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Braingears
Expert
Date registered: Apr 2006
Location: St Petersburg, FL
Vehicle(s): G320 & ML320
Posts: 1450
| Aero Dynamics
Everyone always comments on the aero dynamics of the G-Wagon. I have always found it curious how the Sprinter is a larger and taller vehicle and is able to get better fuel economy, perhaps with the same engine. I personally think that the additional 4x4 gears, both the transfer case and front differential, is where the power loss and loss of fuel economy occurs. I also think, especially on mine, that gearing is a little low too. At 80mph, my engine is running at 4000rpm, and that is not the most efficient engine rpm. In the newer models, they have added the fifth gear. I am pretty sure this is why the G500 gets better economy than the G320. Although the G-Wagon is "boxy", the sides are for the most part a straight and flat panels. And I do not think that the front and windshield of the G-Wagon cause any more friction than most of the trucks out there. I wonder what the drag co-efficient of the G-Wagon is compared to the Sprinter Van? I found these pictures on http://www.mercedesbenzone.com/.
http://www.mercedesbenzone.com/archieve/july06/image/Mercedes-Benz_Sprinter_wins_German_Commercial_Vehicle_Prize/mb-27.jpg
http://www.mercedesbenzone.com/archieve/july06/image/Mercedes-Benz_Sprinter_wins_German_Commercial_Vehicle_Prize/mb-28.jpg 
Edited by Braingears 8/20/2006 1:27 AM
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AsianML
Date registered: Dec 1899
Location:
Vehicle(s):
| Re: Aero Dynamics
A brick could get better gas mileage than a G. 
The pics aren't working for me.....? |
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roughneck
Expert
Date registered: Apr 2006
Location: UK, Germany & USA
Vehicle(s): 270 cdi.300 GD 300 GE.lwb 300 GE.swb. Disco 2
Posts: 4398
| Re: Aero Dynamics
Any extra component that is turned by the engine or pushed through the air by it adds to fuel consumption by the very fact that it requires an energy source to do so. That goes for air con, alternator, heavy duty alternator takes more, large added lights to the front, bull bar, larger rear views, roof rack etc etc, The fact that the G is slab sided goes against good airodynamics, compressed air flow at the front and wind shield is unable to expand as it passes down the side and top of the form, finaly doing so at the back of the vehicle where it changes to suck on the back of the G, The answer is to add more energy which Mercedes continues to do without changing any of the form.
The perfect aero dynamic shape is a rain drop a form createdby air flow, I would suggest that if the aero dynamics of a g worry you then you have the wrong vehicle, as for the coeficient of drag factor it is probably around the terminal velocity of a breeze block in free fall.  |
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DUTCH
Administrator Doppelgänger
Date registered: Apr 2006
Location: US, GA, Atlanta
Vehicle(s): 2015 Audi Q7 3.0 TDI,2018 Sprinter
Posts: 9963
| "Aerodynamic Drag of Vienna's Hoffburg Palace"
A technological masterpiece with the "aerodynamic drag of Vienna's Hoffburg Palace" (DaimlerChrysler), it is still considered, practically unaltered . . . . since its introduction, the world's best off-road vehicle.
from page 49 of the book 100 Years of Steyr-Daimler-Puch Graz. |
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mark
Veteran
Date registered: Apr 2006
Location: UK
Vehicle(s): G300TD
Posts: 161
| RE: Aero Dynamics
The old sprinter had a Cd of 33 i think. I wouldn't be surprised if the G's was over Cd 50. A LWB G Wagen also weights a good 400kg + over a empty medium size Sprinter.
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ewalberg
Expert
Date registered: Apr 2006
Location: Past: San Francisco. Present: Germany
Vehicle(s): 2000 g500
Posts: 1887
| RE: Aero Dynamics
I would not underestimate the poor aerodynamics of the g-class. It's entirely reasonable that you could make a full sized big rig truck that's more aero-dynamic than a g-wagen. In fact, i think i read some articles of big rig trucks that were designed for just that purpose and they got over 20mpg with "normal" deisel motors. The affect of aerodynamics is i think the product of the square or the cube of speed... i can't remember but it makes a huge difference. and yes, we do loose something in the transfer case, other gear trains associated with full time 4x4 love. ... all things considered, i think the g-wagen is more efficient than it should be... which is perhaps more a credit to the motor and well made bearings and gears. I think the g500's are lower geared than the 320's which would make sense then why they 320's may not see a highway benefit... but the shorter gears in the 320 would make for a better driving feel and power curve for offroad/onroad benefit rather than best fuel economy. |
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hipine
Date registered: Jul 2006
Location: US, CO, Bailey
Vehicle(s): 460 1980 280GE w. 617A
| RE: Aero Dynamics
I too would not be surprised if the Sprinter had significantly better Cd than the G. It really comes back to the "design inputs" when each was conceptualized. The G was designed in the mid 70s as a military off-road vehicle. High speed and economical operation were far down the charts of desired goals to achieve. The Sprinter was designed 20 years later when there was lots more experience with arerodynamic road vehicle design, and being designed from the start to serve as a highway-plying fleet vehicle, I'd imagine that fuel economy was VERY high on the list of things to optimize, and aerodynamis high on the list of ways to do that. Not to mention weight savings. If you find Cd numbers, see if unladen weight is nearby at all. You might find a G weighs as much or more than an empty Sprinter. All the rest, operating RPM.s, gearing, etc come to serve pushing the thing through the breeze. Rolling the components in the front axle has some effect, but not nearly what's consumed in bucking the wind. -Dave G. |
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Container
Veteran
Date registered: Jul 2006
Location: Sweden
Vehicle(s): 1998 G500L, 1994 E36 AMG Coupé, 2007 E500T 4-matic
Posts: 114
| RE: Aero Dynamics
In 1975 I had a new Chevy Blazer with the 5.7 l petrol engine. It was consuming more or less exactly twice as much as my present G500, so I am pretty happy with the figures after all... |
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roughneck
Expert
Date registered: Apr 2006
Location: UK, Germany & USA
Vehicle(s): 270 cdi.300 GD 300 GE.lwb 300 GE.swb. Disco 2
Posts: 4398
| RE: Aero Dynamics
If I remember correctly, the earlyVW Beetles had a lower Cd than the Jaguar E type of the same era. The VW shape was based on a rain drop. |
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T.Schuhe
Elite Veteran
Date registered: Apr 2006
Location: Olympia, Washington State, USA
Vehicle(s): 460 1985 LWB 300GD five speed
Posts: 711
| RE: Aero Dynamics
Ze,
Your RPM observations seem correct. Many engines are set up to operate at slower speeds, but this may not be a good thing in the long run. MB engines have usually relied upon higher revs, and this seems counter intutive to me as well. I do recall as a yougth that tractors on our farm were of many brands, and the ones that were allowed to run at a steady full governored rpm (1800-2000) and were never allowed to lug down, were always longer lasting than tractors that were set up to be harder to shift down to a lower gear and were left to lug through difficult plowing areas or other tasks. I was interested in this observation and had several engineers from tractor companies explain that when an engine was allowed to lug during heavy work, that several things happened
internally: 1. fuel was not fully burned and thus inefficient in it operation - this cause the oil to become deluted and harmed engine parts; 2. the piston in the cylinder under such lugging conditions would tend to turn or cant within the cylinder wall, creating heat and wear. This lesson has stuck with me, and seems to apply to most vehicles. Freer revving engines might just last longer if cared for in all other ways.
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Braingears
Expert
Date registered: Apr 2006
Location: St Petersburg, FL
Vehicle(s): G320 & ML320
Posts: 1450
| Re: Aero Dynamics
I run the piss out of my Mercedes diesel engines. They are made to be revved out. I always tell everyone that I do not allow the carbon to build up. I blow it out every chance I get...
On my G-Wagon, I hardly ever run below 3500-4000 RPM. Even for a gas engine, that seems a little high for constant running (500-1000 miles per week). |
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amzimmy
Elite Veteran
Date registered: Apr 2006
Location: South Africa/Italy
Vehicle(s): GD300 1981, Alfa GT 3,2 V6, Alfa Brera Q4 3,2 V6.
Posts: 850
| Re: Aero Dynamics
Braingears - 8/24/2006 7:27 AM
I run the piss out of my Mercedes diesel engines. They are made to be revved out. I always tell everyone that I do not allow the carbon to build up. I blow it out every chance I get....
This is called "ITALIAN TUNE UP" it should be done at least every 400 - 500 km, choose a long stretch of road and put your foot flat down. Diesel engine like that, I do this exercise with mine too and never had any problems (odometer reading above 400 000 km)
This is part of an article about engine performance by Volvo:
"Italian Tuneup" (driving at high rpms while the engine is fully warmed up) is frequently very effective. [Caution from Zippy] Volvo specifically recommends AGAINST using any fuel or oil additives. I know they used to suggest it was okay, but then decided that catalytic converter damage is done when additives are used. Since about 1993 diesel improvements have made additives unnecessary.
amzimmy  |
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KERR
Date registered: Dec 1899
Location:
Vehicle(s):
| Re: Aero Dynamics
The other day for fun we rest my computer and drove about 15 miles on the interstate.
at 60 mph it said my average was 17.5 over the 15 miles.
at 65 mph it said my average was 15.0 over the 15 miles.
at 70 mph it said my average was 14.0 over the 15 miles.
at 75 mph it said my average was 13.0 over the same 15 miles.
Guess thats why my milage always sucks. to not get run over you need to be running at least 75 around here.
Also noticed over the last few week that our new armada suck gas in town and gets grate milage on the high way. It records 12.7 to 13.0 in town milage but if you cruise on the free way it goes way up. Our new son has kidney issues so we travel ever two weeks to the childrens hospital. Anyway the last treck down with curise set at 80 the armada got 17.8 mpg over the 100 miles. on the way back at 90-95 mph (fallowed a new 760LI bmw and a M5) it got 16.5 mpg!
I think the main problem on the G is:
1) pushing both diff's all the time
2) it needs more gears.
3) shaped like a wall. |
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Braingears
Expert
Date registered: Apr 2006
Location: St Petersburg, FL
Vehicle(s): G320 & ML320
Posts: 1450
| Re: Aero Dynamics
Although Germany and Austria have excellent highways, while I have been driving through Panama and Costa Rica, I rarely drive over 60 mph. Most of the roads are not made for it. In places like that, I'm sure that it does a lot better. |
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