Right now I have a set of 22x8x15 MT et slicks..

This is a crx with a boosted B16 that im planning to get 300whp out of and im using a JDM YS1 trans with the insane low gearing.. What size slicks should I get since the gearing is so low..

I am going to get M&H slicks but I dont know a size to get and if I should use a 15" or 13" rim for them..

 

theres plenty to choose with a 13" rim size. And you get more sidewall with a 13" anyways which gets you more bite on the slick.

I'd look into a 24.5x8.5x13 M*H slick

 

as Will stated above...I would use a 13" rim the extra sidewall will benefit greatly over the 15" version. The 24.5 13's are a nice setup.

Chris