What's your worst fuel economy on a single tank?

[BrokenVert]

None of this answers my question. At what RPM does the engine in the 1M turn at 60...you know the important metric for comparing fuel efficiency...

Originally Posted by Simsims

don't know - car is parked for winter

But do realize the first thing i noticed in the 1M was the gearing.
In "normal" city driving I tend to cruise around in 4th gear (60km/h)
With 1M I'd be in 3rd gear instead, if the RPMs are to be within the same range.

http://www.bokchoys.com/differential/GearRatios.htm

1M uses M3 final diff of 3.85
and 135's ratio is 3.46

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Edit - that's kind of weird. Shouldn't a bigger final gear ratio make your other gears "slower"? What I experienced was the reverse.

That's weird

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Edit again: Each turn of 1M wheel is 6.27% more distance than 135 (bigger rim/tire). That'll offset some of that gear...

[tkbr0wn]

Originally Posted by BrokenVert

yeah I have a vert. But its the same engine and gearing

You're original statement was false. He said it was different then you questioned him.

Originally Posted by BrokenVert

what does your engine turn at 60? Also my car doesnt have "air curtain technology" so it balances out :P

The answer to your question would be that they turn different RPM's at 60mph. You can do the math with the final drive ratios.

[BrokenVert]

Originally Posted by tkbr0wn

You're original statement was false. He said it was different then you questioned him.

The answer to your question would be that they turn different RPM's at 60mph. You can do the math with the final drive ratios.

Why is this such a difficult question to just answer?

I didnt feel like doing the math, and since we have a whole forum of 1M owners I simply decided to ask at what speed their engines turn at 60. For just cruising transmission gearing makes no difference if the engines turn the same speed in 6th. Knowing that number makes gearing irrelevant to the equation.

As there are 4 main factors that determine highway efficiency at a given speed.

1) engine speed (what im trying to find out)

2) engine displacement (its the same engine, dont give me the blah blah blah different programming, off boost its the same damned engine)

3) Tire rolling resistance (higher for the 1M)

4) aerodynamic drag (we have these numbers as well. Its .37 published for both my vert and a 1M coupe)

[Dan Parker]

No one answer that question.

[BrokenVert]

Originally Posted by Dan Parker

No one answer that question.

you guys suck

[tkbr0wn]

Im no engineer, so this is an honest question... Did you just say that if the 6th gear ratios are different that the engine speed could be the same at 60mph? (Lets take tire sizes out of the equation for now).

Do you have an auto or a manual?

[BrokenVert]

Originally Posted by tkbr0wn

Im no engineer, so this is an honest question... Did you just say that if the 6th gear ratios are different that the engine speed could be the same at 60mph? (Lets take tire sizes out of the equation for now).

Do you have an auto or a manual?

Yeah, even if none of the number match, the 6th gear ratio, final drive ratio, and tire sizes can all conspire to make two seemingly different cars turn the same speed at 60.

Its not that uncommon actually, youll find that most cars run at between 1800 and 2200 at 60 despite the wide range of makes, models, car size, etc represented. Its done that way on purpose.

[tkbr0wn]

I specifically stated to take tire sizes out of the equation. So two different cars with identical tires are traveling at 60mph in 6th gear. Each car has a different 6th gear ratio. Are you saying that the engine speeds could be the same?

I'm just confused as your first post used gearing in the argument, and now gearing doesn't matter. Trying to put it all together in my head.

[BrokenVert]

Originally Posted by tkbr0wn

I specifically stated to take tire sizes out of the equation. So two different cars with identical tires are traveling at 60mph in 6th gear. Each car has a different 6th gear ratio. Are you saying that the engine speeds could be the same?

I'm just confused as your first post used gearing in the argument, and now gearing doesn't matter. Trying to put it all together in my head.

Yes, the 6th gear ratios can be different and the engines turn at the same rpm at a given speed. The final drive can alter it enough as you havent defined it to a number.

Gears are wonderful things, you can do basically anything you want with them.

I included tires as part of the gearing, because technically the wheel size operates effectively as a gear of that size. Different size tires can be equated as two different size gears. And when I used gearing in that context. I used overall gearing, as in the stuff between the engine and the road (tires, final drive, gearbox)

I stated that with fair certainty because like I said, car manufacturers usually shot for the engine to turn at 2K rpm at 60. Its the normally determined speed that is both considered good for fuel economy and for passing power.


This is also why corvettes get such great mileage. They have super torquey engines, so they can be run safely at low RPM, they burble around the highway just above idle basically and manage the same economy numbers as a 1M, despite having an engine thats over 100% larger.



But none of this is the point of the conversation! ha

Super treadjack and im sorry about that

[tkbr0wn]

On the way home now. 1900 RPM @ 60 in 6th.

[BrokenVert]

Originally Posted by tkbr0wn

On the way home now. 1900 RPM @ 60 in 6th.

So with all other factors just about equal. You can deduce that a 1M should be theoretically capable of matching my gas mileage that I posted earlier in the thread.

[Dee Pee]

I got 20.5 on ethanol-free fuel (4 tanks) and 18.5 on Chevron Supreme unleaded that has ethanol (4 tanks).

[Simsims]

Originally Posted by BrokenVert

So with all other factors just about equal. You can deduce that a 1M should be theoretically capable of matching my gas mileage that I posted earlier in the thread.

you forgot to factor in:
- Higher drag coeff for 1M
- Wider tires
- Different tread pattern/friction coeff
- Auto vs Stick.

135 auto and stick have different gearing. You're comparing apples and oranges. All I can say is my 1M cruises at lower RPM than my 135.
Best I got was 9.9L/100km but that's on the autobahn, so I probably drove around 130/140km/h; plus the car isn't fully broken in.
Best I got in my 135 was around 8.xL/100km.

[BrokenVert]

Originally Posted by Simsims

you forgot to factor in:
- Higher drag coeff for 1M
- Wider tires
- Different tread pattern/friction coeff
- Auto vs Stick.

135 auto and stick have different gearing. You're comparing apples and oranges. All I can say is my 1M cruises at lower RPM than my 135.
Best I got was 9.9L/100km but that's on the autobahn, so I probably drove around 130/140km/h; plus the car isn't fully broken in.
Best I got in my 135 was around 8.xL/100km.

I did address them in previous posts

[urban_alchemist]

I'm getting about 210km on 3/4 of a tank. Economy is not the car's strong point (though that might have something to do with how it begs to be driven)!

[hythe]

Computer reckons I'm getting about 12mpg (imperial) on my daily commute.

[HALOTHANE]

19.2 mpg mixed city/highway

9 mpg track day at Homestead

[Pete_vB]

Originally Posted by BrokenVert

I did address them in previous posts

He's absolutely correct- you might have mentioned these issues, but that doesn't mean you addressed them (correctly).

Again. You own a 135i, not a 1M. They are different cars. Your "math" doesn't make them the same.

Some of the bigger errors in assumptions you're making:

Drag is a function of Cd x frontal area. The 1M has significantly larger frontal area (fender flares, more tire width) and hence CdA (total drag).

Rolling resistance- larger rolling diameter for the 1M means lower rolling resistance, however the type of tire will generally dominate.

Gearing- "close" (and it's not that close percentage wise) doesn't cut it.

Engine- tuning makes a difference.

Weight- different, impacts rolling resistance...

I could go on. They are different cars. They don't get the same economy.

[BrokenVert]

Originally Posted by Pete_vB

He's absolutely correct- you might have mentioned these issues, but that doesn't mean you addressed them (correctly).

Again. You own a 135i, not a 1M. They are different cars. Your "math" doesn't make them the same.

Some of the bigger errors in assumptions you're making:

Drag is a function of Cd x frontal area. The 1M has significantly larger frontal area (fender flares, more tire width) and hence CdA (total drag).

Rolling resistance- larger rolling diameter for the 1M means lower rolling resistance, however the type of tire will generally dominate.

Gearing- "close" (and it's not that close percentage wise) doesn't cut it.

Engine- tuning makes a difference.

Weight- different, impacts rolling resistance...

I could go on. They are different cars. They don't get the same economy.

Actually drag is far more complicated than that...but why would I know. Im only an aerodynamicist
The 135 has less frontal area, but I can guarantee that my vert with its top open (as was the case on my trip with published figures) generates more drag than a 1M in any scenario.

Also drag is a function of two different types of drag. Skin friction drag and form drag. The 1M probably produces more friction drag (that "formula" you quoted of Cd X frontal area, which in itself is so massively simplified that it means nothing) but my car produces far more form drag for a myriad of reasons that honestly wont make sense to someone who isnt versed in aerodynamics (not a shot, its just really damned complicated stuff)

Rolling resistance - I generalized that bit and admitted to that. I was on my 245 square setup of star specs...theyre pretty sticky. I think that one is too close to call.

Gearing, I already proved this one. If the engines turn at the same rate at a given speed than the overall gearing is the same. It was posted that a 1M turns 1900rpm at 60 mph. My 135 turns about 1850 at that speed, again so close it doesnt make a difference.

Engine. The tuning differences in the otherwise identical N54s in both of our cars is almost entirely boost adjustments. These make no difference when the car is off boost. Which it is at a slow highway run.

Weight. My car weighs 300 lbs more than a 1M, so by your logic, my heavier car on slightly smaller rubber provduces more parasitic drag than yours does.





I could go on as well, in fact I have. But they are similar enough to have comparable numbers.

Or did you forget that your driving a 1 series with an N54?

[Pete_vB]

Originally Posted by BrokenVert

The 135 has less frontal area, but I can guarantee that my vert with its top open (as was the case on my trip with published figures) generates more drag than a 1M in any scenario.

So more apples to oranges...

Originally Posted by BrokenVert

Gearing, I already proved this one.

Proved? You think so? Man, I'd hate to fly in any plane you designed...

Originally Posted by BrokenVert

Engine. The tuning differences in the otherwise identical N54s in both of our cars is almost entirely boost adjustments. These make no difference when the car is off boost. Which it is at a slow highway run.

And the exhaust drone in the 1M? You don't think exhaust design effects BMEP/ efficiency?

300 lbs difference... more oranges.

So you've "proved" your car gets the same mileage as the 1M. Unfortunately the EPA says otherwise...

[BrokenVert]

Originally Posted by Pete_vB

So you've "proved" your car gets the same mileage as the 1M. Unfortunately the EPA says otherwise...

Thats not what ive proved at all.

I was simply proving that the 1M can match my mileage. Subtle wording, big difference. Maybe you should understand my argument before you try refute it

[chachacha28]

My dash says my average for this tank is 16.1mpg right now. I tend to drive pretty fast though, and i just got my DCI installed, so i get on it even more just to here that glorious noise!