Laust Pedersen

Waterguy, very good explanation, but if I have read your post correctly, it seems a little fishy that the rear pressure would drop from 479 psi to 380 psi when the front (main) pressure goes from 479 to 480 psi (on a 5/33 valve).

I made a quick graph that I think shows what you meant in the text and also corresponds to my recollection of similar graphs I have seen. Maybe you should have said that the pressure reduction (of 50% for a 5/33 valve) applies to the incremental amount above the (33 bar) threshold.

My understanding of the justification for a reduction valve is that it in (almost) all situations) should prevent the rear wheels from locking up before the front wheels. If for example you drive on snow or ice, the 50/50 weight distribution would require equal brake torque front and rear just before skidding, no weight transfer. On a high friction surface (approaching 1g braking) the rear wheels need to have the brake torque reduced corresponding to the weight transfer, which is a vehicle characteristic. In theory if the car is lowered, the proportioning valve should also be changed slightly.

Laust

PS I am far from an expert on this, but merely applying some common sense and basic physics.