VQuick

iTrader: (17)

The coefficient of drag (Cd)* of the 4th generation Maxima is 0.32 per Nissan specs. This always seemed a bit high to me considering the aerodynamic look of the car. I'm wondering if it's high because of the stock springs being so damn tall, resulting in 7+ inches of airspace under the car, which would create more turbulance than, say, only 5 inches of airspace. Of course you'd need a complex physics model to figure out details but I think my premise is plausible. Does anyone think that a lowered Max would have a significantly lower coefficient of drag than a stock Max?

I'm also wondering about the SE spoiler and a basic, well-designed body kit such as the Stillen kit. I'm guessing the spoiler has a very slight effect at high speeds, and the kit perhaps more of an effect. Anybody care to speculate or elucidate here?



* Sprint, you should turn the [subscript] vbcode on.

mm347

iTrader: (2)

Conceivably the factory spoiler does add some downforce effect at higher speeds but I doubt that it's significant. The Stillen kit and others are primarily cosmetic and were developed for that purpose (adding style).

Lowering a vehicle should aid in reducing Cd but underbody construction (e.g. diffusers) plays the principal role in reducing turbulance and creating downforce.
Many premium German sedans and sports cars have some form of underbody aerodynamic tuning (e.g. Mercedes E class) due to high velocities that these vehicles reach on the Autobahn and therefore must have stability and certain level of control at those speeds. Maximas on the other hand (especially the 4th gen) were conceived as family vehicles which rarely would see speeds above 100mph and the engineers probably figured that such "luxuries" as proper aerodynamics are not necessary. Besides, it was a time of economic crisis at Nissan and the marketing (or whatever else) dept. employed as many cost-cutting techninques as possible.

Broaner

iTrader: (10)

I've been thinking about this for a while Tom. Its good you brought this up. .32 does seem fairly high in comparison. But the sleek look doesn't always mean the air sees it as sleek. The abrupt and totally vertical rear has a lot to do with it I think. My intuition tells me the lowering would do something to reduce drag. Sadly, I also think that on a lowered car the air going under the bumper is being compressed more thus creating even less downforce. As for the spoiler, that is only there for looks and maybe to increase gas mileage. I think any body kit is going to add more drag than downforce. If it does add downforce it will be by chance. We know d@mn well these companies don't do wind tunnel testing on their kits.

96explorerxlt

I remember in my fluids class we studied boundary layers and the fact that it just cuts off sharply should have something to do with the way the air is flowing, creating more drag. The air would be flowing up over the windshield and then down the back and off the trunk, and since theres a pressure difference, vortex's should form on the rear. This might be a bad explanation, but I remember my professor using a truck, and a tonnau as an example for something similar

VQuick

iTrader: (17)

True, we do have a blocky flat trunk, but most sedans have something similar.

I don't get what you mean about air going under the bumper on a lowered car being compressed more. Less air will be going under the car if it's lowered so I don't think it would be compressed more. Also, I wasn't aware that (real) body kits were supposed to produce downforce; I thought they were just a skirt to block some air from going under the car. The front lip if shaped properly (angled like a spoiler) might produce some downforce, true.

Micah95GLE

Lowering a vehicle generally increases downforce because the air flowing under the car is at a higher speed and lower pressure than the air flowing over the top of the car. The higher pressure above the car pushes down on the car, increasing the downforce. That's why most road-course race cars have a ride height of 60mm or less. Of course, purpose-built race cars usually have flat undertrays to smooth airflow and aid the venturi effect (this is also true of the wingless Ferrari Enzo). Another aid in aerodynamics is an underbody difuser that smooths the air flow as it exits from underneath the car. This should be designed to work with the rear wing so that the air streams from above and below the car will meet with the least amount of turbulence. With the Maxima's flat rear end, there will always be separation directly behind the car, which will increase drag.

As far as aerokits on the front, a splitter can be designed to increase downforce without increasing drag, and it has been proven that aerodynamic aids can significantly increase downforce on the front wheels at speeds as low as 40 mph. So a properly designed aero package could be useful on a daily-driven Maxima, rather than being merely decorational.

With a Maxima being a FWD car, the best solution for handling would be a high-downforce splitter on the front to increase front grip, working in conjunction with the lowered ride height and other suspension mods. Developing a package for the entire car to suit high speeds would be a hefty task, considering its un-aerodynamic underside and rear end.

Another thing to keep in mind is that most lowered Maximas have wider tires, which increase the frontal area and increase drag at high speeds. But that is a trade-off for better handling.

mzmtg

iTrader: (11)

In the grand scheme of things, a 0.32 Cd is not bad at all. There are only a handful of cars below 0.30.

http://www.teknett.com/pwp/drmayf/tbls.htm

Micah95GLE

That list is all older cars. Well, the 4th-gen Maxima is old, too. But many of the current crop of cars have lower Cd values. The G35c and some Mercedes Benz sedans come to mind, in the .27-.29 range. But I guess that's progress. The Porsche 996 had a Cd of .32.

Broaner

iTrader: (10)

I guess I was wrong on that. Micah clarified that. I haven't done the fluid motion/air resistance stuff yet in Physics. I figured that the air being forced downward by the bumper would be forced under the car creating lift.

I can't believe the G35 has a low Cd. That thing has a huge vertical rear also.

mzmtg

iTrader: (11)

The high, squared off rear ends on cars these days reduce drag. Your most aerodynamic cars on the road these days have the sharp rear cutoff: LS430, G35, Corvette (C5 & C6) etc...

VQdriver

i think it has to do with the details of the bumper, roof, rear decklid. my buddy's IS300 has a cd of .29 i think. the reason being is the front bumper doesn't have the slits our maximas have. the roofline also has a purposebuilt gutter on the both sides that looks to aid in airflow. lastly, the rear has a small decklid spoiler which probably aids in calming turbulence. all in all, we're not doing so bad. imagine what the WRX nets with the giant hoodscoop and tall, boxy stance.

BEJAY1

iTrader: (19)

Great link. I had never seen frontal area's for plugging into dataloggers!

VQuick

iTrader: (17)

Thanks for your very informative post, Micah, and everyone else too...keep 'em coming, this is interesting stuff.

VQuick

iTrader: (17)

The IS300....inferior in many respects to the Maxima (chief of which is bang for the buck!) and yet superior to the Max in so many other respects.... Hopefully I'll have a decent job in a few years so I can afford a IS350 or IS420 or whatever it ends up being.

Yeah, I think there are only a few basic rules of thumb when designing a car for aerodynamic efficiency; otherwise it's a question of fine tuning. Two cars with big squareish trunks can have vastly different Cd because the body of one was wind-tunnel tested and finely adjusted to minimize vortices and turblence etc, and the other wasn't...