What you're experiencing is neither "better braking", nor "better control", it's "better traction" which translates into "better braking" by allowing more brake force without loosing traction.
are you done? because you're no closer to reality now than you were when we started this.
I understand that tires don't act according to the "perfect" coulomb friction theory. But the the fricitional force available is still a function of the normal force on the tire. It is just that instead of:
F(f) = N*cf it is something like F(f) = (N**x)*cf
where:
F(f) = maximum frictional force available N = Normal force on the tire cf = coefficient of friction x = a factor somewhere in the range of 0.7 to 0.9
But this does not affect the main point - if part of your load is on a trailer without brakes, then you have less normal force on the vehicle's tires, and therefore less maximum braking force available. If you have less maximum braking force available, you can't slow the load as quickly. I know it is a lot more complicated when you start accounting for weight transfer, and other factors but I am certain that if you have two otherwise identical vehicles, one with all the load in the bed and one with the same load on a trailer that does not have trailer brakes, the one with the load in the bed can stop shorter.
Ed
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