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Friday, April 3, 2020

Side to Side Motorhome weight balance

Got this question and thought that others may have similar problem.

Hi I have followed your postings on this forum and I own 2017 Newmar Ventana 4002. I am trying to understand and resolve an issue with my coach where I have a 1000 lb difference in weight on the front axle side to side. I have had the coach weighed on all 4 corners 3 times and get the same results. My understanding and I think it may have been in one of your post that the difference should never been more than 500 lbs side to side.

I am having a conversation with Newmar about this and pushing them for answers why as I am well under the GAVR and well under the GVWR. I have unloaded and moved the contents in the basement and inside the coach around hoping to make a difference and the reality is I don't have much to move.

I am looking for any studies or evidence that I can show Newmar that this is not safe if indeed my information is correct that side to side should not be more than 500 lbs. I am hoping you might know of something I can get my hands on or someone I can talk to.

Thank you for taking the time to read this PM.

Sincerely,  Newmar owner.


My reply:

You may have misunderstood the side to side weight comments.

It is suggested that people get "4 corner" weights rather than just axle weights, as it is known that some coaches are unbalanced side to side.
We do this because if you only get axle weights and simply divide by 2 and assume your side to side weights are even, you could end up with an overloaded or underinflated tire IF the sides are not close to even.
Not sure where the 500# figure comes from other than looking at the load increments in the tables for each 5 psi. You will see that with some large tires the load capacity can increase by a few hundred pounds with an increase of 5 psi.

I do not remember ever seeing a "should" not be more than 500# different statement

You have confirmed that your coach is not balanced side to side and it appears you have made a good effort to get more balanced but have not been able to because of the design / layout of your coach.

With that in mind, and knowing the load on the "heavy end", you need to consult the Load/Inflation tables and use the heavy end weight to learn your MINIMUM inflation for all the tires on that axle. I still recommend you add 10% to the table inflation number as long as you do not exceed the max inflation rating for the wheels. This 10% helps avoid TPM low-pressure warnings due to an occasional drop in Ambient air temperature 

I trust you have confirmed with your RV Mfg that the wheels are capable of supporting the heavy end load.
I hope this clarifies what you need to do and answers the "Why" we suggest you get the weights on each end of each axle.

##RVT942

Friday, March 27, 2020

"Reserve Load" or Load Capacity Margin

Ran across a post on Reserve Load or Reserve capacity that suggested the RV owner had been given incorrect information. Here is the post and my reply.

Personally, I'd run LTs, simply because of their higher "reserve" capacity; upwards of 30% over the stated load. Given that STs have, at best, 10% (used to be basically 0%), you're still in ST load territory, with a much better tire. Hell, we used to run our old 1/2t trucks with massive loads and just air up to 60-65 psi and go. Yes, it wasn't very far, or very fast, but those tires still lasted 50-60k miles, usually with steel cord showing around the edges. :-) We'd then take them off and put them on a disk or trailer and use them until they sun-rotted.



I think someone miss-informed you about "Reserve Load".
All tires have a stated load capacity for example. "2,340# Max Load" molded on the tire sidewall at a stated inflation level such as  "50" psi.

"Reserve Load" is the difference between the actual applied load and the stated load capacity and is many times stated as a percentage

Example: A vehicle is on weight scales and we learn that a tire has 2200# load on the tire. The tire has a load capacity of 2,750#.   2,750 minus 2,200 = 550#   which is 20% of 2,750. It doesn't make any difference what type tire we are talking about as the math is still the same.

Now, it is true that for a given set of dimensions, e.g., 235/75R15,  the stated load capacity is different depending on type tire and inflation level.   P-type and LT-type and ST-type each have different stated load capacities at their stated inflation pressure. For this discussion, let's keep inflation differences out of the picture.

Let's look at a P235/75R15 at 35 psi is rated to support 2,028# ( In a trailer application P-Type must be De-rated by Load/1.1 giving 1,842# capacity.) An LT235/75R15 is rated for 1,530# @ 35 psi and an ST235/75R15 is rated to support 1,870#

BUT the "Reserve Load" calculation is still  (Tire Load Capacity)/Measured scale Load).

The 10% margin for trailers is the difference between the GAWR and the total capacity of the tires on that axle at their max load.  I have posted in my blog some actual margins showing that many cars have load margins of 25% to 35% while some RVs made before Nov 2017, when RVIA changed the "Margin" to 10%, had margins of tire capacity vs GAWR as low as 1%.

Hope this helps.

##RVT941