Hmmm, lets see the specs. The E rated tires have a load capacity in the 3,000 PSI range. The sticker on the door of my 3750 FL states the "dry" weight at 12,430. So to start with, we are at the maximum load range for the tire (4 Tires X 3,000 PSI each). But let's say as an owner, I put in 2,000 pounds of clothes, food, dishes, blankets, etc... Now we are at 14,430 pounds. But that is just sitting still. As we all know, as we pull the trailer, there will be "bouncing" with an uneven road.
With heavy bouncing, achieving momental inertia of 5,000 PSI on a tire is not uncommon.
Here is a short excerpt about tires:
Pacejka has developed a series of tire design models over the last 20 years. They were named the 'magic formula' because there is no particular physical basis for the structure of the equations chosen, but they fit a wide variety of tire constructions and operating conditions. Each tire is characterized by 10-20 coefficients for each important force that it can produce at the contact patch, typically lateral and longitudinal force, and self-aligning torque, as a best fit between experimental data and the model. These coefficients are then used to generate equations showing how much force is generated for a given vertical load on the tire, camber angle and slip angle.[4]
The Pacejka tire models are widely used in professional vehicle dynamics simulations, and racing car games, as they are reasonably accurate, easy to program, and solve quickly.[5] A problem with Pacejka's model is that when implemented into computer code, it doesn't work for low speeds (from around the pit-entry speed), because a velocity term in the denominator makes the formula diverge.[6] An alternative to Pacejka tire models are brush tire models, which can be analytically derived, although empirical curve fitting is still required for good correlation,[7]
and they tend to be less accurate than the MF models.[9]
The general form of the magic formula is: R(k) = d \cdot sin \{ c \cdot arctan [ b(1-e)k+e \cdot arctan(bk) ] \} \, where b, c, d and e represent fitting constants and R is a force or moment resulting from a slip parameter k.
In layman's terms, there are a LOT of forces working on a tire, causing major stress, ie. speed, weight, road conditions, lateral movement, turning torque, braking, accelerating, etc... Even the torque of the lug nuts can affect a tires performance.
Bottom line, those E tires are designed for an empty, motionless 3750FL, nothing more. Keystone is being negligent on the tire side of things, especially for their longer units. Personally, I think any fifth wheel over 35 feet and/or over 10,000 pounds, should have three axles. We love our Montana, but the tires are inefficient for it. Hello G14s!!