Originally Posted by msquared48
It is a 4X4 though, and the owner said he had raised it by 4" which concerns me for the fifth wheel mount I have yet to purchase. I am worried about the capacity of the mount to adjust vertically, and with the 4" lift, the mount would probably have to be lower than the standard for that specific model truck, and would also have to clear the side rails of the bed during a turn, which could be a problem..
The fifth wheel hitch will not be the problem. All the major brands adjust vertically. Plus the pin box on the trailer also adjusts to raise or lower the kingpin of the trailer.
Your problem might be clearance between the trailer overhang and the top of the bed rails when the trailer is level front to rear. You want the trailer level for safe towing, so if the truck and trailer don't match, you have to either raise the trailer or lower the truck. Adjusting the hitch or the pinbox is only for fine-tuning level of the trailer when hooked up to the truck, not for changing clearance between truck and trailer.
The fix is to back the truck up to the level trailer and see how much clearance is left between the top of the bedrails and the underside of the trailer overhang. If it's less than about 5", then you'll have to either raise the trailer or lower the truck to have a level rig when on the road.
As a corollary here I am also worried the truck may have oversized tires that could also complicate the problem here, raising it even further. The tires are M+S 35 X 125.0 R18.5LT 123Q. Seems to be basically a tire for off road, possibly running in mud. I just may have to get new tires to solve that problem.
You misplaced a period in your specs, so it took me a while to realize you meant 35x12.5R18.
Those are expensive tires - about $400 each. Here's the Goodyear version:
Goodyear*Wrangler MT/R with Kevlar
And the tread is not the problem. The diameter of the 35" tire reduces the power and torque where the rubber meets the road by about 8.7%. So your 4.10 axle ratio will "feel like" a 3.74. Or if your have a 3.73 rear axle, it will "feel like" a 3.40. You will feel the difference when dragging that trailer up a long mountain pass, and your 460 gas lover will drink a bunch more gas.
So if the truck is too high to provide at least 5" of clearance for a level trailer, then you need a different truck, or spend the money to lower the truck. If you get rid of that lift and tall tires, that would probably do the trick, but not cheap. The Avion is a wonderful 5er if it has been well maintained, so I'd do something to keep that trailer and match a truck to it.
I don't know what type of suspension the Avion has, but if it is ordinary springs and shackles, then you can raise the trailer about 3" or 4" by moving the spring perches from under the axles to over the axles. That's called "flipping the axles" but you don't literally turn over the axles. Way back when, I had to "flip the axles" on a 5er to get it to tow level behind my SuperDuty. The trailer looked sorta phunny with its "high water pants", but towed great. The steps into the trailer were too high for comfortable climbing, so we added a step.