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rolling radius it the radius of the tyre with weight on it. so from the centre of the hub to the ground. this is how it determines the height of the axle centre as a datum point.
i have built cars in the past that have the same annoying trait that you are trying to deal with now, the problem is that anti-squat numbers tend to increase exponentially as ride height increases due to torque. say your rig works out as having 200% anti-squat. when you get into it on a climb (the more traction the worse it will be) that figure can quickly rise to say 300 or 400% as the torque starts trying to drive the rear axle under the car. abviously it can't drive it under the car because the links stop it, so it lifts the rear of the car up instead. now, because the driveline torque is trying to lift the left rear as well, it will lift that side and transfer weight to the right, which will generally either stay at a static height, or compress, depending on how severe the action has become (your roll centre height plays a big part here too). the other thing that has been going on while this has been happening is that your left rear coilover isn't supporting any weight anymore, as the link has taken up that load, so it is stretching out under it's own steam as well. so you can see how quickly all these little things can add up to create a problem that grows upon itself within seconds.
now, if the car doesn't fall over and you continue putting on the torque eventually so much of the car's weight is transferred onto the links and out of the springs that the car loses traction for a split second, as the wheels slip the car will drop back to below ride height, then as it finds traction again, the cycle starts again, this is what causes most cars with linked suspensions to get the bounce up when climbing.
i would hazard a guess that this has started since your axle swap because whoever burned the rear axle together has increased the vertical seperation of the link mounts (this is good, and a logical thing to do) this has, however moved the instant centre (point where torque is applied to the chassis) back closer to the rear axle, and in turn pushing the anti-squat number up. it was probably quite high as it was, so it's a straw/camel's back kinda thing.
easy experiment: put a bodgy, temporary limiting strap on it (a ratchet strap around an upper link and a chassis crossmember or something) and try the same climbs and see what happens.
hope this helps.
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