For what it's worth, the torsional stiffness of a 1.5mm steel chassis plate versus a 1.5mm aluminum plate, the steel part would be 2.8 times stiffer (assumes same geometry of the plates). But lower that steel plate down to 1mm and since it's a function of thickness cubed, the 1mm steel chassis plate is now 20% LESS stiff than the 1.5mm aluminum plate (assumes same geometry other than thickness). Personally, I would make the steel plate as thick as I could and not go over the min weight requirement. I think COG is more important than chassis stiffness.

It's an idea he took from his nitro car. The lower front arms of his nitro attached directly to the bulkheads which let's him make the front of the chassis just widen enough to accommodate for the bulkheads.

yup. CG is way more important as that determines the arm angles needed for the correct amount of roll. Braces can also be added or remove for the correct stiffness

To me, the reason COG is the most important, it's the COG and the track width that determines how much weight is transferred to the outside tires in a corner. And since the track width is controlled by the rules, all that is left is lowering the center of gravity. And the less weight you can transfer to the outside tire, will increase overall traction. Since you don't gain as much traction on the outside tire (due to higher load) as you lose on the inside tire (due to loss of load), then the most traction you can have is zero weight transfer. This is only possible if your center of gravity was on the ground and of course that's impossible, all you can do is make the COG as low as you possibly can. And remember, it doesn't matter if you let the car roll more, it will still transfer just as much weight to the outside in a corner as a car with little roll. But if you soften one end or stiffen the other, then the stiffer end will take more of the overall weight transfer. And that's how you tune a car for mechanical grip, soften or stiffen the ends compared to one another. Sorry about boring everyone to death!

Steel is also way denser than aluminium. Even at 1mm thickness it's going to be twice as heavy as a 1.5mm aluminium plate.

1.5mm plate maybe around 60 grams.

1mm plate even if lighter (e.g. 40 grams) will lower the entire car weight (e.g. battery, motor, bulkheads, etc) by 0.5mm.

Even if they have 1mm at the worlds I doubt it would make it to production. Like I said, at 1mm you get knife-edging in the countersinks. Good luck if they do produce this chassis and you get into a major crash.

This is why it's good to use steel. As long as you don't go over the min weight, you can take off the added weight and replace it with a steel chassis which puts all the weight as low as you possibly can.

Yes and no, the issue with steel is that the strength to weight ratio vs aluminium is lower, so to get enough strength you might end up over the min weight.

For standard SAE sizes (4-40, 6-32, 8-32, etc) the standard head angle is 82*. Undercut (low profile) have a head angle of 100* (such as the ones on the original gold tub RC10).

Metric screws have a standard head angle of 90* (standard head height on 3mm countersunk screw is 1.7mm). Undercut metric screws have a head angle of 100* (3mm undercut countersunk machine screws have a 1.3mm head height).

Not sure if Xray had something custom made with a greater head angle.

Yea It they might be a custom order. I know there's 110 counter sink cutters and I would assume there's companies that make them if you request them but they probably don't do full production runs as the demand is most likely very low.

Isn't there a greater risk of permanent bending/tweaking with steel, especially when compared to carbon?

aluminum is less likely to hold it's than steel. This theory can be tested by bending a piece of both materials. you will see that steel can be bent more still return to it's origin while AL with minimal deflection will be permanently deformed. The problem with the steel chassis, is that even though the plate may have the same torsion properties, the chassis will see higher stress due to lack of material providing the necessary rigidity in the vertical axis to prevent damaging the steel plate. I wouldn't think about this too much when even the pros are all saying it's not an easy option to drive. If the top drivers are struggling with it, imagine the carnage us normis will cause with one of those plates lol

I personally have never ran an AL chassis on my electric car but in the nitro world, replacing a chassis because you hit something isn't a rare occurrence.

which Aluminum?
which Steel?

Orlowski's chassis got bent at the worlds. The only decent one I have seen looks to be the AMX one. The AMX chassis is a very different shape due to not using a conventional shock absorber though. I heard that some of the steel chassis that used were only 1mm thick