Do holes in your rear bumper really make you faster?


_JT

Moderator
Staff member
Donator
Joined
Nov 1, 2008
Messages
3,546
Can you do a run without the bumper?
1.) Not sure how German police would react
2.) It has already costed me more than 50 euro's of petrol :(

So no I'm afraid...
 

  • Like
Reactions: CAL

Kozy

Bench Racer
Vendor
Joined
Aug 18, 2008
Messages
4,085
If you ever fancy doing another few runs, another experiment would be to accelerate gently to a set speed, say 180kmh, and time how long it takes to coast to a standstill.

I believe this would provide an even better insight to the amount of aerodynamic drag the rear bumper produces, as there will be less variables involed when the engine is taken out of the equation.
 


_JT

Moderator
Staff member
Donator
Joined
Nov 1, 2008
Messages
3,546
If you ever fancy doing another few runs, another experiment would be to accelerate gently to a set speed, say 180kmh, and time how long it takes to coast to a standstill.

I believe this would provide an even better insight to the amount of aerodynamic drag the rear bumper produces, as there will be less variables involed when the engine is taken out of the equation.
I know no place where I can accelerate to 180 and then stand still :p If I do that on the autobahn, I might as well shoot myself through the head, same effect only there will be something of my body left :D
 

Last edited:

Kozy

Bench Racer
Vendor
Joined
Aug 18, 2008
Messages
4,085
I did think this could be a problem! I am simply relaying an idea bought up on another forum where this discussion was being had!
 


Ben_Andersonâ„¢

B18C4 CIVIC â„¢
Donator
Joined
Jul 17, 2008
Messages
547
JT your a legend !

I allways wanted to find out by how much this affected the cars topspeed etc.

Well done mate rep added !
 


_JT

Moderator
Staff member
Donator
Joined
Nov 1, 2008
Messages
3,546
I did think this could be a problem! I am simply relaying an idea bought up on another forum where this discussion was being had!
I'll keep it in mind if I ever get on the dragstrip or something :)
JT your a legend !

I allways wanted to find out by how much this affected the cars topspeed etc.

Well done mate rep added !
lol, thanks dude :D
 


_JT

Moderator
Staff member
Donator
Joined
Nov 1, 2008
Messages
3,546
So, here are the promised graphs.

First off, the gforce graph. Clearly there is a difference. As you can see, the relative difference becomes bigger after speed increases. That's logical. Air resitance multiplies squarely (not sure how to put it in english but twice the speed is 4 times the resistance, three times the speed is 9 times the resistance etc). Higher speed = higher air resistance, higher air resistance = more profit of lowered air resistance from the car itself. Also notice that it even makes a difference in second gear.


Here's the speed graph. It tells the same as the gforce graph. It's even better visible that the higher the speed, the bigger the difference.


Just for comparison, what kinda power you would need to reach the same results :p


It ain't much but it's a cheap mod for a track car or someone that doesn't give a rats ass about the looks of his/her car :D
 


_JT

Moderator
Staff member
Donator
Joined
Nov 1, 2008
Messages
3,546
Everyone is so overwhelmed that everyone doesn't know what to say anymore? :p
 




EastCoastCTRx

New Member
Joined
May 2, 2009
Messages
22
Very good job man I just spent most of my lunch break reading this post n I dont even care.. Really good work with numbers to back it.. Major kudos..
 


WAZ-4169

fcuk ur 16 astra!!!
Joined
Dec 1, 2008
Messages
765
where did you get the G-tech thing? looks like a real handy thing to have.

great thread btw.:clap:
 


_JT

Moderator
Staff member
Donator
Joined
Nov 1, 2008
Messages
3,546
Sorry for the late reply. I got it from Ebay. It's actually like a mobile dyno and if you have a good estimate of your weight or have your car weighed, then the dyno figures aren't far off from regular dyno's. Great tool to find out what mods do to your car and learn from it.
 


andy:

EK9 type-r
Joined
Nov 6, 2009
Messages
208
nice write-up man, although i don't think i'll be drilling holes to my bodywork......:p
 


tama666

VIP Member
VIP Member
Joined
Jul 24, 2009
Messages
6,303
This is a thread worth reading a few times...thank you everyone! Thank you _JT!
 

Last edited:

boro_andy

Member
Joined
Feb 27, 2009
Messages
747
3.5 seconds quicker to 180 and half a second quicker from 100-140 that's some impressive numbers.

Based on those numbers you could estimate perhaps a good couple of seconds off your lap times. How much does it cost f1 teams to do that?

Interestingly it's slower from a standing start but then were only comparing two samples.

Good work though dude
 


_JT

Moderator
Staff member
Donator
Joined
Nov 1, 2008
Messages
3,546
Thanks :)

If you look at the gforce graph you can see it's faster with the holes :)
 




rushy_23

Member
Joined
Aug 24, 2009
Messages
121
Nice work, it is unfortunate that a test couldnt be had without a bumper, as that may have provided more increases in top end. But hats off to you going through the hassle of this.

The discussion about aero being less important at low speeds makes perfect sense, "parachuting" will be last of an impact at lower speeds, it only when you hit top end that forces become strong enough to warrant the aero Look at the increase in performance, its negligible, if the car could hit say 300km/h Im sure the increase would have been greater between bumper hole / no bumper holes.
Its all relative as they say.
 


Top