Creating a roof spoiler

Then I got the idea to use this “spoiler” as a mold to create a thinner, lighter spoiler with an edge around it. The plan is to slide the edge under the rear window rubber, the rear window rubber will hold it to the car.
Luckily I had an old rear window lying around in my barn. That was perfect for this project:

Second try...


If I now put glass fiber cloth on it, it will become a spoiler with a small edge around it. With the same shape as the rear window.

Taped it with packaging tape, so the “spoiler” will stay in place, and it will prevent sticking of the polyester resin. On the packaing tape I waxed it with bee-wax. Then I put glass fiber cloth on it, en drenched it with polyester resin using a brush.

Fiber glass cloth

There are 3 to 4 layers of glass fiber cloth on it.

After it hardened, I just had to allready test-fit it on the beetle:

Early testfit

Of course it still has to be smoothed with filler.
It’s hold on pretty tightly only using the window rubber!

After a lot of filler, sanding, filler, sanding etc, a second test fit:

Another test fit


Another test fit rearview

I like it!
The rear edge still has to be trimmed a bit, but it’s getting there.


  1. That sounds like a vortex generator , which may induce more drag than it reduces. My understanding of the roof spoiler is to provide a sharper cutoff to the airflow to reduce some of the drag caused by air partially detaching along the steeper back slope. By detaching the air completely you still have the full drag of the entire frontal area.

    • No, I don’t think it’s like a vortex generator. I think vortex generators are more for directing airflow to a rear spoiler.
      It works more like a kammback. See:
      The angle of the rear of a beetle is not good for aerodynamics. A long sloping rear or a cut-off rear (like a kammback) is better.
      But this spoiler acts like the rear is cut-off just behind the spoiler.

  2. I too am wanting a spoiler. I am redoing a 72 sb. Were you successful in producing more spoilers?

  3. Hello Gerrelt,
    sent you a request for your roof spoiler. Hopefully you will still produce them. Looking forward to you reply


  4. Hi Gerrelt , can you give the price about your roof spoiler please ? possible to get it in full carbon fabric ?

  5. Hi! Interested in buying a spoiler for my 1303s 1973. Would appreciate information about price and shipping etc. greetings from sweden, thanks in advance.

  6. Hi Gerrelt
    I am all so Interested in buying a spoiler for my 1303s 1973. Would appreciate information about price and shipping etc. greetings from Denmark, thanks in advance.
    Kent 🙂

  7. I would like to order one of your rear spoilers. What is the price with shipping to the United States (Georgia)?

  8. Hi Gerrelt

    I like to order one of these spoiler for my Dad 1970 VW Bug. the rear window has a defroster in it! How much and can I get one real quick? flying to California on the 18th of November

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