I Need A Little More Clearance

I was looking for a cheap way to get a little more clearance on my 1999 Dakota. I was wondering what is the biggest tire you can put on a 99 dakota with the factory 15 inch alloys and will it make a difference with bigger tires?
Thanks

i think its 16s but its not gonna make that much defrence i drive my 95 dodge dakota with total stock on 15s offroading all the time and i got no prob the drivers the best peice of machinery you can have