[KiaTech]

Given enough time and money, anything is possible. Simply buy two new front rotors, weld up a caliper mount, and pray like hell it fits... or chop/cut/weld until it does. Lose the park brake, but who needs those, anyways?

The point here is the time and money. Do you have lots of either to invest on something that is considered completely cosmetic? Maybe you could go about it the other way; purchase the front rotors, spindles and calipers from a base/EX (possibly axles, bearings... a whole ton of stuff)... then the difference would only be 3/4" instead of an inch and a half. But your braking performance may be affected - there is a perfectly good reason a whole bunch of engineers gave the car bigger front brakes... I personally wouldn't mess with it.

 

[KiaTech]

Increasing the diameter of your brake rotor (be it on the front, rear, or both) may improve braking distances, but likely not on most recent vehicles. 99% of street driven cars have absolutely NO need of a brake improvement over stock, except possibly a change of pads. Generally bigger brakes mean more surface area, which can increase 'grab' and improved cooling to resist fade or squish, but with ABS now kicking in and doing most of the work that difference is subjective.

The rule is this: As long as you can lock up your brakes (or activate ABS), improving brakes will not serve any purpose to improve brake distance.

Things that really can improve braking? Better tires, first off. ABS will allow you to maximize your braking by not allowing lock up. But lock up is not the point where the brakes grab too hard, it's the point where the tire's friction with the road is overcome by the pad's friction on the rotor. So by increasing your available traction on the road, you'll increase the amount of force your ABS system will allow before it needs to step in. The next option to improve braking is a better brake pad. Higher 'bite', lower dusting, more fade resistance - all factors that can help but only in a 'track' or race type scenario. Most people's cars will simply never brake hard enough to require these kinds of changes.

As for changing things and messing up the ABS (and by association the ESC), not true. It simply looks at axle speed at all four corners, steering input, speed, etc and tried to guess the driver's intentions, and helps them get there. As long as you don't change diameter of one tire, or have your alignment seriously askew, the system will adapt and keep things going your way. As long as axle speed is relative to the inputs it has, it doesn't care what size brake rotor or how much money you spent on Yellowstuffs, it only knows that once it hits 0rpm on one wheel, it's going to reduce brake pressure to that wheel, until it sees rpm increase to spec, and then repeat.

Oh, and there ARE vehicles out there with larger rear brakes than the fronts; I refer anyone interested to the spec sheet for the 2011 Sorento. Rear rotors are exactly 1 tenth of an inch larger than the fronts.