Axle to rear of RV distance question

10'6"

They are designed mostly based on weight. If you notice horse/living trailers have axles very far back to support the weight of the animals. They also have some crazy tongue weights. Got haulers are different too. I've always liked the axles a little farther back because it reduces sway and bouncing. But I also only buy 1 ton trucks.

Even though our 38 foot 5th wheel was built using 12 inch I-Beams they flex quite a bit more than I expected. This has resulted in a crack forming from the edge of the roof down to a large window (4 X 5 feet) which is located over the two axles on the curbside. On the other side of the 5th wheel is a 14 foot long slideout also over the axles at the front of the slideout. The rear of the slideout is within 2 feet of the rear of the 5th wheel. The crack didn't develop until the 5th wheel was 10 years old and had many many miles including a 7000 mile round trip around the US.

I think as an average a 5th wheels axles if measured from the center between the two axles, the overhang is approximately 1/3 of the length of the trailer as in a 36ft. overall length about 12 ft. of overhang 30 ft. aprox. 10 ft. this will vary some to control pin wt. but for your concerns this should be close enough.

If the frame flexes, the stresses are going to be taken up by the trailer sidewalls. If there's a slideout, any stresses will have to be taken up by the wall section remaining above and below the slideout opening. Location of the wheels depends on how the interior load is distributed. If the heavy parts of the interior are toward the rear, the rear overhang should theoretically be a bit less. It's up to the mfr. Toy haulers should have a bit less rear overhang depending on the load they can carry. On my 32' Carri-Lite (not a toy hauler), subtract the front overhang, and the axles are about centered in the remaining length, so the overhang is about 12 ft.

almost 8 and half feet. Have full master bedroom behind axles

The distance will vary per the 5er; whether it has 1, 2, or 3 axles; how long it is; the weight distribution of the front of the 5er vs. the back; etc.

Whether and how much the frame flexes depends on the cross sectional area of the frame, section modulus, the strength of the steel/aluminum used, and the weight it is carry in any given point along the frame. And frames aren't standard. This is a pretty much useless quest cause you have no way of knowing and comparing all the variables involved.

Mine is in storage and I would have to go measure it. But the length behind the axles is going to be proportional to the overall length of the 5er and the weight distribution in it. The axles must be located to balance the weight fore and aft to get the appropriate weight on the pin. Some of those 40'+ 5ers have a LOT of trailer behind the axles, but I have not seen any reports of anyone having a problem due to that overhang. I would be more concerned about tail swing on sharp turns with that much length back there.

My 5er is a 35' Montana and after 10 years, no problems on any cracking.

That is a good question. Looking forward to the answers you get. I have a TT not a fifth wheel so it may be a whole different dynamic, But I always thought there is more distance from my axles to the rear than is reasonable. So far no problems tho.

I don't know what my overhang is, I will try and remember to measure when I get home tonight but I do have a 500# boat trailer tongue snatching around on the very back of mine. I have no issues with frame flex causing any trouble. Pulled this same boat with the last fifth wheel also with no issues.