First off, an 11x5 is a bit too small for a 55AX. 12x7 is the lowest recommended size - Now of course you can go a little smaller, but 11x5 is small enough to make the RPM very high (Like maybe 13,000 - 13,500? But that's just a guess). In any case, you should try to prop it to get 10,500 - 11,500. Too fast and you may need to replace it years before you had intended