find it necessary in order to match if you do a front rotor just to keep it all semetrical. Went to a GMS slotted and dimpled rotor, hawk HPS pads and stainless lines to hold me over until the time was right for funds to be spent on a big brake kit..
I don't think it's a good idea to upgrade the rear brakes while leaving the front stock. There is a reason most cars are built with front rotors being larger then the rear and that is to keep the braking bias toward the front which produces safe understeer while braking.
The new mustang has 12 inch rotors up front stock if you put 13 in rotors in the back that shifts your bias toward the rear which causes dangerous oversteer during braking especially in turns or wet weather situations. Same reason why when you do a pad change in the rear you better match the front compound or better replace all 4 brakes at the same time to keep your bias the way it was intended to be toward the front.
I'd be careful and do some more reasearch before trying this out.
Walter,
It is a foregone conclusion that a front brake upgrade precedes one to the rear. My question was rather to determine if anyone found it even necessary to mess with the rear OEM system at all. i.e. is it adequate for all high perfomance applications? Most of the people I talked to say to go huge with the front brakes but no need to touch the rear.
Point of fact, I really hoping to find someone who had made that upgrade to the rear to get their perspective.
A good aftermarket manufacturer, like stop-tech, does a lot of research and testing to get the bias of their BBK just right. So going with a larger rear disk could have an adverse effect, though the one to call to ask this question would be the manufacturer of your BBK.
All that said, the ABS will adjust the bias of the braking system when the brakes start to lock up, and there is little to be done about that.
Dan