All the tires and wheels in the world will not fix the issues the OP is going to have trying to do what he wants to do. I tried to be cordial about it in the beginning but the buyer of that trailer should cut their losses immediately if they think adding a third single is going to help. I have preached TOUNGUE weight but a few do not seem to get the fact that the trailer pictured was never designed to be pulled by a pickup. I have personally seen the disasters. I loaded a guy here in March 2006 with a similar trailer. Once I loaded him I told him with a string of swear words to f ing lose my number. I said once he cleared the corner post of the cattle lot I never wanted to hear from him again. I stood in the road to make sure he made it out of site