What can you do to lower drag coefficient?

 

10 Surefire Ways to Lower Drag
by Don Terrill - Racing Secrets: Auto Racing Tech ©2003
1.) Wheel Alignment – Don’t think it’s that big a deal? Tell that to the Soap Box Derby racers. They go to great lengths to make sure their tires roll without any unnecessary drag.

2.) Inflate Tires – Most racers would find, if they tested it, they would go faster with more tire pressure. I say, just keep inflating the tires until the car slows down. Try it. I think you’ll be surprised how high you can go.

3.) Choose an Aerodynamic Car – Why fight it? If you can choose any car you want, why choose a ’57 Chevy when you could choose a late model Firebird?

4.) Stop Air from Going Under Car – There’s two ways to accomplish this, lower the car and/or the use of a front spoiler. It is aerodynamically possible to get a car too low, but 90% of racecars don’t have this problem and could benefit from lowering.

5.) Limit and Release Air from Engine Compartment – Think about the amount of air that goes through the radiator and how much drag is associated with it exiting the engine compartment. The quickest fix is to limit the amount of air entering the grill – have you heard of 200mph tape?

6.) Smooth Undercarriage – For air that does go under the car, it’s best to give it a smooth path to exit the rear of the car. The use of a belly pan is the preferred method. They can be made from plastic or aluminum sheets. Watch the exhaust if you use plastic.

7.) Lower/Remove Rear Spoiler – Most race cars that have a rear spoiler, have it there because it helps them go faster, but there are still many car owners that have no idea if their spoiler is helping or hurting – test it and find out.

8.) Harder/Stiffer Tires – The harder the compound and the stiffer the sidewall of the tire, the less the drag. Now, there’s obviously a trade off between traction and drag, but as I’ve said before, test it!

9.) Synthetic Oils and Greases – This is something you don’t need to test, if you switch over every lubricant in your car to synthetic, you’re going to go faster – no question. Your engine, trans, rear-end and wheel bearings will thank you.

10.) Less Steering Movement – There are three penalties for unnecessary steering movement: (1) You’re taking the long way around/down the track. (2) Increased tire friction. (3) Power used to lift the front end – every time you time turn the wheels, the front end is actually lifted, search the web for articles on caster to learn more.

 

Cover the car in butter.

 

ROTFLMAO! That is just wrong funny

 

Thanks. The Crossfire is at .37 Cd. I am trying to go for around a .30

 

good info here.
Browser Warning

edit: I don't know why it says warning, but autospeed is a great resource.

 

One issue with the Crossfire air flow is the retro design of the rear. According to Eric Stoddard the spoiler was installed to reduce the induced lift. That suggests a significant aerodynammic negative force on the vehicle'smovement thru the air.

I'm gonna go out on a limb here and also suggest the Roadster has this issue more than the coupe.

I would think the compressed air coming under the car could be utilized to throw air and salt spray up on the back bumper. And thereby reduce the low pressure hole created at the back of the car.
Is there any advantage to using a diffuser baffle? High or low?

I would think Woody would have some interesting and likely useful ideas on this. How about it Woody?


roadster with a stick

 

I may be off base here, as I know very little about drag coefficients, but I remember reading that the XF had a lower Cd than a Jeep Cherokee so I did a little checking, it appears that a Cadillac Escalade Hybrid has a Cd of .36 and a Koenigsegg CCX supercar has a Cd of .3

Based on this, I think you would need some SERIOUS sheet metal redesign work to lower it that much, or a new body

 

Compressed air = ram air, let's not go there again.

 

you'd need a wind tunnel & major measuring equipment to accurately measure a redone crossfires drag coefficient. I'm quite sure that Chrysler when designing the crossfire used every possible trick to keep the car as slick as possible.

I'd say to get rid of xtra weight to make the car faster. That's your best bet.

 

Agreed. But the air under the car is higher pressure than that going over the car causing lift as well as drag. I'm just suggesting one could divert it into the low pressure space behind the Crossie's big butt.

Duct taping a garage door gasket to the front lip helps reduce this. I see it done on Mustangs and ricers all the time. It adds as much improvement as the best flame stickers available.

No air scope required.

 

Reducing weight only affects acceleration, not top speed. I wonder what kind of drag gains I would get from a 2 inch drop, front and rear, and an SRT front bumper with lip. And whats this about a garage door gasket?

 

Not that I'm biased or anything, but the single biggest thing you can do to drop resistance is lower the car.

The underside is already relatively smooth. The only area to smooth out is the tunnel that hides the exhaust and driveshaft, and closing that in would turn the area into a furnace.

The Corvette boasts an amazingly low coefficient of drag, and it's a result of very low ride height and a small frontal area. We can't really reduce the height of our car's face, but a bumper that extends out a slight amount at the bottom would create more of a wedge than a wall.

All I know is since I've lowered the car, I've gained a consistent 2mpg. Can't be imagining that.

 

So basically your talking about a ground effects kit to reduce the space between the bottom of the car & the road.

here's what i've found:

2006 Chrysler Crossfire Body Kits - Ground Effects

I think the srt-6's have this built in already.

 

Yes, the SRT's have a one inch lip below the original shape of the NA front air dam.

JHMK2 has it right. Lower the car.

While I was just ribbing about the "garage door gasket" I have seen it done often.
You can buy it at any Big Box home improvement center. It is Black so it hardly shows. You can mount it with tape or adhesives and replace it if you mess it up with road rash or parking lot concrete wheel stops.

I have done this myself on another car using the vinyl baseboard Coping strips. But they come in 4 foot lengths.

Very inexpensive. And cost little to keep fresh.

Hardly noticeable, it generally looks good. or at least, not tacky.

But the guys here will rib you for it.

If you are serious, lower the car. Several threads here on it. Then use this gasket to further close the front air dam to the ground.
Side skirts might also be an option, but pricey.




roadster with a stick

 

The Title 'How can you lower wind resistance?' made me think of suggesting you go commando.
Now I see that's not what you are after, sorry.

 

Does anybody have a guess as to what kind of drop in CdA we would be looking at with an all-wheel 2 inch drop? Man, I wish that somebody would make an SLR or other Mercedes style front body kit that extended forward and was more knife-edge rather than a wall. Show of hands, who would buy that?

 

Tech, if ya think back, a few months ago somebody sold a Crossfire on EBAY (or maybe Craigslist) with a newer SLK nose grafted on it. On a whole, I don't think it was very well received by the Forum.
Anyway, an SLK is supposed to have a .34 Cd, so maybe that's someplace for you start.
Keeping your spoiler down is another way to make it more aerodynamic, less parasitic drag (just stay below 90 mph). I gained better than 2 mpg by keeping mine down. It isn't why I keep mine down, but the extra MPG is a bonus.
Use skinny tires, like the old 2003 SLK's used. What you lose in handling, you'll make up in the 1/4 mile, .34sec. quicker. Less rotating mass.

 

I wish that one of these mod companies like Needswings or TVT would make such a thing in a bolt on kit. My goal is .30 Cd.

 

Im curious as to the 90 mph limit?

Good news about the positive effects of a front lip extender. At my job I see all sorts of parts getting thrown out that could be modified into just about anything. Going to keep an eye out for a "break away" lip extender