Creating a roof spoiler

Roofspoiler beta2 finished

I decided to create my own roofspoiler. Roofspoilers are for sale (Remmele sells them), but these have to be glued to the roof, which I don’t really like, and creating my own is more fun.. Laughing

I had the idea to put the roofspoiler on the top of the rear window.
Now, this article actually consist of two stages. At first I wanted to create a roofspoiler out of glass fiber reinforced polyester resin, and then stick it to the rear window with double sided tape.
But that didn’t work out (is explained in this article), so that “spoiler” became a positive mold for the second spoiler. That one was made using glass fiber drenched with polyester resin.

OK, here we go.. Here’s a cardboard mockup of the “design”:

Roofspoiler carboard desing with degrees

Somebody told me that a wing or spoiler shouldn’t exceed 12 degrees, or else it will become an obstruction instead of a deflector.

Roofspoiler cardboard design

Although the goal is to reduce drag, the design must be aesthetically pleasing too!


  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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