I made a statement two posts ago about revamping the frame design adding 30 pounds to the car. That was an error based on the fact that I added or relocated 8 frame braces during the redesign so I figured the weight for all 8 changes. Then last post I stated the empty car weight was 1450 pounds which was accurate based on calculating the length of every frame member and multiplying that by the weight per foot of tubing for that size tube.
There are 2 different tubes used in the Sprint-T. Most of the frame is made from 1.5″ X 0.060″ wall round DOM tubing, except the rollover structure which is 1.5″ X 0.120″ for rules compliance. Now because of the design there is room for interpretation as to where the frame ends and the rollover structure begins, but I’m taking the interpretation that any diagonal braces that touch the rear hoop inclusive are rollover, and everything else is frame. There are a lot of tubes in the frame, the front and rear hoops are the longest at roughly 16 feet apiece as they wrap around the body, and then the upper and lower frame rails at roughly 100″ each for a total of 400″ or just under 34 feet total. Then there are the front suspension mount, the internal diagonals for the rear hoop, the bracing inside the top halo, and the rest of the diagonals that connect everything together to make one solid structure. That comes to another 40 or so feet in mixed sizes.
So, all told the Sprint-T frame carries a few more pounds than the Speedway kit frame, but is orders of magnitude more stiff, both in bending and especially in torsion. The Speedway frame is 2 hunks of 1.5″ X 3″ X 0.120″ wall rectangular tubing with round tube crossmembers to hang the engine and transmission from. Adequate in bending loads under all circumstances, but lacking in torsion to be charitable. It is an upgrade from the Model T frame or any OE Ford frame used back in the day, but that is damning with faint praise. It was designed as a cruising or freeway frame, not for racing and especially not for racing around cones set up in a parking lot. It was not made for installing a rear roll hoop that meets SCCA safety rules for one thing and as an open car (no roof structure) it would be required to have a full cage, and there is no place to mount the front hoop either. Now there is a place to mount a drag race style cage, but not an autocross legal cage. This is annoying because using the kit frame would make the build so much easier. And probably cheaper, too. There would be work involved with relocating the suspension pickups to prevent the tire-lifting behavior of the stock rear axle and the resulting power oversteer in tight corners even with radical bigs-‘n’-littles tire sizes (I saw a YouTube video of a bucket getting sideways off a corner with 14″ wide rear tires and 3″ wide fronts).
Witch on a Bicycle 