[natedog7700]

At what speed does the MPG begin to drop on the freeway? I would like to know for 335i's because i have one but if anyone knows for a different model please share!

[hassmaschine]

65 seems to be peak for my 330i - that said,it doesn't really seem to make much difference if I'm going 55 or 80, on long highway runs it still averages about 33mpg.

Since all E9x's are basically 3.0 liters (in the US anyway) and have the same areodynamics, I wouldn't expect it to vary much. The primary difference will be gearing and AT vs MT. The 330i mt for example has relatively long gears compared to other models.

[Captain comic]

What hass said. I just will add that IMHO it's around 50mph. I read an extensive article where they compared different setups, engines, transmissions and surprisingly all of them showed better efficiency at around 50mph. Final gear ratio and aerodynamics matter of course, but for max efficiency slower 50 beats real life 65mph

P.S. That been said - this is purely theoretical question as in real life you won't be able to maintain 50, even in right lane - you'll get honked and screamed by every minute - it's just not worth it lol

[401FlaGATOR]

The slowest you can go in the highest gear is what has been discussed before, the sweet spot is from 40 to 60 for most cars on the road, with trucks being closer to 40 and more aerodynamic cars being closer to 60. Air resistance is the factor, there is an interesting video from Engineering Explained's Jason Fenske that explains it mathematically:

[BSM n54iS]

95

[racermp]

I turn off the car after 120. Seems to work great but then I need to turn it back on when I get down to 60

[robthewrench]

For most vehicles it is usually the slowest speed in the highest gear. For the e90, this would be 50-60 when the auto trans kicks into 6th gear and you cruise along in 6th.

Aerodynamic force is the primary negative force against the car and this force goes increases exponentially with speed. (v^2). So going twice as fast results in way more than twice as much resisting force.

You can really only achieve this ultra efficient mode off the interstates. You'll be an accident risk trying to drive 50-60 on most interstates. But the underlying formula still holds true, slower speeds will yield better fuel economy.

[weehe126]

Well, seeing as I actually have a 335. I notice a massive drop in mpg once I cross 75mph. At 65 mph I get 30mpg, 70mph 28-29mpg, 75mph 23mpg, 80-90mph 20-21 mpg. Now every car will be different as aero will actually play a roll at these speeds.

[Unknown_Car]

On my 335 is about 55mph.

[mweisdorfer]

I have got 30.5 miles per hour with my n54 going mostly 80mph on a hwy trip of 500 miles. maybe 60 of those miles were at 60mph because I was in a 55 zone.

[Eddien123]

I saw a report once where it said at 50 MPH your engine only needs to produce like 7-14 HP to keep you going. But the real answer is it varies for every car. Whatever the speed in which your car shifts into 6th gear is. So if your car shifts into 6th at 46 mph like mine, then somewhere around there is the best. I've seen 36-39 mpg with my car doing 45 mph for 15 miles before. Highway speeds add more drag and require more power.

[floydarogers]

Originally Posted by Eddien123

I saw a report once where it said at 50 MPH your engine only needs to produce like 7-14 HP to keep you going. But the real answer is it varies for every car. Whatever the speed in which your car shifts into 6th gear is. So if your car shifts into 6th at 46 mph like mine, then somewhere around there is the best. I've seen 36-39 mpg with my car doing 45 mph for 15 miles before. Highway speeds add more drag and require more power.

Lots of good answers in this thread; I like this summary.

My 335d doesn't get into 6th until 48mph; anything less than that gives lower mpg. Note that 48 mph (in my 335d) is 1200 rpm, which is the minimum rpm that maximum torque is available - it's similar for 335i. You want max torque as that's essentially where the engine is able to supply enough to maintain speed.

Wind (air resistance) makes a lot of difference. Driving cross state (WA), the wind is almost always from the west. I usually get a couple more mpg going east with the wind than east into it.

Hills don't make as much overall difference, as you regain the energy (mpg) going down the other side of the pass what you lose going up. For instance, in crossing WA state from Seattle to Pullman, max mpg (going east) is usually at Crab Creek (near Othello): the low spot of the overall trip (yeah, the Columbia River is actually lower, but you have to go back up after crossing it ...)

[STR8-6IX]

Originally Posted by hassmaschine

65 seems to be peak for my 330i - that said,it doesn't really seem to make much difference if I'm going 55 or 80, on long highway runs it still averages about 33mpg.

Since all E9x's are basically 3.0 liters (in the US anyway) and have the same areodynamics, I wouldn't expect it to vary much. The primary difference will be gearing and AT vs MT. The 330i mt for example has relatively long gears compared to other models.

this is what I wanted to say.

going 80 doesnt seem to be any less efficient then 60. I believe it is because theres more torque at 2.5k rpm which helps the engine hold speed more easily

[Eddien123]

Originally Posted by floydarogers

Lots of good answers in this thread; I like this summary.

My 335d doesn't get into 6th until 48mph; anything less than that gives lower mpg. Note that 48 mph (in my 335d) is 1200 rpm, which is the minimum rpm that maximum torque is available - it's similar for 335i. You want max torque as that's essentially where the engine is able to supply enough to maintain speed.

Wind (air resistance) makes a lot of difference. Driving cross state (WA), the wind is almost always from the west. I usually get a couple more mpg going east with the wind than east into it.

Hills don't make as much overall difference, as you regain the energy (mpg) going down the other side of the pass what you lose going up. For instance, in crossing WA state from Seattle to Pullman, max mpg (going east) is usually at Crab Creek (near Othello): the low spot of the overall trip (yeah, the Columbia River is actually lower, but you have to go back up after crossing it ...)

Yes the hill thing is a good point. I used to live in south jersey where it's all generally flat. Now in north jersey there is much more elevation change. My drive to the gym is down hill and I quite literally see 45+ mpg. Obviously this isn't an accurate representation of the average MPG I'd see but it's still funny to see. Except my ride back is about 15 mpg but let's not discuss that lol

[AWSAWS]

On a flat road at a constant 50 I can see 40mpgs from my 335i with 7th gear (dct)
Still done 30mpg with a great deal of time spent at 100 though. You have to factor what your time is worth

[Welcome to NBA Jam]

http://www.afdc.energy.gov/data/mobile/10312

Answer: 55mph for gas, 45mph for diesel and hybrid.

[floydarogers]

Originally Posted by Welcome to NBA Jam

http://www.afdc.energy.gov/data/mobile/10312

Answer: 55mph for gas, 45mph for diesel and hybrid.

One can see how much this subject needs "it depends". As I noted, the 335d (and actually my wife's 328d) doesn't get into 6th until 48 mph. Not being in the top gear torpedoes MPG in general.

[335udm]

Originally Posted by natedog7700

At what speed does the MPG begin to drop on the freeway? I would like to know for 335i's because i have one but if anyone knows for a different model please share!

Why are you asking this question? You, according to your notation, are driving blown 500 + bhp 335i. Are you concerned about range between fill-ups, or cost of gas?

FURTHER: what is your experience mpg driving at different speeds? Give us material we can discuss. Thanks,

[natedog7700]

Originally Posted by 335udm

Why are you asking this question? You, according to your notation, are driving blown 500 + bhp 335i. Are you concerned about range between fill-ups, or cost of gas?

FURTHER: what is your experience mpg driving at different speeds? Give us material we can discuss. Thanks,

1) No
2) I have not cared enough, thats why im asking the forum smart one.

[natedog7700]

Originally Posted by mweisdorfer

I have got 30.5 miles per hour with my n54 going mostly 80mph on a hwy trip of 500 miles. maybe 60 of those miles were at 60mph because I was in a 55 zone.

Thats pretty good! I usually cruise 80 ish on the freeway.

[natedog7700]

Originally Posted by STR8-6IX

this is what I wanted to say.

going 80 doesnt seem to be any less efficient then 60. I believe it is because theres more torque at 2.5k rpm which helps the engine hold speed more easily

Yeah i hope not at least lol i think im churning around 2.75k rpm though at 80mph.

[natedog7700]

Originally Posted by Roma_335i

On my 335 is about 55mph.

What does it average at 55? 35mpg?