Can I only use a 305/70/16 for a spare if that is what I am running or can I get something like a 285 and still be ok?

 

Especially with 4x4 you should run the same size tire, especially if its for more than a few miles. Plus having all five tires the same looks better

 

If it isn’t the same size I wouldn’t use it. It will end up costing you $$$.

 

You will drive your computer bonkers if you throw a different size tire on there. I'm no expert by any means, but it's my understanding that there are wheel sensors on each wheel. They verify that the wheels and some type of motion/G sensors all show the vehicle operating without skidding, slipping or sliding. One wheel rotating at a different rate will throw all of that off. At the very least, you will likely get an ESP light, consequent loss of gas pedal, and computer-controlled braking on one side of the Jeep as you're trying to accelerate. Bottom line: You really need a spare the same size as you're other four tires.

 

Word

 

If you had to, you could manually disable the ESP. The spare tire would have to be on an axle that is open (if you have a rear limited slip), and you cannot use 4x4...