Beetle floorpan stiffening help.

[Pete Rodder]

Here's one to get you thinking.
I am building a hot rod beetle out of a badly home made convertible and am concerned about the floorpan flexing as the body doesn't have a roof. A lot of buggy builders put 25x25mm box tube around the perimeter but I can't imagine that makes a lot of difference. VW cabrios have special stiffeners underneath but they are £185 per side! - which is half my total budget. A US company called Eyeball Engineering makes stiffening beams(30x50 box), which fit into the body mounting bolt channels, which could be replicated using 30x60 box ( I think this is a standard size) but require a fair amount of work to shape. A roll cage would be even more difficult /expensive
Have any of you fabricators got any easier, low cost ideas?

 

[dubber91]

how pretty do you want it? beetle floorpans flex because they arent triangulated up to the body - You know how they herringbone the chassis when they shorten them for buggys? similar principles...

 

[Pete Rodder]

I would rather have practical than pretty. The floorpan hasn't been shortened but the but the sides flex (with the body off) and I won't have a roof to stiffen the body and am not sure the heater channels will provide enough support. Any suggestions?

 

[MrFluffy]

how about using the cage to brace the chassis in the vertical plane? Front tie right into the framehead somehow, and at the rear hoop onto the back of the pan, and put some struts to tie onto the rear frame horns or something. You can have practical, pretty and solid that way and good roll protection to boot.
Awkward fab but worth it for the results I reckon. You'll find assistance from a few people here if you did go for it.

Im doing the same on my esprit chassis'd kitcar , as the original esprit X form chassis was notorious for flexing, but adding a cage tied into the X legs gives it a huge increase in rigidity. It had a bug chassis at one point in its life too, and that sagged as soon as we lifted the body off (nova)...

 

[dubber91]

It wont be cheap to do properly - You really need a cage to add strength in the Z direction.

 

[hotrodder]

As said there isn't really a cheap and easy solution. Many of the 356 speedster replicas have a subframe bonded into the shell to stiffen things up. Granted they're on shortened floorpan too but not too much scuttle shake in a Chesil speedster. Not exactly easy and cheap but less work than a full cage.

An idea of the layout here, note the A and B post triangulation. Not really visible in the pics but there's a substancial front crossmember/bulkhead reinforcement as well as the clearly shown additional rear crossmember. Speedsters are wider than a beetle meaning it all gets hidden behind wider sills and inside quater panels. Could maybe fit 'em inside the car just inboard/ on top of the existing heater channels and tie into additional crossmembers at the bulkheads. Triangulating to the A and B posts would be tricky to hide as there's very little space between the outer skin and interior trim