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The Official Drag Coefficient of Your Brick

DefineGoodGuy

DefineGoodGuy

Kavorka
Joined
Apr 15, 2013
Location
Utah
This might be skirting off-topic territory but I found it very interesting and potentially performance related. I came across a report done by Volvo in 2012 that lists the drag coefficient for almost every Volvo since the PV. http://www.mech.kth.se/courses/5C1211/Externals_2012/Ljundberg_2012_1.pdf

Some things I pulled from the report:
-The 245 is indeed a 0.45 to the 244’s 0.47
-The P1800ES is actually the most brick-like at a whopping 0.61 (They didn’t test the C303)
-Changes to frontal area have less drastic effect on overall drag than changes to the coefficient of drag
-The 140 didn’t warrant a ranking :-(

Potential upgrades for those looking to cut down their Cd:
-Aero wheels (give me all of your global warming causing five spokes)
-Lower your car because science
-Underbody sheathing, especially to move air away from the front wheels
2455_2mg.jpg

-Functional hood scallop to increase flow through cooling components
2455_7mg.jpg

-Some sort of wing or perhaps http://jalopnik.com/5961496/make-your-car-look-like-an-evo-in-the-name-of-fuel-economy to decrease turbulence
-Buy something other than a Volvo

As an aside, I think the photo of the group that worked on the project may have been shopped. :grrr: There is no way that someone is that tall.
 
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very, VERY COOL. And a stern reminder to get my splash guard back on underneath the car, asap.

Actually noticed a difference when I lowered my car, on the hwy my rpms were lower at the same speed.
 
Karl Buchka said:
How do you support this conclusion?



Lowering your car changed the gearing?
Click to expand...


No. My car was raked in reverse, thanks to sagging nivomat suspension, and was effectively riding like a boat, nose up. Probably a good 8 inches higher out front. It was almost comical.

All that air underneath the car required me to push the pedal down further to achieve the same result.

Or does that not make sense. Automatic btw. Maybe it was just under more load and in boost more to achive the same result. Either way, WAAAYYYY less gas used when it was lowered compared to motorboating.
 
atrokz said:
No. My car was raked in reverse, thanks to sagging nivomat suspension, and was effectively riding like a boat, nose up. Probably a good 8 inches higher out front. It was almost comical.

All that air underneath the car required me to push the pedal down further to achieve the same result.

Or does that not make sense. Automatic btw. Maybe it was just under more load and in boost more to achive the same result. Either way, WAAAYYYY less gas used when it was lowered compared to motorboating.
Click to expand...

More load yes. More RPMs? Maybe if your torque converter unlocked?
 
Karl Buchka said:
How do you support this conclusion?
Click to expand...

I should have phrased that differently. According to the report, even though frontal area has risen in past years, Cd has continued to drop due to advances in aerodynamics understanding and air flow testing. When you look at the P1800 vs an XC90, it would be hard to tell how much more drag the 1800 has just based on the silhouette.
 
Cd isn't a measure of total drag, though, just a comparison of how much drag there is on the car vs. (I could be off here) a flat rectangle shaped object with the same frontal area.

You have to combine the two measurements (CD and frontal area) to arrive at the drag. Well, you have to add in a speed as well.

Thus the P1800 is no more aerodynamic than a 122 sedan was, but as a result of being smaller, and having less frontal area, it has less drag at speed than the 122 did.

It's not that surprising that the PV is so bad. It's aerodynamically 'styled' (like the 1800), but there's pretty much not a single drop of actual aerodynamic engineering on it. It has smooth flowing curves, but they're almost all on the back side, the front edges of everything are vertical or near vertical surfaces. And the air going down the sides has to fight with the rear fenders as well as the fronts.
 
PS: The 1800ES figure of .61 seems suspect. Why would it be so much worse than an 1800's .48? They're identical except for the hatchy/wagony rear greenhouse, I can't imagine why that would be so dramatically bad for aerodynamics. The 240 wagons are more aerodynamic than the sedans.
 
Extremely cool data - thank you for the additional charts. There are most certainly a few modifications that could lead to large drag reductions on the 240. While not necessarily the traditional idea of performance, it is a topic that nonetheless deserves to be in this section.

I'm surprised at the large drag numbers for the wheels and floor. Surely there must be some way to streamline flow in those areas in such a way as to increase efficiency? It seems that with an few aero inspired solutions, economy could be increased in a way that would have no impact on the aesthetics of the car - it's all underneath and unseen anyway, so who cares? Slap on a few panels and find some way to smoothly direct airflow away from the wheels, and there you go...
 
JohnMc said:
Cd isn't a measure of total drag, though, just a comparison of how much drag there is on the car vs. (I could be off here) a flat rectangle shaped object with the same frontal area.

You have to combine the two measurements (CD and frontal area) to arrive at the drag. Well, you have to add in a speed as well.

Thus the P1800 is no more aerodynamic than a 122 sedan was, but as a result of being smaller, and having less frontal area, it has less drag at speed than the 122 did.

It's not that surprising that the PV is so bad. It's aerodynamically 'styled' (like the 1800), but there's pretty much not a single drop of actual aerodynamic engineering on it. It has smooth flowing curves, but they're almost all on the back side, the front edges of everything are vertical or near vertical surfaces. And the air going down the sides has to fight with the rear fenders as well as the fronts.
Click to expand...

It's as if the C stands for coefficient.
 
JohnMc said:
Cd isn't a measure of total drag, though, just a comparison of how much drag there is on the car vs. (I could be off here) a flat rectangle shaped object with the same frontal area.

You have to combine the two measurements (CD and frontal area) to arrive at the drag. Well, you have to add in a speed as well.
Click to expand...

Right, you'd then plug in the Cd to the drag equation
99a6015b6a230860c9b1517b238e5de9.png
along with the other variables and you'd get the actual drag. Cd is just a simplified way of comparing two objects.
 
DefineGoodGuy said:
Right, you'd then plug in the Cd to the drag equation
99a6015b6a230860c9b1517b238e5de9.png
along with the other variables and you'd get the actual drag. Cd is just a simplified way of comparing two objects.
Click to expand...

Yeah, that's true. But you said that the 1800 has more drag than an XC-90. Which isn't necessarily the case. The 1800 has a lot less frontal area, it's very possible that it has less drag despite the worse Cd.
 
I see that the P2 V70 posts the lowest CD of all the cars except the S80, CD= 0.31 which I believe is due to the wheels and ground clearance.

When I bought an 2004.5 V70 2.5T the Volvo literature posted a CD of the same 0.31 for the V70, much lower than the sedan S60, and that there was a significant drop to 0.29 for the V70 when the 17" Amelthea sport wheels, sport suspension and rear spoiler was added, making it very close to a 911 Porsche of the day, which chimes in at 0.27.

When the newer body style came out in 2008 the CD increased so there was a period where Volvo's aerodynamics were nearly the best in the industry.

And CD means Co-efficient of Drag. It is a multiplier that normalizes each cars drag in an effort to make comprehensive comparisons of each cars characteristics, not to be confused with total drag itself.

The square back wagon shape is somewhat of a dual arguement of how not to make, how to make a car have less drag. A boxy square shape will have a significant vacuum behind the box as it is propelled forward. The vacuum which is created by the velocity and mass moving forward leaves a void of air space behind it, which is known to pull the car rearwards, and is a part of the equation not governed by frontal area but adds to total drag. The very interesting part of the wagon equation is that the simple introduction of a rear roof spoiler inhibits that drag force and can make the wagon shape lower CD than the same car having the same frontal area with a sloped rear facia, like the S60/V70. In the literature from Volvo the addition of a rear spoiler to an S60 makes no difference at all on CD.

The 240 I dunno, it's boxy and all wings aside it is still a drag, wagon or sedan.
 
JohnMc said:
Yeah, that's true. But you said that the 1800 has more drag than an XC-90. Which isn't necessarily the case. The 1800 has a lot less frontal area, it's very possible that it has less drag despite the worse Cd.
Click to expand...

You can see the full effect on the chart of their compound variable, CdxA (drag coefficient times frontal area).

The 1800ES is 4th in the timeline (not sure why they listed it as 1968 though) so count 4 points over from the left and you'll see that CdxA = 1.07 or thereabouts.

The XC90 is circled and CdxA = 1.09. So for the same air density and vehicle speed, the 1800ES will have about 2% less drag force in the direction of flow than the XC90 if the data is good.

Still pretty terrible, and I'm also skeptical about Cd = 0.61 as they show.
 
Duder said:
You can see the full effect on the chart of their compound variable, CdxA (drag coefficient times frontal area).

The 1800ES is 4th in the timeline (not sure why they listed it as 1968 though) so count 4 points over from the left and you'll see that CdxA = 1.07 or thereabouts.

The XC90 is circled and CdxA = 1.09. So for the same air density and vehicle speed, the 1800ES will have about 2% less drag force in the direction of flow than the XC90 if the data is good.

Still pretty terrible, and I'm also skeptical about Cd = 0.61 as they show.
Click to expand...

:nod:

Should be as good or better than the 1800 with it's semi cammback rear deck.
 
I guess it's possible that the 1800ES tail creates a huge low-pressure zone that is completely uncontrolled and accounts for Cd = 0.61. A true Kammback is closer in shape to modern hybrids like the Insight and Prius, whereas the 1800ES tail looks more rakish and stylish but probably doesn't function as a true Kamm should (reducing drag vs. an extended tail that tapers to a point).
 
vvpete said:
The square back wagon shape is somewhat of a dual arguement of how not to make, how to make a car have less drag. A boxy square shape will have a significant vacuum behind the box as it is propelled forward. The vacuum which is created by the velocity and mass moving forward leaves a void of air space behind it, which is known to pull the car rearwards, and is a part of the equation not governed by frontal area but adds to total drag. The very interesting part of the wagon equation is that the simple introduction of a rear roof spoiler inhibits that drag force and can make the wagon shape lower CD than the same car having the same frontal area with a sloped rear facia, like the S60/V70. In the literature from Volvo the addition of a rear spoiler to an S60 makes no difference at all on CD.
Click to expand...


True, but having 2 of those crappy transitions is even worse, hence the 765 is 0.05 cleaner CD than a 764
 
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