Hope all goes well mate, you are one very patient man... NT01 max size is 18" I would look at the NT05 for your 20's. I have been very happy with these, they still lose traction from low speed boosting it however from a roll on they hook up quite nicely.. If you really serious, check out the NT05R or NT555r. I believe they have options in 20's. Don't know how they would go in the wet though, however seems the guys in the US think they ok?