Drag Racing Tech - How to tell if I need adjustable lower control arms

What or where do I measure? I have the umi no adjustable tubular ones with poly ends. But what measurements do I take to check.

The only time I have witnessed "needing" them is when you run a 28" tall tire (bias ply slick) and you need to center the rear so the edge of the tires is not to close to either side of the wheel well.

Looking at the sideview of a rear wheel on most cars you may see the tire closer to one side or the other.

I am sure there is other uses but that seems to be the big one everyone runs into eventually.

I did the Neanderthal trick and clearanced for my 28s at the track :judge:
I just didn't know if there was a certain point to measure to double check. This year I'm trying out a 26" tire to see if I can use the 4:10s to my advantage I hope

I think the real need for them arises when the thrust angle of the car is off. Meaning that the rearend is no longer centered in the car and one side is either further forward or rearward than the other. It's very hard to see this with your eye and simply lining the wheelwell up in the center isn't an accurate measurement. You can measure from the center of the front ball joint to the rear of the lower control arm on both sides in order to get a rough measurement. Otherwise, an alignment machine will tell you instantly how the rearend is sitting in the car. Both arms can be the same length but after years of hard launches the lower control arm mounting points will be slightly different.