I am building a new trailer to haul my equipment. I currently have a 16 ft that is just a little too short so instead of trying to modifly it I decided to build a 18 ft'er. My question is how far back from the tongue do you place the axles so it will pull right and have good weight distribution. I will be using two 3500lb axles with brakes and springs. There should be a formula for figureing the axle placement but I havent been able to find it.