Originally Posted by 2airishuman
a 2 INCH difference front/2/back may be golden...
but it is significantly UNLEVEL and will result in UNeven loading of the tires and brakes...
and the axles which may have already settled significantly in 20 years.
looking at the profile of a 34 a 2 inch variance is obvious and too much.
A 34' A/S has a 31' body, and three axles on 30" centers. with 60" from the front to back axle (5 feet) the axles cover 1/6th of the length of the body of the trailer. Therefore, the maximum 2" difference across the entire body represents a 1/3" difference from the front to back axle (or 1/6" difference between adjacent axles). Remember, a 2" variance means the nose is up 1" and the tail is down 1" from level.
With 7000 lbs dry weight, minus 800 lbs tongue weight, 6200/6=1033 lbs per wheel. With this low loading, a 1/6" difference between the axles is a non-issue, given the axles will take half the difference. A back of envelope calculation shows the rearmost axle would be taking about 2.6% higher load than the front - less than the difference induced by running on wet road. The difference in braking effort - less than that. In this application, uneven brake effort requires either lack of traction or a different rotation speed - certainly greater than the likely difference of a new tire next to a partially worn tire - which is the sort of height difference we're talking about. This worst case is about 12 lbs load difference from the front to back axle, and assumes very very stiff suspension.
Remember, I said "up to" - I'm guessing it'll end up with an arrangement where you have less than 1/2" difference front to back. On that length of trailer I'd be looking for less than 1" front to back. As I said in my previous post, I'd consider it "safe" to tow at 2".
This raises the question why this trailer has three axles instead of two when two would carry the weight and three axles introduce tire wear problems? Distributing shock loads across three more lightly loaded axles reduces transmission of shock energy to the very long frame by one third, allowing them to keep the frame weight down, and to use the standard shell design without heavy reinforcements, while also keeping the center of gravity low. Plus the lovely handling characteristics.