I am pondering one of those many potentially grey areas in my motorsport regs.
I am fitting bubble arches to my Mk1 Escort along with 15" wheels (slight overall diameter increase). Although responses to a previous thread (which I now cannot find!) of mine suggested that 15" wheels should fit inside the standard tubs without much drama (tarmac rally car so not running low like a track car) I am still thinking of tubbing if the regs permit.
My regs read;7.4 The addition of front and rear aerodynamic aids, side skirts and mudguard/wheel arch flares is permitted, provided these are identical with the components originally fitted to a production model of the same body shape and the items are fitted in accordance with the total original package configuration.
Where an automobile does not have access to such components, wheel arch flares may be added by integrating the flare with the guard or bodywork or by bolt-on means, provided that the increase in the total width of the bodywork is less than 100mm and that the flare may not exceed the radius of the original wheel arch opening by more than 200mm. (Refer to diagram 7.) In this case, the maximum track increase allowed is 100mm and for the purpose of wheel and tyre clearance, it is permitted to remove up to 75mm of original bodywork measured radially from the edge of the wheel arch outwards. Any cavity exposed in a door or wheel arch through the removal of metal must be covered by the addition of a metal closing panel. Any body joint protrusions must be rendered safe. The operation of any door must not be affected.
The bubble arches were never fitted on the production line but were available via the RS parts system. First question becomes do you think bubble arches meet the criteria in red above i.e. a component originally fitted to a production model? I think yes.
If so, second question becomes how did Ford suggest these RS bubble arches were fitted? Did they ever suggest that the standard tubs be enlarged in the radius? I would assume not as they only seemed to use 13" wheels back then (although I believe that Ford did try 15" at one time so did they extend the tubs then??).
Gary has previously posted up the following showing the 2 methods of fitting a bubble (hope you do not mind me reproducing Gary). Did Ford specify one or the other i.e. take the tub out to the wing or take the tub out to the new bubble? I was thinking of using the middle one - seems easier and easier to repair the arch if it gets a knock.
I ask the above as although there is no doubt at all that I can fit bubbles within the regs I am hoping that there is some historical precedent for increasing the tub radius.
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