maybe it a personal thing what gearing ya run i have been riding for a couple of years and all i have run is a 14/52 but on the weekend i put on a 13 on the front. a mate said to try it .i really liked it. It put the  bike in a good rev range i thought easy to lift the front wheel but is there pros and cons. i think the bike will use more fuel. is it harder on the motor any thoughts ya all properly gone though this before .i can sit 
 on the the road in 5th cursing  on about 85 to 90 k going to track to track comfortably . it was good in the singles and on the hills .i have a 2014 450 KTM exc is there any con,s
thanks dazza 

  

I run a 50 tooth on the rear of my wr450 until it wears out, and I have a 12, 13 and 14 for the front , I just find it easier to change the front sprocket to suit  the terrain  and conditions, 

i run a 50 on the rear of my ktm 300 then i dip between the 13 or 14 tooth sprocket depending on the tight stuff or high country

Thanks i try a 50 on the back 

dazza wrote: and you will go back to what you had
52 + 14=3.71
50 + 13=3.84
52 + 13=4.00
do the math if you like the 4 to 1 ratio stick with it
I work it out  this way  you have X amount of horse power a 13 front sprocket has 6 to 7 teeth in contact with the chain any one time
to the load is shared x + 6.5  more teeth longer chain /sprocket life .
So now you know the ratio you want buy your sprockets to suite I run 15  and adjust the rear to suit rivet the chain on 2 front sprockets per chain.
my 2 bobs worth

Pick a sprocket that makes your riding easy. i.e..no clutch slipping in first gear on single tracks or climbing steep hills.

The sprocket size will make no difference to engine wear or fuel consumption for trail riding assuming you are running in the engine "sweet spot" rpm.