OPM

I’ve been saying exactly what Fifth said, except he is concise. See the chart below. According to this imaginary graph 100% of the available traction for the plotted tire occurs at 45 PSI. Thus, for that tire, setup on that vehicle optimum inflation is 45 PSI. Anything over or under 45 would yield less than 100%. Nobody here is arguing that under inflating reduces grip. Of course it does. The point I was making all along is that over inflating is better, safer and more predictable way to achieve less grip. If you choose to under inflate to achieve the same results, it’s your business.

dsC32

The problem is that, assuming your chart for the tire setup in question is max traction at 45 psi on each tire, you still have understeer in your C55/32. You want to keep max traction at the front wheels for turn in capability. Therefor you reduce rear pressure to reduce understeer.