is 71.17 mph. When you snick the shifter into 6th, a .85 overdrive, your RPM will drop to 2550 at 71.17 mph. 3000 rpm * .85 = 2550.

Edit: these calculations are for the MY04 330i with ZHP.

Originally Posted by allaboutme

I think it's best to compare it to a multi speed bicycle. When you start off on a low gear you get plenty of power like the low gears on a car. If you were crusing at a fast speed and you were utilizing a higher gear you would notice that it takes considerably more energy to add speed to the bike. Whereas, a lower speed would push you faster with less expenditure of my precious human power.

.

I don't think the analogy works completely. The reason the big gears are tougher on a bike is because they're, well, bigger. So you need to exert more energy for one turn. But you also get more for that one turn in terms of drive.

Here's where the issue is: at what turning rate are you most efficiently exerting force? Depending on your strength, it's a certain number of pedal cranks per minute. If you're in too low a gear, then you have to spin the pedals faster than you're capable. Sure, they're easy to turn, but you burn out your lungs. If you're in too big a gear, you have to use too much muscle, while your lungs are okay--it's like lifting too heavy a weight. Your muscles get burned, while your lungs aren't fully exerted. You want a happy medium.

Same thing with an engine: you want to be at the most efficient running point in terms of power/fuel consumption. Obviously, you don't drive in 6th speed around town, because the engine isn't powerful enough at 20mph to turn the wheels. At highway speeds, the engine goes too fast and blows out.

So, to answer the question, you have to figure out a) what's the most efficient point for the engine to be operating, which is generally the highest gear in which it's not lugging at the speed you're going. IF that's 6th, use 6th. If not, use a lower gear. If you have to go up hills regularly, and the engine lugs, well, you need to shift down. BUt you're not going to waste gas by shifting down, because you're using a more efficient gear.

Originally Posted by Emission

The 6th is an overdrive, and it will save you fuel.

How are you so sure? This is an awfully general statement. Despite seeming intuitive, the statement is not guaranteed tob e true. Would a 7th, 8th, and 9th save gas? How can you be certain that 5th gear isn't the sweet spot for certain cruising speeds in the E46?

I don't use 6th unless I'm using the cruise control and driving over 75mph (I have the 2.93 diff).

Originally Posted by Tanning machine

So, to answer the question, you have to figure out a) what's the most efficient point for the engine to be operating,

Agreed.

which is generally the highest gear in which it's not lugging at the speed you're going.

Hmmm. You sure? Is this based on intuition, or data? I can imagine it's possible for there to be some gap between "ideal efficiency" and "lugging".

Originally Posted by allaboutme

Now, that brings me to the controversy over whether it saves gas or not.

When cruising to Florida last month, our first stretch of the trip we received 33 MPG using 6th gear. And that was with the perf. pkg.'s shorter rear end gearing. Averaged over 30 MPG for the entire trip. Average speed was about 77 MPH.

But at lower speeds, and more typical in-town driving, I doubt that 6th will do anything but make your mileage worse. Too tall a gear for frequently changing speeds.

In an ideal world, that rpm at which the engine produces exactly the horsepower required, after drivetrain and aerodynamic losses, to maintain a given velocity is the optimum rpm for economy, as the engine is using precisely the minimum amount of burned fuel required to produce that horsepower with no excess fuel or HP created.

But, the real world has variables in driving, requiring acceleration. An engine accelerates most effeciently (fuel required to achieve desired HP) at the peak of it torque band--that point at which the engine most effeciently produces power. The fat part of the torque band is rarely down at that minimum rpm needed for steady state driving.

So, driving through Florida, very flat, near sea level with lots of air density, and few variations, you'll get higher mileage. So ff can pop 33mpg. But, if he goes to Northern Alabama, the constant acceleration required to go up hills and avoid pick-up trucks loaded with hunting gear (no flames--I used to own one!) means his mpg will drop since periodic acceleration is required.

Not to change the subject...well it's sort of the subject....but anyway I have a 2004 330i on order with the 6speed. Based on what I've read the first 5 gears are the same as any other E46 up to 2003 right? So in another words, my driving experience with the 6speed is going to be exactly the same as anyother E46 with the 5speed except that I have one more overdrive gear right? My last car was an 04 STi and that had a 6speed. It was my first 6speed as all my other cars had 5speeds. With the STi there were plenty of times when by force of habit I wanted to go to 2nd, but as I got used to the 6speed I was using 3rd instead. So in this case the 6speed was a completely different experience from the 5speeds I had been used to, but with my 04 330i the first 5 gears will be the same as the other E46 5speeds, but I will simply have an extra overdrive gear?

Originally Posted by Moderato

I have a 2004 330i on order with the 6speed. Based on what I've read the first 5 gears are the same as any other E46 up to 2003 right? So in another words, my driving experience with the 6speed is going to be exactly the same as anyother E46 with the 5speed except that I have one more overdrive gear right?

Correct, unless you got the Performance Package, which includes a slightly shorter final drive.

Oh come on guys. Don't you think that if the 6 speed got better mileage that BMW would say so to up their overall mileage rating with the US Govt? The five speed 330s and six speed 330s are still both rated at 30 highway and 24 city. My guess is that there is no difference. I just drove from Seattle to LA, with an average of 73 MPH at 29.5 MPG. Not bad for a five speed. I truly doubt that the six speed is anything but a marketing ploy.