Is there a way to know when they need to be replaced? I have it for less than a year with over 15k. Also what kind of tires do I buy? I know there's different types so not sure how to determine which ones are the best.

 

when the tires go bald and have no tread

 

penny trick, see how much hair is on lincolns head

but for alot of people, they just visually look at it

best tires depends on where you live, and some can go for $$$$$, i'm in socal, so sunny days and i go for something more affordable and yet decent, falken fk 452

 

All tires have wear bars built into the tread
...high spots that cross the grooves when you get down to them, you're done.