I bought mine used with a 15/40 ratio. It was too tall to crawl real slow in 1st for me, since I also pull a small mower deck.

I put back the stock 13/40 ratio and it's been way better for the woods and it also allows me to use the gears a lot more. With the 15 up front I needed 1st gear to climb steep hills, now I can hit them in 2nd no problem.

 

The stock ratio on the rappy is 13/38 and that lets you pull up to a steep hill in second, come to a stop, and then power it up, i could probably get away with using 3rd gear from a slow roll. Im gonna drop the front 1 tooth just so i can utilize the higher gears, on trails i hardly ever have to go past 3rd.

 

ur sprocket number depends on the type of riding you do...
if you like torque and fast acceleration and are willing to give up top speed, go with higher gearing (lower front, higher rear)
if you like speed and going fast and are willing to give up some acceleration, go with lower gearing (higher front, lower rear)

 

will just siting here and reading and the way to do it is like you do a rear end on a car. so you take the higher nunber and / the lower so with the number you all gave in this post is
40/15=2.666
41/15=2.733
41/16=2.5625
42/12=3.5
40/13=3.076
40/14=2.857
38/13=2.923 ps not stock for raptor 40/13 is.
40/12=3.333
42/13=3.230
the higher the number the more speed lower more torque

 

Stock raptor 350 gearing is 13/38, and how does that work. In a car if you want more pickup, you run a higher gear in the rear, my stang had 4.10's in the back, and i lost top speed, this is from rmatv:
FTire / RTire / Chain / FS / RS / Battery / Spark/
21X7X10/ 20X10X9 /520X98/ 13 Tooth/ 38 Tooth /YTZ10S /DR8EA /N/A

 

its the same if you had a car so if you had 2.56 will have more top end 4.11 faster out of the hole less top end. so we have a spread of 2.5-3.5 . my and my frends raptor came stock with 13/40