[For Brit Car list members, this is part of an ongoing exchange between John
Forrester
and myself.]
John,
>
> Tim,
>
> Sounds like quite a project!
It will definitely take me quite some time. There are many in-line things I
will have to do in addition to the work on the car itself, like learning to
TIG-weld, fixing up the shop in the basement, and so on.
I have seen the central tunnel of a late, tube-framed TVR, and it is indeed
pretty
wide. This is the most difficult part about using this kind of frame on the
Spit.
I thought about the fabricated sheet frame, Elan style, but really wanted tube
structures front and rear. It also seemed awkward to have both the
frame and body be sheet metal structures, and fit so closely together. Finally,
I don't have the equipment to fabricate a big, 14 ga. sheet metal structure,
whereas
I can cut and weld tubing a piece at a time easily enough.
Looking at the Spit frame, the outermost faces of the square box frame rails are
a decent distance apart at the bottom. A tube frame with that section width
would
be pretty stiff. Unfortunately, the body shell overlaps the tops of the frame
boxes
a bit before breaking upward into the tunnel shape. The seats overlap the
frame boxes
slightly as well. The two top frame tubes will not be able to be very far apart
as a result. However, I plan on crowding the seats a bit when I enlarge the
hump
area, which will help out. This central tube structure WILL be pretty tall,
though,
so I will get good stiffness in bending. I might be able to move the seats a
half-inch
to an inch outward, as well.
It's funny: I saw a Fiero at an auto show,
into which a guy had put some pretty nifty looking aftermarket seats. I never
wrote down where he told me he got them. Later, when I was trying to figure
out what
to do about my rotten seats, I could not find anything narrow enough and
visually
acceptable, so I had the originals rebuilt and upholstered in leather. Got 'em
now for the long haul, and must make them work.
I also am going to have small clearances between body shell and central tubes.
There's nothing there now to reduce noise except the carpet on the shell, and
I'm after
a very "elemental" sports car anyway.
Thanks for your suggestion about the "semi-inboard" brakes. I guess this
reduces
effective unsprung weight depending on the virtual swing-arm length that
prevails
at the rear suspension. I have indeed pondered the difficulties associated with
inboard brakes. In the Spitfire, they'd be right under the gas tank!
Maybe I'll spring for extremely light wheels, like real minilites, to recoup the
weight gain of a conventional rear configuration.
> Designing and building a chassis is an ambitious project but
> should be great fun. Just doing the modifications to the TVR has been fun and
> self satisfying.
I've wanted to do something like this ever since I read Colin Campbell's _Design
of Racing Sports Cars_ and the chassis design book by Costin and Phipps, when I
was in high school. When I'm done, you won't be able to get me out of that car.
> I envy your Atlanta weather, it is zero here today, after two day so constant
> snow. I was at Road Atlanta two years for the spring vintage races (I help
> fabricate and crew for a close friend with a TR-4) and it was neat driving
> south into good weather in late March.
Well, it's wet here now. Beats glare ice, though. I try to make it up to
Road Atlanta for the Walter Mitty Classic. There's an event called British Car
Day at Chateau Elan, a local winery, which happens to be across the street from
Road Atlanta. For a few bucks, one can lap there during British Car Day.
>
> Best Regards,
> John
Likewise,
Tim
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