Creating a roof spoiler

Then I started to shape the spoiler using some plastic strips and some wood.

Shaping the spoiler


Shaping the spoiler sideview

You could consider this as a mold, the area between the edge of the roof and the plastic/wood construction will be filled with glass fiber reinforced polyester resin.

Of course I don’t want any polyester resin directly on my beetle, so I taped it all up. I used some play-doh from my kids to shape the corners.. Smile

Shaping the spoiler painters tape


Because this (painters) tape isn’t enough to protect the car from the polyester resin, I put a second layer of aluminum tape on it:

Aluminum tape


And because the aluminum tape is to slippery, I put another layer of painters tape on it:

Second layer of painters tape


And, after that, I put some plastic over the beetle, to elimnate the risk of accidentally dropping some polyester resin on the car!

Wrapped in plastic foil


I cut the plastic open on the part where the polyester resin goes, just like they do on an operation.
Then I bought some glass fiber reinforced polyester resin:

Glass fiber reinforced polyester resin


But it turned out I had to buy another can! Eventually I put 1,5 kilogram polyester resin in it:

Roofspoiler shape filled


When it hardened I sanded it down, and put some filler on it:



And I had to repeat that multiple times…sanding, filling, waiting for it to harden, sanding etc.. Frown
The result:



And all the tape and plastic remove, held on by my lovely assistant:

Testfit unfinished spoiler


Now the edges and the underside had to be smoothed.

After making it all a bit smoother and nicer, I discovered the spoiler didn’t really fit nice to the rear window. Apparently the polyester warped a bit while hardening, probably because it’s a big mass of polyester. This is not going to work..


  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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