cutting holes in your rear bumper

[theblackbullet]

Lately I've come across some drag cars that have cut holes in their rear bumpers. They justify the action by saying that it allows air to escape from the rear bumper and helps prevent the parachute effect. I have seen claims of people dropping anywhere from .1-.4 seconds off of their 1/4 mile. I personally drive over 300 miles a week on the interstate, and if this could help me at all, Id like to give it a try.

Has anyone done any testing to prove this an effective technique?
Does anyone have the knowledge to explain to me why it wouldn't be effective?

worst case scenario, I will find an extra bumper to experiment with myself.

here is what I am talking about...

[ldjessee00]

Hello,

I would be concerned that your insurance company would use it as an excuse not to pay a claim, saying you damaged safety equipment.

Why not just enclose the underside?

[theblackbullet]

Originally Posted by ldjessee00

Hello,

I would be concerned that your insurance company would use it as an excuse not to pay a claim, saying you damaged safety equipment.

Why not just enclose the underside?

The holes wouldn't actually be in the bumper. just in the thin plastic cover
it wouldnt make a difference in the structural integrity of the car

mostly just because this would be easier for the time being. Im lazy

[Christ]

It really wouldn't be any easier than cutting a piece of cardboard for testing purposes. The claims about "Speed holes" in rearward body cladding probably aren't all they're cracked up to be, either. Imagine how little air is actually succumbing to the parachute effect, and how little air is actually under there to begin with. You're almost universally better off smoothing the flow path.

Those holes create much more turbulence, as well.

[Bicycle Bob]

It is better for air to go around than through a grille. I vote for a partial belly pan ahead of the "parachute." If I were modifying a race car, I'b be tempted to say that what didn't help did, and vice-versa, trying not to help the competition.

[Nerys]

Hmmm I am more inclined to think this INCREASES drag which for a racing car MIGHT result is more rubber on the ground in the rear which might explain the faster times.

IE worse for mpg concerns :-) Just a guess.

[Frank Lee]

Now you have me curious: How does more rubber on the ground in the rear make this car quicker???

[theblackbullet]

Originally Posted by Frank Lee

Now you have me curious: How does more rubber on the ground in the rear make this car quicker???

lol yep
civics are front wheel drive

if anything the downforce on the rear would hurt

[Sean T.]

Why not try just removing the rear bumper cover? That would be an easy way to see if it helps.

[Nerys]

thats easy frank. First MOST "racing" cars are rear wheel drive for exactly that reason Second the more force you have pushing DOWN (drag helps push down or at least STOPS some "lifting up" results the same.

the more you push down the more POWER you can "push" into your rubber without losing grip.

its one of the reasons I can DUST pretty much any sports car in the hole shot in my Cherokee. I have an ass ton of torque and enough rubber that NO amount of throttle causes me to lose traction even in the rain. SO when I hit go "I GO" while the 911 chirps his tires and loses the hole. (and then 3 seconds later blows by me like a missile of course but I have already humiliated him at that point) ie most people who have those cars have no clue how to actually handle them :-) same goes for 99% of people driving SUV's

so the more you can push down or avoid "lifting up" the rear tires the more Horse Power you can push to the wheels.

The more Horsepower you can push to the wheels the FASTER you can go in theory.

this of course assumes you have excess horsepower at your disposal and are limited by your tires ability to translate it.

It was just a guess as to why some who claimed to get better times by doing this.