Frame question

Ant · #1 (**permalink**) 11-04-2003, 12:25 AM

Hi Bob,

I have a very similar to look at chassis design as the ERA, and wide 4X3X125 Tubing at 26.5 spacing!
I have another maybe silly question, have you ever thought or done for a customer for racing, adding a small tube backbone with the confines of a standard or slightly larger transmission tunnel, and have going out to the front suspension, much like the Cobra Coupe, which claimed up to 50% more stiffness, and this would keep the car inside the classic car design criteria of the sixties!

Having said all that there may a problem with this idea, on the wide chassis rails part of the structure would be welded in from the main rails on the "X" section center bracing piece due to the tunnel intersecting on its taper to the rear of car, but from what I have read if you put one ladder above another ladder it should improve stiffness noticeably, even if not the ideal concept!

There is another idea as well, give up on modifying what I have got and start again, and then all I might have is a modsport that the authorities may not let race at classic events, as the vehicle is not within the guidelines.

strictlypersonl · #2 (**permalink**) 11-04-2003, 04:16 PM

If the tunnel is completely enclosed, or the open area is very well braced, it can add quite a bit of torsional and beam stiffness. However, the problem with adding a backbone to a wide chassis is integrating it into the whole structure. It must be connected at the front and rear to something that will transfer loads from the front and rear suspension, or at least the main chassis rails close to them. It can be done, but you may have to add more than just the tunnel.

The "nice" thing about the original 289 chassis was it was so narrow that it was practically a cakewalk to put a central spine on when they did the Daytona coupe. Of course, the 289 chassis really, really needed the extra stiffness.

One of the most radical of the backbone chassis designs - the Lotus Elan:

Ant · #3 (**permalink**) 11-04-2003, 06:45 PM

Strictlyperson,

Thanks for your thoughts, the Lotus is a nice little setup they perform real well even by todays standards!

Been giving it a big think, and if I move the main chassis rails inwards from firewall/baulkhead rearward, widen the glass transmission tunnel an inch of two mainly in the back half of it, then I can fabricate a tube frame much like the Cobra Coupe, this will be no problem tying in to the rear suspension pickup, but it will require carefull location of tube to almost the front cross member, once I know where things are going.

I realize moving the main rails in will reduce stiffness etc but the backbone frame should hopefully make it markedly better!

Looking on the forum cars like Richard Hudgins JBL would be great for the track, and they look extremely well engineered, but officials would shudder here unless you ran the car in a real modified class, which it is compared to my jigger!

grumpy · #4 (**permalink**) 11-17-2003, 08:04 AM

StrictPerson,

The trick at LOTUS, and CHAPMAN knew this, was to keep the patch of the four tires on the tarmac, GEOMETRY, not frame rigidity.
Well noted follow up. For the times Chapman, Costin, Broadley, and a mere handful in the UK understood that. The patches were small and the new euro "radials" had just hit, it was tough blending that technology of street then crossing over into racing with that type of tire. Good days for the "small shop bunch".

grumpy