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MG Midget and Sprite Technical - Chassis Stiffness 1275 vs 1500

Is there any benefit in using a 1500 chassis as the basis for a replica where the body work is replaced by GRP, for example a Sebring Sprite?

I'm thinking in terms of the chassis stiffness with the bracing added for the rubber bumper models over earlier models.

Or can an early chassis be stiffened to compensate for the loss of steel panels beyond that of a 1500?

If so how & where should the reinforcing be applied?

What do racers do to strengthen their shells?

Any feedback / ideas would be appreciated.

Thanks
P R Clark

Both chassis are structurally sound before the outer panels are fitted
I personally don't like the extra strengthening for the fact that if you do have a knock the force is transferred to the bulkhead or towards the axle tunnel causing further damage.
I have a Sebring and whichever chassis you use apart from a Frogeye you will need to change things like inner rear arches B posts B post strengtheners front scuttle panel and doors to name but a few. Lenham do a kit for later type cars meaning you can keep the doors.

Hope this helps
Dave Pratt

"What do racers do to strengthen their shells?"
fit a full roll cage... and then lighten evrything else as far as possible / rules allow :-)
David Smith

Thank you for the contributions so far.

I agree adding a roll cage will help strengthen the shell but most, if not all the designs I've seen do not extend beyond the cockpit. At the front I was thinking about the suspension attachment points and where the H frame attaches to the inner wings, footwells & floor.

Then at the rear, I imagine that removing the panels that surround the boot lid must introduce some flex as I'd assume the GRP is less rigid without all the bracing the steel panels have.

P R Clark

Paul as Dave P said, the shells are structurally sound *before* all the outer panels are attached. Ergo a g/f rear end makes no noticeable difference.
I haven't studied 1500 shells in minute detail but I'm not aware of anything at the front which will improve the stiffness over the earlier shells; but am aware that the upward 'kick' in the chassis legs is greater on the r/b shells which alters the caster angle - not sure whether this is a good thing or not?
David Smith

The shell in its original form as the frogeye was designed to work without the enclosing panels on the rear end. The main tub has two box sections running down each side (the sills) and the centre transmission tunnel. Originally all the suspension stresses were fed into the floor pan. The later spridget with semi elliptic spring move some of the stress to the rear but with such a light car its not a problem.

At the front the pick up points/ inner wings/footwell and floor make for a rigid structure. The addition of a roll cage gives added rigidity.
Bob Beaumont

This thread was discussed between 26/01/2016 and 27/01/2016

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