Ok, is this idea insane? Lay it on me, good and bad.

danemayer said:

When we first started researching RVs, one of the things I read about was "porpoising" where weight and balance from pinbox to axles is poorly designed. An RV with poor weight and balance design will not tow well, even on smooth roads. I'd guess that adding a 3rd axle would change the weight and balance significantly.

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G_Hage said:

As I look at, and crawl around underneath our Mount Rushmore and look at the frame, axles, and think about all that beautiful [and extremely heavy] granite throughout, I truly question if two Mor/ryde IS axles with Goodyear tires is really adequate for this fiver. I'm not sure if the GVWR of 16,000 lbs and/or the UVM of 12,580 is truly correct (actual scaled weight) or simply a calculated weight. Does Heartland actually weigh each unit to determine an accurate dry weight? Does anyone know how much additional weight the granite added to the MR, as compared to the other counter tops (corian, composite,etc) Heartland uses?

1) Heartland DOES weigh each unit separately for a dry weight NOW. I do not know what they did back when your trailer was built but I suspect they did then also.

2) Granite vs. Corian / solid surface. Although most people call any solid surface Corian; Corian is a DUPONT name brand for the first solid surface on the market. They developed it and patented it. That is why using the word Corian has become generic for all solid surfaces but there is a huge difference. Corian outweighs; per sq ft.; most solid surfaces out there. It is a much denser product than say Hanex, Meridian, Avonite etc. Corian/ solid surface can also be ordered in different thickness's depending on application which can dramatically affect weight per sq ft. True Corian ALWAYS has the gold Corian coin embedded in it somewhere on the surface.

As with Corian/solidsurface, granite has a wide range of weight per sq. ft. also. Depending on the quarry (which determines it's name e.g. Santa Cecilia , Giallao Ornamental, Venetian Gold etc. ) and the thickenss will determine actually weight. There are typically two thickness of granite-2cm. and 3cm. 2cm is rarely used (or at least shouldn't be used) in any wet application because of the abuse that typically goes along with a wet application e.g. kitchen countertops are usually used for preparation whereas a Butlers Panty is for display and serving.

So before comparing weight of granite vs. solidsurface, you have to know exactly which product you have and would want to go to.


I feel that rather than always running the current 2-axle configuration at or beyond their 8000 lbs capacity rating (if that's in fact the actual rating of the replacement axles that were put under this Fiver after the originals failed), I would be more comfortable pulling this MR with three Mor/ryde IS axles. I do not see need for the third axle to be a braking axle since the current two are equipped with hydraulic disc brakes providing the two are 8000 lbs rated.

As several pointed out already, adding axles will change the dynamics of the trailer. It will effect pin weight, stress on the frame when turning, porpoising etc etc. Probably not a good idea unless you have an engineer design the set up for you.

Looking at the slides and frame it would appear adding the third axle behind the original two could be easily done, meaning ordering the triple axle fenders, cutting the aluminum sheeting under the fender, welding the axle mounting tubular steel etc to the frame, etc.

Has anyone seen this done to the Mount Rushmore? Does it sound feasible? Or does it sound insanely out there? Knowing the history of this unit, and wanting to tow it in peace and without worry of damage from overloaded tires, etc, I feel this would be a worthwhile improvement to a very nice unit. I'm also seriously considering beefing up the ten inch I-beam on the Lippert frame by having 2x2 tubular steel welded to the bottom of the I-beam with 2x2 cross pieces (spacing yet to be engineered) from I-beam to I-beam for additional lateral strength.

Before you beef up the frame, again you might want to get an engineer involved. I believe the older LMs used a tubular frame on the drop instead of I-Beam. With any type of frame, there is a certain amount of flexibilty built into it. If you build something to stiff it could cause lots of problems down the road(no pun intended). e.g. When I was a fleet manager, we used a Ford chassis on the LT9000 becuase of it's flexibilty. With the wheel base that we speced, the frame had 33" of flex at adjacent corners and still retained it's memory. We ran about 20% off road and the flex was important.

We plan on keeping this unit a long time and for what we purchased it for, there's monetary room for such improvements.

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kakampers said:

Agree with Larry completely, in fact, after discussions with More Ryde we too decided on 7K "axles" to insure a softer ride....and it works, especially considering we run very heavy.

That makes sense. I'm hoping Mor/ryde will still have the information regarding the Mor/ryde axle assembly they shipped to Las Cruces to replace the ones that failed. They should be very familiar with this unit and hopefully can tell me which rating axles and IS springs I actually have. As you can see in the attached photos, we currently have the 16" rims with Goodyear tires. I need to look up the weight rating of the tires,as they may or may not be more than rated for the weight of our MR.

Had it weighed and every weight is within limits and with disc brakes and 17.5 tires and rims we are extremely confident in our set up...relax!!

I'm going to call Mor/ryde to also ask if there will be enough safe clearance between the tires if I replace the 16" rims with 17.5" as the axles already appear to be close as shown in the attached photo.

One other thing...noticed you said it had a ten inch I beam...if I'm not mistaken, Landmark has always had a 12 inch I beam.

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That is what I was once told by a landmark dealer regarding a comparable model year Landmark we had looked at online. As you can see in the attached photos, Our MR is built on an 8" I-Beam frame in the drop Z below the basement, and 10" I-Beam on the rest of the lower frame area. It has box tubing for framing in the bedroom/ pinbox area. I don't know if that was the norm for MR's built as 2008 models in the last quarter of 2006 as this was. Maybe this will validate or bring understanding to my concerns and ideas. My technical engineering background was spent as a residential and multi-family dwelling designer, plus designing and inspection of the construction for municipal water distribution and wastewater collection systems. I am stepping into an area of engineering I've not had a lot of experience in the past, yet I have my concerns, as all other brands we previously considered in this weight class (16K GVWR plus) were built on 12" I-Beam frames or double stacked box beam frames.

All, please then understand my questioning the choice or reason for our MR being built on the frame it was and the axle configuration it was originally designed and built with.

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