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07 Diplomat 40 SKQ Rear axle weight capacity

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I searched the current posts on this site for any information regarding rear axle weight limit concerns... did not find anything so appologize if this topic has been previously covered or was in a sticky that I missed...

We have just started full-timing with new to us 2007 Diplomat 40 SKQ.  With full fuel/ Water/propane and empty grey/black water tanks I am running 20,700 on rear axle and 12080 on front.

I was not smart enough at time of purchase from dealer to weigh coach to determine what the actual weights were for the axles prior to purchase.  What has me really worried is that I found a thread on IRV2 that pointed out the axles for 40 Diplomats  were Dana 19060s - which means they are only rated for 19K so instead on trying to reduce weight by 700 lbs. I need to dump 1700 Lbs from rear axle.  I do not know if that is possible even with limiting fresh water to less than 1/3 tank for traveling.

I have pulled off my bike rack & bikes figuring that the moment arm out the back would help reduce weight some... I have moved most of the heavy items/tools up to the front bay; and we are still working to eliminate anything else not essential right now to bring the weight down.  I have been running tire pressures to support the weight based on Continental's charts.

I know I should have figured this out prior to departing on the road full time... but I am still climbing up the steep learning curve here on some things.

Looking for assistance/advise on options to get weight under control/ clarification on axle weight limits -20K placard vs 19K Dana spec.

Thanks for any assistance/recommendations (I do not have capability to  trade up to tag axle at this time).








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Our rear axle is rated at 20,000. We have owned this coach for almost 15 years and are the second owner. Coach has about 110,000 miles on the odometer and has been to Alaska and back. We have always been over about 300 lbs on the rear axle and have never had a problem. We have read that, because of Federal regulations, axles rated for over 20,000 lbs will put the vehicle in a different class and RV manufactures are reluctant to use them. We have also been told that the 20,000 lbs axles may actually be capable of a weight capacity greater than 20,000.


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Our Windsor has a rear axle rating of 23K and a front of 13K for a total of 36K. For many years we were not allowed on I-90 through Ohio due to their scales. They have since waived the Federal mandate for 23K axles on motorcoaches.

It is a know fact that motorcoach manufacturers have used the same axles for a variety of coaches in the food chain. Plus there is also a safety factor built into the axles of a certain percentage. When we were Full-Tming our coach was over-loaded especially the rear axle as I was towing a 12K cargo trailer which had a tongue weight of 1800 lbs due to the way I had to load it. Traveled that way for over 8 years with three trips to Alaska and back, no problems. We no longer have the trailer as we purchased a winter home in Florida so we only tow our car now and the coach is now underweight.

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I would believe the value entered on the placard. When we bought our last motorhome (2004 Beaver Monterey), the deal was contingent on Monaco swapping out the 20,000# rear axle for a 23,000# unit. A few weeks after we took delivery we went to the factory service center in Coburg, and watched them replace the axle.

Here's the relevant part: After they replaced the axle they replaced the placard with one that had the weight rating for the  new axle. They appeared to take that placard data seriously.

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Having driven farm trucks as a teenager in Wyoming we were only allowed 20,000 lbs maximum on rear axles. I just did a search and about 50% of the states have 20,000 lb limit.  Some states allow up to 22,400. This isn't based on the vehicle's axle rating but rather what the states feel is the limit to prevent road damage. One of my friends is a Highway Patrolman  in Wyoming that was their DOT Safety Officer. He traveled around the state with portable scales setting up road side safety checks where he would weigh trucks and RV to determine if they were withing weight limits. Those found to be overweight got substantial fines. Message here is regardless of what the placard,shows, in many states the maximum is 20,000 lbs by law. If you are exceeding that legal limit and get pulled over at a DOT safety check you could be facing a significant fine.


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1 hour ago, Dr4Film said:


Motorcoaches have been exempt from the federal regulations for 20K maximum for some years now. I don't remember when that exemption took place though.





Only thing I see that supports your comment is CFR658.17.k that talks about commercial passenger bus and that expired Oct. 2009.


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Hope the tech guys can give accurate data.    My opinion based on my 2001 Diplomat and 130,000 miles; (likely dumb of me & may elicit appropriate negative comments which I accept)....  never weighed it.  I use Michelin tires and inflate to 105#.  1 blowout in front once. Out in Texas in heat.  Added Tyron bands to front.   Saw ad in current FMCA for similar product.  Have replaced all mechanical via Cummins under my floor at cost of $14,000 two summers ago.  Really.   They said coach now (then) 9 of 10.   Summary: maintenance and likely conservative weight data in original specs and my typical 62-67 speed seems ok for me. 

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Common sense....and a little understanding can go a long way.  The 20K vs 23K discussion was a popular subject and also wasted a lot of bandwidth.  I have the 23K axle.  I rarely ever go above 20K.  ONCE, I did change my loading habits and shift stuff up front and emptied my tanks and put mess (canned drinks and other heavy stuff) in the TOAD.  That was when I was going on the Ohio Turnpike in 2011.  Did not have a problem.

Quit worrying about it and have been on the Ohio Turnpike many times.  Never an issue.

As to Weight Ratings and such.  Need to understand that Monaco and Dana fritzed around with all sorts of parameters and that the weight rating is somewhat "relative".  Common sense (as well as my Engineering background" says that there is at least 20 - 30% safety factor in all the published numbers.

NOW...if you overload all the time....eventually something is gonna fail.  So....if you try to adhere to the weight ratings and keep your suspension parts (Bushings, bearings, pivots, lubrication, etc.) properly maintained.....you should not have any issues.  Tires are the same.  The placard or weight rating PSI is what is calculated for the Axle.  YES....you can put MORE air in the tires and the tires will carry a heavier load.  NOW, from the DOT standards, you are not supposed to exceed the Axle rating....so more air is just a "waste".

My advice is to WEIGH your MH.  Do it with your fresh water tank about half full and maybe your waste tanks at 25%.  Diesel tank should be around 75% full.  THAT is the normal (or at least for me) way I travel.  Don't forget your passenger load....Add in or have DW in the MH when it is weighed.  

If you are close on one end or one axle....then look at shifting your heavy items (in the cargo bins below) towards the other axle.  

My Camelot is pushing 95% on the front axle....but I have maybe 3,000 pounds unused on the rear.  I try to load the rear cargo areas heavier.  I put the lawn chairs and light and bulky items in the front bays.  When I have a full tank of fuel and a full fresh water tank, I know that I am slightly over the front axle rating.  I always run the max (115 PSI) air up front.  I might be 5 PSI lower in the rear.  I pumped up the rears once....and the ride and sway were impacted.  DW said...."What did you do?".  I stopped and fixed that.

SO....keep your tires close to or at the rated PSI's and know where your heavy items are and how that impacts your axle weights.  Keep the chassis lubricated.  Change the fluids in the rear axle and tranny as you should.

Then....Drive on....  BTW....I DO run Tyron's and a PressurePro system and I constantly monitor the pressures....especially when it gets in the 90's and I am on an asphalt highway.  I slow down some to keep from bumping up the pressure.  I typically drive 62 MPH in 65 zones and maybe 65 in 70's.  I might run close to 70 for a short time if needed....but typically way below that....

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