Aluminum Tub Work & Re-Work


Much progress since the last post on the site here, though there have been a few brief images posted to Instagram. A lot of work, re-work, and further re-work happening here. Have done a lot of re-jigging to get the loads and material in the right places, not a lot of work done yet to bring the weight down yet, but that’s still to come.


You can see here the front still needs a few things to complete. There is the basics of the front sub-frame, which is detachable (as is the rear), but still needs the lightweight framing for the radiators and coolers, not to mention the fiberglass and/or carbonfibre splitter.

The steering rack is a slightly modified Porsche 930/914 manual rack, which will provide amazing steering feel, and with the tuned geometry, a nice weight to the steering without being too heavy or cumbersome.


The rear detachable sub-frame is closer to completion with all of the suspension hard point defined, and ample clearance for all the big ticket items. A G50 type transaxle is shown here.


You can see the Corvette C5/C6 suspension uprights are used both front and rear. They have fantastic dimensions and weight right out of the box (or castings), can be used for driven or non-driven wheels, and they are relatively plentiful and affordable.


The roll cage fits nicely within the body work, no complex bends, and all a 7″ radius which should make them easy to bend accurately. The roll cage for the street version utilizes 1.625″ DOM steel tubing with an 0.90 wall thickness.


The inboard suspension went through many revisions, here you see should be close to the final revision. I see a nearly linear shock travel to wheel travel ratio of 2:1, giving ample compression and rebound travel. One thing you want to make sure is you don’t run out of droop travel, as a wheel off the ground provides zero traction, and can make for some very scary and unpredictable handling characteristics.


Side view of the tub; you can see the lower sill height for easy ingress. This is especially important for the central seating position as it’s difficult to get in automatically.


In designing the front and rear suspensions together, I was able to re-use the design for the bellcranks for front and rear, and left and right, which saves time, but also will result in lower cost to produce as there is one design. I can also spend more time optimizing it for stiffness and strength which I’ve yet to do.

The coilover dampers chosen are all aluminum QA1 units which are double adjustable and will be valved for this specific application. Other options obviously available, but these are a fantastic bargain for what they offer.


The roll cage, in basic 1.625″ DOM steel tubing, weights just 13kg, but provides more torsional rigidity than 1.5″ 0.120 wall DOM tubing.


The aluminum parts of the main tub, front and rear sub-frames. All off the shelf square and rectangular aluminum tubing, almost all 0.125″ wall thickness as well, making welding much easier as wall thicknesses don’t vary, requiring different welding techniques. The entire tub and sub-frame assembly currently weighs in at 126kg, which is right on target, however there are still some work to be done, both in adding more material, but also removing some from areas to keep it on weight target.


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