Brake pumping/throbbing

Since I put my larger tires on my truck (from 265/75/16 to 285/75/16) and my spacers when I step on the brake fast, or hard I get a tiny bit of throb, like the brakes are pulsing. I don't think its rotor warp, but I guess it could be, are my new tires just really heavy for the brake system. I haven't got a brake proportioning valve kit yet, is this what it is? thanks ahead of time

 

anyone?

 

just saw this.

well....the added weight could be causing alotta drag on the rotors....which in turn, the heating and cooling of the rotors could cause them to warp. may be time to go with a beefier set of rotors.....or a set thats slotted that can cool down better.

 

Is it nose-diving a lot when braking?

 

no, it doesn't feel like its nose diving