I have a 98 ram 1500 4x4 , currently i have a LT315/75R16 tires on, but its it possible to change it to LT285/70R16? The change is the 2 numbers which is the width

 

LT - Light Truck.

285 - section width. (widest portion of tire mounted on specified rim.)

70 - aspect ratio. Ratio of width, to sidewall height.

R - Radial tire.

16 - rim diameter.

You can certainly go with those tires, they will be a couple inches shorter, and a bit wider.

 

Use this fancy little tool:

http://www.1010tires.com/Tools/Tire-Size-Calculator

 

^ less wide.

your current tires are 35 inches tall
285/70/16 are just under 32 inches tall and 1 inch narrower

http://www.1010tires.com/Tools/Tire-...5R16/285-70R16

 

I always thought this number was the average of the section width and the tread width.

 

What bout LT275/70R16 using my stock rims?

 

Basically a 31" tire. 4 inches smaller than what you have now.