For the exact same reason as on a front/rear split system. To prevent too much pressure from going to the rear brakes during hard braking (when the weight is shifted to the front wheels) to avoid rear wheel lockup.
you have two brake cylinders so the car will still work if one fails. Each system drives diagonally opposite wheels because it will still be safe to drive with only one system working. (Think of if you locked up the front wheels… massive understeer. lock up the rear and you spin. but lock up diagonal sets one at a time and your car will still be controllable) the proportioning valve gives you extra pressure up front. under hard braking, up to 70 percent of the grip is on the front wheels, so the front brakes usually have larger disks/calipers or drums and also have some bias so they get more line pressure
on a side note, my ford is much simpler (at the expense of having no abs and a lot of brake fade) I have disks up front and drums in the back. When I stomp on the brakes, the front disks are more powerful than the rear drums, giving a kind of brake bias without needing a proportioning valve. My car also has a ‘diagonal’ layout like the one above, just no proportioning valve.
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For the exact same reason as on a front/rear split system.
To prevent too much pressure from going to the rear brakes during hard braking (when the weight is shifted to the front wheels) to avoid rear wheel lockup.
you have two brake cylinders so the car will still work if one fails. Each system drives diagonally opposite wheels because it will still be safe to drive with only one system working. (Think of if you locked up the front wheels… massive understeer. lock up the rear and you spin. but lock up diagonal sets one at a time and your car will still be controllable) the proportioning valve gives you extra pressure up front. under hard braking, up to 70 percent of the grip is on the front wheels, so the front brakes usually have larger disks/calipers or drums and also have some bias so they get more line pressure
on a side note, my ford is much simpler (at the expense of having no abs and a lot of brake fade) I have disks up front and drums in the back. When I stomp on the brakes, the front disks are more powerful than the rear drums, giving a kind of brake bias without needing a proportioning valve. My car also has a ‘diagonal’ layout like the one above, just no proportioning valve.