Shake while braking is pretty much 100% warped rotor(s)
Large tires = larger weight = more shake.
Put wheels straight, remove front tire.
Rotate rotor while watching caliper, you can usually see the warp.
At speed it causes the caliper to vibrate, i.e. shake at 45MPH
Warped rotor can come from overused braking, pulling trailer alot or using brakes alot on long downhill grade, metal gets hot and warps.
Or a dragging(bad) caliper can cause rotor to overheat and warp.
So if you have to replace a rotor.....caliper should be replaced as well.
If there is a shake and it stops when braking then wheel bearing or tie rod end