how come you can run bigger tires with the stock wheels

 

Because the width and backspacing of the OEM wheels allow you to whereas the combo of the 2 on aftermarket wheels usually run a bit bigger.

 

i still dont see why that would matter

 

It's all about the wheel's width and backspacing. THey are as important to fitment as tire size. For and extreme example think about this. Look at the front tire on your truck. Now imagine that the entire tire was pushed outward 4 inches. Do you think there would be any rubbing? Most aftermarket offroad style wheels are wider and have less backspacing. Combine this with a larger tire and something is gonna rub unless you lift the truck.

 

i understand why a wider tire would rub but i dont see how this has anything to do with the rim.

 

The distance between the hub and the outside of the rim (backspacing) on stock wheels is different than aftermarket wheels which can cause rubbing. You can get aftermarket wheels that have the same backspacing as stock but if you go wider then they stick out the side of the wheelwells and will make your truck look like a Chevy.

 

less backspacing and wider rim......it is wider and sticks out more.

 

Just like Wandell said the wheel size is just as important as the tire size, I had to find out the hard way by not doing my "HOMEWORK"!!

 

if you have a 30x10 tire on a 8inch wide wheel with 5inches of BS will it rub just because you put it of a 10inch wide wheel with 4inches of BS