I completly agree with you. To me the photos show a car with not enough roll stiffness (Total) for the lateral grip those tyres can generate.
There are a number of ways to increase the roll stiffness. Each has a pro and Con. If it was me (and it was last year) i would do exactly as you are, add a rear bar and then test.
Once you get the body roll under control, then see what is next to balance to roll stiffness distribution.

Regarding your point about RC (Assuming front RC) I would think it has the opposite effect on body roll and wheel lift (with all other elements being equal) i.e higher front RC will decrease the required roll stiffness and body roll (increase geometric weight transfer at the expense of elastic). If the RC was at CoG height, body roll would be zero.

Please keep us posted with the results. I am keenly intersted.

Bryan

ah, true... RC at CoG = no roll. At least in theory... I made no point about RC and roll stiffness though. You sound like you assume that lowering the front RC will increase body roll and lift the inside higher?

I probably also wasn't clear about what RC we're actually talking about - lol. It's all clear in my head! That part of the track where it's two wheeling excessively is Lover's Leap. It's at the end of a long left hander, so the car is already fully leaning over before launching off that creast. We're dealing with where the RC migrates to with all the body roll at that point, not the static RC. Increasing the roll stiffness with a rear swaybar will reduce that dynamic RC change. And dynamically, with body roll, it would be getting higher. That's why imo it's lifting the car so much at that point - the RC is too high - at that moment. Textbooks generally don't cover what happens if you throw a fully loaded up car off a cliff at the end of a corner! lol
But lowering a RC will generally result in less chassis lift and more hunkered down cornering attitude and less of these kind of antics, despite compressing the outside suspension more.

Yeah I agree with you. I was going to discuss RC migration but was worried about bogging your thread down. Too late now sorry.
I modelled my 1200 front RC in CAD and can see it's migration with moving one/both struts, it does move around quite a lot (Can change RC height as well. There appears to be definite benefits to limiting the RC migration by limiting the overall suspension travel.

it's interesting to talk about, but difficult in text only... yep, struts are notorious for poor dynamic RC control. The more I talk about it here, the more I'm starting to believe a rear swaybar might actually solve most of this, so it's been a useful discussion from my perspective.

another angle of the big wheel lift out of the hairpin

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Not too bad here coming out of the 2nd loop. Seems to show things really only go pear shaped when it rolls a bit too far - either by going off that off camber drop off, or the deep road camber and being hard on the power out of that hairpin. Or maybe I just need to go on a diet! lol might whack a couple bags of cement on the passenger floor

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I'm liking this discussion too. +1 for rear bar. Maybe try swapping some front bar for spring too. Is your rear spring much higher rate than std?
My car used to fall over on the outside rear and then lift the front. It would then over steer. I added rear spring as well as rear bar. it seemed a little counter intuitive at the time. I don't think it lifts the front at all now.

unfortunately I only got one practice run in with a rear bar but it definitely helped keep the inside front planted (blew engine before the end of that run so hard to compare lap times but can see it in the datalog).
I have mentioned in other threads that I think cars like the 120y and 1200 work best if you limit the total body roll. Excessive leaf spring movement does nothing for the rear geometry (except trying to rip itself apart). Same goes for the front end and how wild the RC movement can be + jacking effect. Keep it flat and go-kart like. Bitch to drive but suspect the way to make it go fast.

Rear springs got an extra leaf after the first day at Lakeside when it was even so soft it kept hitting the bumpstops and jumping sideways. Rough measurements and calculations from me kneeling on the middle of the spring after that came out at about 220lb/in. Not sure if that stays consistent through the full motion of the spring though...

I need to have another go at those leaves too because it's just getting a slight bit of axle tramp doing burnouts before the run. It was fine on all the other tyres I've used, and at doesn't axle tramp at Lakeside when you get some wheelspin in 3rd. but the stickier A050s must give the springs a bit more wind-up. I'll add a half leaf to the top to counter that. That will probably lower it a little bit too.
I might get some gas shocks for the back while I'm at it. Because this build was done quick and on the cheap, it's still using the stock shocks that were in it when I bought it.

The front also got much stiffer springs after that first Lakeside day, up from 175lb/in to 300lb/in - actually a touch over that because I cut half a coil off. The 23mm Maddat sway bar is on the middle hole both sides.

I'll get it sorted sooner or later - that's the fun part for me anyway. Tinkering around trying to work out how to make them faster. This was only the first revision after trying a deliberately soft setup at first.

My poor math but big butt measurements felt 275/300 lb in front with a l series in the 1200 was perfect. Before I added the rear load spring I felt the rear wanted to lift over the front too. Flipping and adding the load spring with a home made rear sway bar I got off here definately improved it. No oversteer and quite balanced. When crumb added Tokico gas shocks was even better.

I'm following similar in stanza but I'm still trying sort rear end. The link coil setup is totally different for me.