I have a 1990 18.4 Grumman on a Shorelander Trailer with a 90hp Force and I bought it brand new and it had A78-13 ST on it and I had to replace them for they were shot. Couldn't find A78-13 and the ST165/80D13 which is supposed to be the cross reference which is still out there but hard to find only found them on the internet. Local dealers are telling me that they can't get the 165/80D13ST either and that I should go to the ST175/80D13 because they are and will be easy to get down the road. So I did and I had to use a screwdriver to help get it past the fender in order to get it on. Tire is hitting on both sides of the fender and hardly no clearance on top. So I thought of putting a 1" steel block in to drop axel down but I think that will give me clearance at the top and I can roll down the road with it but if i need to change a tire out I think it will still be a tight fit on the sides of the fenders getting the tire on and off. At this point I don't know what to do should I change the fenders or try to get 165's or what? Thanks hope someone can lead me in the right direction.