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Michael Ghia August 25th 2003 22:15

Aerodynamics of a bug
I've read the last aerodynamics post about the Ghia but what about the bug?
I'm still in the process of rebuilding my Oval with Porsche power (3.2 230bhp mid mounted) and as the car will weigh less than the 911 3.2 Carerra, it'll do more than the 150mph top speed capable from the 911.
The last time I ran my bug to 120mph, it was all over the place, the back end was very light.

VW have limited the new Beetle to 145mph, even the RSi with the spoiler which pops up above the rear window. They've also limited it in racing so there is def a problem.

I don't really want to change the body style hugely and a pop spoiler would be good but it looks like it'll have to be a huge wing to make any difference.

Anyone run their bug up to 130mph plus?


Alex August 25th 2003 22:20

How about looking at the floorpan.

I was thinking into making some venturi channels under the floorpan and getting some carbon sheets to close of the front and rear part of the car as much as I can. This way the air can not get in areas you do not want it and it will accelerate the air flow pressing the car down more on to the street.

Well this is all not know if this would really work.

Michael Ghia August 25th 2003 22:26

Floor ducting
I like the idea. As I'm going to be starting from scratch with the chassis, I may be able to incorporate something into the design.
I think the only street car which has ever made proper use of floor ducting is the Jaguar XJ220.
I may be able to fit a front spoiler under the bumper with ducting through the shell and out the back... I also need to feed the engine air so this may have a dual function.


Alex August 25th 2003 22:35

Try to find a pic of the Ferrari Enzo. I have one from Auto Motor & Sport of the floor. Extremly amazing. Totally flat with 2 venturies in the front on each side and a variable difuser in the back.

I see if I find a scanner and I will email you the pic.


Wally August 26th 2003 03:04

Re: Aerodynamics of a bug

Originally posted by Michael Ghia

Anyone run their bug up to 130mph plus?


Well, not quite that fast, but it went 117,3 mph (real, digitally clocked) with the 2 ltr and was still reasonably stable at that point.
Maybe you can also get some idea's of the car from dr. Jozef Gerold, when he last competed in the Käfer Cup series in Germany.
Doing s/th with the floor pan is still the best idea since it will not 'spoil' the looks of your Oval.

Good luck,

Chris Percival August 26th 2003 06:36

Not quite that fast either, but I run a spoiler on the track, and it makes a real difference. I know what that 'light' feeling feels like, and its not nice, but with the spoiler the rear never feels light. Couldn't tell you if the car is faster round corners with it, but it sure gives me more confidence...

Rob August 26th 2003 07:41

I read somewhere that one of the problems with the bug is that air gets trapped under the fenders.
I've seen a couple of 'race' bugs with louvres in the back of the front fenders... maybe that's something ?

This is a pretty cool thread.....I've been looking for an excuse to get me one of Carbon Joe's rear wings :D :D :D


Sandeep August 26th 2003 08:52

I've had my bug to 180-190kph ONCE ... at that speed the rear end was VERY unstable. It felt like the rear was floating. This was with 195/65/15 tires, front 3/4" swaybar and no rear swaybar. The shocks were 14yrs old.

I'd like to try this again when I install my 18" wheels and brakes. Since then, I've installed a 20mm front adjustable and 24mm rear adjustable bar but I think I won't be able to hit that speed again as the resistance from the tires will be high. I've only got a 914 2.0 and with the foot to the floor, the car would not accelerate anymore.

I like the idea of looking at the floorpans, thus keeping the body looking stock. I'm not one for huge wings but a CarbonJoe roof spoiler would look nice.

So how do you go about modding the floorpan ? I'm sure a front spoiler would work too but not sure if thats an option for a split.


DaveM August 28th 2003 15:33


I know it's not a Bug, BUT the Audi R8 has probably got a pile of airodynamic research as they do 200 mph and really want to stay attached to the race track. Remember the flying Mercedes at Le Mans a few years ago?

Anyway, there's some good photographs and interesting information at:

the first picture shows air management around the front wheel wells (note the slots on top of the bodywork above the wheels too) and another picture further down the page shows the rear diffuser.

I think the comments of some of the previous posts are correct that air under the car is as important as air over it. Clever work could build under trays but I think a diffuser would really help. And the slotted fenders talked about are shown in the "Japanese Racer" tech article. I wonder if you could make slotted fenders look good on a road car? Driving in the rain will produce some interesting spray patterns too!


Racelook August 28th 2003 17:05

Whoow... This are the topics that I like.. where i'm very interesting in....:silly:

How does the air have to move under a bug to be so optimal as possible?

I'm going to mold a aluminium spoiler (high wing)for downforce and of course for the looks.

Works holes in de fenders really???

Greetings Wiebrand

Sandeep August 28th 2003 17:19

Here's what we need to do .... does anyone have a video of a bug running down the highway with small peices of yarn taped to the car ? I saw this somewhere once (new beetle I think) and judging by the way the small pieces of yarn react, you'd have an idea of high and low pressure areas ?

I'm still unclear as to how the underpan system would work.

I thought that the reason the Porsche at Lemans a while back flipped was because of air getting under the front of the car ?


judgie August 28th 2003 17:31

have spent most of today under a lotus elise and it has a compleatly flat under try with a small venturi[?]at the rear,also 2 small naca ducts under engine/gearbox.ducting also from the grill in the front exits from the bonnet vents after flowing through the rad.worked an a exige[motorsport elise]a few weeks ago and that had vents in the back of front wings and sort of vanes directing air towards the sides and the rear venturi.also a big wing up in clean air.
i know a lotus is no bug but,you have to take ideas from any whare.
cheers rob

Vincent August 28th 2003 22:49

I just bought a 74 pan for my 64 bug and I am going to replace the floor pans with sheet metal just flat as I do not need the extra head room provided by the lower area of the floor pan. I am installing racing seats that sit low. What I am planning on doing is building 3 or 4 sections of flat sheet metal probably aluminum for weight to have a completely smooth underpan. Removing the floorpans will give me a smooth flat pan all the way back like a RC car. I am also installing a 13b Turbo rotary inback and plumbing it for the rad up front. sence my motor will not need the air to cool it I am going to inclose the bottom of the engin bay too. I am going to run some small channels in back to create a defuser ie down force. right before the transmission on each side I am going to install two naca ducts to feed the tranny with air. up front I am going to have a small spoiler to draw air to the radiator. Next installing two channels forcing air to the side for the brakes. I will also do the same in the back to direct air to the rear brakes. The front and rear sections will be removable for service on the suspenstion and engin. This should reduce drag under the car and give a bit of down force at the rear. I may go as far as cutting out part of the rear apron to create a real difuser.

chigger August 30th 2003 10:55

I have looked at this subject for quite a while. One of the problems with looking at other race cars is that the aerodynamics are often dictated by the rules and not the possibilities of the engineering. Most of that you see is the car designers ideas to get the most out of what the rules allow.
For example the vents to the rear and top of the fenders is to relieve lift in the fender wells as a result of the of the GT racers going airborne. The rules made these mandantory. They do decrease lift, but also create drag.
The flat pan is also rule mandated. It is not the best undercar design, but it is required. Since I am not rule directed I have come up with some interesting ideas.
You have to approach the aero as a package not just individual parts. The following is some of my ideas, many which are hard to explain quickly without pictures.
Closing all the air catcher holes around the front end is a start. It is good to keep air out of the box section where the steering box and MC are located. To the front of the fender a plate can be placed in the fender to keep air from getting into the fender well. The rear of the well also has a plate used to direct air out of holes in the fender at about a 45 to 60 degree angle. This would be a lot of work for limited benefit unless you are going really fast. The same applies to the rear fender well.
A front spoiler is a necessity. Sorry it just is. You can use it to keep air from under the car or to channel air to your underbody aero mods. Another mod for the front is small strakes (triangular plates set at angles to the ground) on the outside of the fenders. Effective but obvious.
A rear spoiler is a necessity also to break the rear lift. It doesn't have to be very big. The angle is important. It and the underbody difusers output should create a defined flow much like using sheet metal. If drawn it would look like a pointed tail coming off the rear of the car. The spoiler can also be used to pump a wing. In order to work properly the wing must be positioned over the ground with no car parts under it and as low as possible. This would look quite weird and work very well, maybe to well as it might lift the front end. Raising the wing until the airflow from the spoiler flows below the wing would pump the wing and perhaps create the same effect.
At the least I believe you need both a spoiler to keep air from under the front and a spoiler to break the lift in the rear. The rear spoiler is going to have to be used. Most of the rear spoilers I have looked at don't work right or they have other problems like blocking the cooling vents.
I have some really good ideas on modifying the pan which work very well. I have tested them with a model and I was impressed with the downforce and the self correcting aspect. It seemed to create more downforce if one of the ends or sides lifted causing it to bring down the raised side or end. I will have to draw up some pictures to explain it. It is quite simple to make and is totally hidden under the car.
These are some, but not all of the areas I have been investigating. I hope some of it is of help.

andy4d September 4th 2003 07:23

for some really good info, check out this site: Undertray

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