Fiat 500 Forum banner

500e Aerodynamic Drag Reduction

10K views 54 replies 10 participants last post by  500e*clipse 
#1 · (Edited)
...just by being 2" lower... at 75mph I was averaging 4.3mile/kWh vs usual 3.8 at that speed... I’m trying to find out if light wheels that are non-aero outweigh the difference between an aero wheel that’s heavier. Decisions decisions... I want to buy the Avanti Storms 10.9lb wheel but been reading they might each up the range more then gain...
That's about 12% more range! (from 3.8 to 4.3mi/kWh) Also better acceleration (0-60, 30-50, 50-80, quarter mile, etc.) since all or half of each of those is above 30mph where aerodynamics get increasingly important.

When I got Advanti Storms & 205s there was no measurable range difference. My route is slower though, with the highest speed limit at 50mph. That means my wheels' extra aero drag makes less difference than it would at 75, & my stop&go means their light weight gives a greater advantage.

If someone can tell us what they get at stock height at 60mph, we could compare to my stock-height 2013's power use with Advanti Storms in 205s, which now shows 11kW on the display at 60mph on a smooth, flat, dry, level, calm road.

The only other aero thread I've seen is the rear "diffuser", which is also supposed to give a substantial improvement, especially at higher speeds (where ANY aero improvement shows most).
 
#52 ·
So, twinturboz - any updates?

When I first got coilovers, I lowered the car to ~ 3" ground clearance. To make sure I could get up driveways, etc I cut the rubber air dam in the middle, leaving "air deflectors" in front of the FF wheels. This all worked well - ride quality definitely improved. However, there were too many issues w/ scraping the bottom. I eventually relented and raised it back up to ~ 4" ground clearance.
BTW, I noticed that the battery is not even with the rocker panels as a "bottom of car" reference. I found that the battery is lower in the back (unfortunately) relative to the rocker panels. It's very important that the bottom of the car - especially when it gets a full bottom cover - is flat or is lower in front. Otherwise you're looking at aerodynamic lift.
 
#54 ·
I've completed building a flat bottom and diffuser. Right now the diffuser angle is set at 13 degrees, a maximum determined by the rear bumper.
Here's a rearview pic of the diffuser and car bottom: The build thread is here: post # 18
Automotive parking light Tire Wheel Automotive tail & brake light Hood


Since I don't have access to a wind tunnel and smoke, I went with the "dusty road" option to visualize flow. Both live tests and examination of the dust deposits were used.
The first test was a drive-by at about 30mph:
These tests reveal a pretty small wake, considering this is essentially a "squareback" car. I'm not sure the smooth bottom contributed to this, but I do have to give credit to the folks who worked on the hatch extension, which seems to be quite effective.
Tire Wheel Car Land vehicle Vehicle


Also note the dust billowing out around the rear wheel. I did cover most of the holes in the rear fenderwells, so this is air stirred up by the front & rear wheels on this side.
This is also the best illustration of how the wake, which is only half of the cars height, follows in the back.
Wheel Car Tire Land vehicle Vehicle


Another driveby at 20mph showed mostly clean air in the middle with the dust following the wheels.
Wheel Tire Car Vehicle Automotive tire


Yet another shot shows something mostly talked about, but rarely photographed. :D For example, in "Race Car Aerodynamics, Designing for Speed" by Joseph Katz, there is an illustration (Fig. 6-36) on page 221 showing vortices created by venturies and underbody channels. These vortices are created by air being pulled in sideways by the low pressure in the diffuser, and are actually a good thing because they help keep the air attached inside the diffuser. I was shocked to actually be able to get a picture of this!
Wheel Tire Car Vehicle Automotive tire
 
#55 · (Edited)
After the tests, I looked at where the car was dirty. The car was washed & completely clean before the test. Generally, turbulent air will cause dust to deposit on a surface, while free flowing air won't. You can see a light dust deposit on the side behind the front fender, following for about 12". This dust is at the height of the tire/rim. This is pretty common and would be worse if cooling air flowed through the front fender. It's also heavily deposited on the rocker panel.
Wheel Tire Land vehicle Vehicle Car


Underneath, you can see dust deposited directly behind the front tire. The middle area of the bottom is clean.
Tire Automotive tire Hood Wheel Vehicle


Here is the diffuser after the test. I've circled a few spots for illustration. The sides of the diffuser (red circle) had pretty heavy dust deposits. This makes sense, given the amount of dust billowing around the rear wheels and the low pressure air in the diffuser pulling the dirty air in, creating vortices that would then deposit the dust on the sides. whew!
The yellow circle shows a light deposit of dust, probably caused by a discontinuous region in the diffuser. Since the diffuser angle is a bit steep, this area is borderline.
The green circles show the dust patterns around the fasteners. Notice they all follow straight behind the bolts. If the air in the diffuser was disconnected or even flowing backwards like the diffuser on that Lotus in the end of post #16, (of the build thread) these dust deposits would have been on the opposite side.
Generally, even thought the angle is currently set steep at 13 degrees, it appear that the diffuser is working properly.
Tire Wheel Automotive tire Tread Hood
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top