11-06-2008, 04:55 PM
|
#1 (permalink)
|
Batman Junior
Join Date: Nov 2007
Location: 1000 Islands, Ontario, Canada
Posts: 22,530
Thanks: 4,078
Thanked 6,978 Times in 3,613 Posts
|
Is VW lying to the EPA? Why does Jetta sedan / wagon have identical MPG ratings?
I was under the impression that the EPA took aerodynamic parameters into account in the final calculations for their dyno-based fuel economy testing/simulation. (Of course, can't find the link at the moment...) Or rather, that the automakers took it into account when providing data to the EPA based on their test procedures.
So why then would the presumably heavier as well as less aerodynamic 2009 Jetta Sportwagen with its likely higher Cd and (slightly) more frontal area (standard roof rails) have an identical fuel consumption rating as the Jetta sedan equipped with the same drivetrain?
I find it difficult to believe that the actual fuel consumption isn't at least 2.4% different (2.4%=1 mpg from the 41 mpg hwy rating for the TDI M-6) between these two vehicles.
Yet the cars' ratings are identical for every powertrain variation.
I don't buy it.
|
|
|
Today
|
|
|
Other popular topics in this forum...
|
|
|
11-06-2008, 05:23 PM
|
#2 (permalink)
|
Administrator
Join Date: Dec 2007
Location: Germantown, WI
Posts: 11,203
Thanks: 2,501
Thanked 2,587 Times in 1,554 Posts
|
This has been brought up a few times. Either the EPA doesn't account for aero, or it doesn't account for it enough to make a noticable difference. I'd like a solid answer on this too.
|
|
|
11-06-2008, 05:50 PM
|
#3 (permalink)
|
Depends on the Day
Join Date: Nov 2007
Location: Kansas City Area
Posts: 1,761
Thanks: 31
Thanked 41 Times in 35 Posts
|
Since they can't test every vehicle, they test similar engine/transmission combos of similar models and make an "Estimate" -- despite the added weight and different aero of the wagon.
Attached is the raw data file for '09 as a reference (several years can be downloaded directly from the EPA)...
-Rick
__________________
“If we knew what we were doing, it wouldn't be called research” ― Albert Einstein
_
_
|
|
|
11-06-2008, 06:10 PM
|
#5 (permalink)
|
Master EcoModder
Join Date: Jun 2008
Location: Northwest Lower Michigan
Posts: 1,006
Thanks: 8
Thanked 17 Times in 16 Posts
|
Nothing new. They did that for my 20 yr old cars too. They rated the sedan and wagon the same mpg, even though the wagon is about 300-400 lbs more and every one of these wagons Ive seen has a roof rack. They also rated the Pontiac 1 mpg better than the Chevy, even though they are identical powertrains, electronics, and 99% identical sheetmetal.
__________________
Winter daily driver, parked most days right now
Summer daily driver
|
|
|
11-06-2008, 06:17 PM
|
#6 (permalink)
|
Banned
Join Date: Feb 2008
Location: california
Posts: 1,329
Thanks: 24
Thanked 161 Times in 107 Posts
|
Quote:
Originally Posted by wagonman76
Nothing new. They did that for my 20 yr old cars too. They rated the sedan and wagon the same mpg, even though the wagon is about 300-400 lbs more and every one of these wagons Ive seen has a roof rack. They also rated the Pontiac 1 mpg better than the Chevy, even though they are identical powertrains, electronics, and 99% identical sheetmetal.
|
I owned a Chevy Celebrity wagon. It is not 300-400lb heavier than a sedan. The A body sedans and wagons had near identical weight.
|
|
|
11-06-2008, 07:42 PM
|
#7 (permalink)
|
MechE
Join Date: Dec 2007
Location: Bay Area
Posts: 1,151
Thanks: 0
Thanked 22 Times in 18 Posts
|
Round off error in published figures?
for example...
Sedan has a cD of .305
Wagon has a cD of .314
So published figure is .31, for both - despite the 9 point difference?
That still doesn't explain EPA figures - I would hope they use at least three decimal places... And there's no excuse for bigger FA
---
Quote:
Since they can't test every vehicle, they test similar engine/transmission combos of similar models and make an "Estimate" -- despite the added weight and different aero of the wagon.
|
Or that makes sense
__________________
Cars have not created a new problem. They merely made more urgent the necessity to solve existing ones.
|
|
|
11-06-2008, 07:57 PM
|
#8 (permalink)
|
Batman Junior
Join Date: Nov 2007
Location: 1000 Islands, Ontario, Canada
Posts: 22,530
Thanks: 4,078
Thanked 6,978 Times in 3,613 Posts
|
Quote:
Originally Posted by tjts1
What extra weight?
2009 Volkswagen Jetta wagon = 3228 lbs
2009 Volkswagen Jetta sedan = 3230 lbs
|
Whoops! That was a bald faced assumption on my part. (That'll learn me.)
I'm skeptical about the identical Cd though (and/or inclined to believe trebuchet's idea). VW USA shows Cd of .31 for the sedan, but "TBD" for the wagon.
|
|
|
11-06-2008, 09:58 PM
|
#9 (permalink)
|
Master EcoModder
Join Date: Jan 2008
Location: Mirabel, QC
Posts: 1,672
Thanks: 35
Thanked 86 Times in 57 Posts
|
I'm skeptical about the Cds too. I'm sorry but that's highly unlikely, unless the flow never reattaches to the trunk on the sedan.
Treb, I would really be grateful if you could provide a souce for those numbers!
|
|
|
11-06-2008, 10:05 PM
|
#10 (permalink)
|
Depends on the Day
Join Date: Nov 2007
Location: Kansas City Area
Posts: 1,761
Thanks: 31
Thanked 41 Times in 35 Posts
|
Quote:
Originally Posted by MetroMPG
Whoops! That was a bald faced assumption on my part. (That'll learn me.)
|
Yeah, same here -- I made the same mistake. Older wagons traditionally weighed more.
-Rick
__________________
“If we knew what we were doing, it wouldn't be called research” ― Albert Einstein
_
_
|
|
|
|