How does Keystone figure their GVWRs

[BiggarView]

Can anybody explain how Keystone came up with their Montana GVWRs.

As an example the 3811MS reported specs are 16750 GVWR. curiously the UVW is 13595, the CCC 3155 equalling 16750 but, the stated pin weight is 2750 and the rated axles 7k each or 2750+7000+7000= 16750.

I find it odd that both methods equal 16750. SO where did the 16750 come from exactly. The Sailun tires should not be a factor since they are rated over 4k each at 110 PSI. So where is the weak link that is holding down the GVWR? MY best theoretical calculation from engineering types I have spoken to say it should be 17500 which would consist of the 14k of axle rating, and 25% of that as maximum pin weight or 3500 lbs thus 14000+3500=17500. It feels like Keystone simply came up with an arbitrary GVWR number, weighed the trailer and subtracted that weight from the apparently arbitrary 16750 to come up with the CCC. the first method takes an actual known weight and adds a seemingly capricious CCC number to it to come up with the GVWR and the second method takes a known unloaded trailer pin weight and adds the rated axles to it. What gives. A GVWR should consist of all ratings, axles and frame and tires and limits by the weakest links in each part, not taking what appears to be known weights and then adding or subtracting from an unknown number.. So how do they determine that number? My best guess is they took the UVW subtracted the pin weight (13595-2750=10845... then since the axles are rated for 14000 and the UVW axle load is 10845 then that leaves 3155 CCC therefore they added the 3155 to the UVW of 13595 to equal 16750. AM I wrong? This does not make sense to me as nobody loads a trailer without putting weight on the front of the trailer. This is why I feel the 17500 GVWR estimate is more appropriate.

Inquiring minds want to understand. Especially in light of the idea of adding upgrade axles and tires ALA MOR/Ryde IS 8k and H rated tires. (Both of which add about 880 lbs of unsprung weight to the trailer but also add capability to the trailer)

[PNW Fireguy]

Regardless of what is added the sticker indicating the weight limits is what the LEO looks at and takes into consideration.

[BB_TX]

Originally Posted by BiggarView

Can anybody explain how Keystone came up with their Montana GVWRs.
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Inquiring minds want to understand. Especially in light of the idea of adding upgrade axles and tires ALA MOR/Ryde IS 8k and H rated tires. (Both of which add about 880 lbs of unsprung weight to the trailer but also add capability to the trailer)

Being an engineer myself (retired), ratings of any significant product are based on engineering design calculations and often computer modeling to meet specific final product specifications, not on weighing, measuring, or otherwise determining the rating upon a finished product. It is typically designed, built, and then verified to meet the initial design criteria. Even if the tested numbers somewhat exceed the specifications they will probably stick with the design numbers. Thus the even, balanced numbers.

How exactly Keystone or any other RV manufacturer accomplishes that would probably be an in house secret.

[BiggarView]

I'd pay extra for 8K axles from the factory. It would solve a lot of problems. I also saw on a Keystone video recently the rep make mention of working with the customer on an upgrade through MORryde. Just talk? If real, would adding the 8k IS truly raise the GVWR and CC numbers on a factory build before it rolls off the production floor?

[AZ Traveler]

Biggar,

The easier option is to just buy a rig with a larger GVWR if that is what you need. Jayco and Mobile Suites among others have heavier models.

[PNW Fireguy]

Originally Posted by AZ Traveler

Biggar,

The easier option is to just buy a rig with a larger GVWR if that is what you need. Jayco and Mobile Suites among others have heavier models.

Yup, that’s the ticket

[BiggarView]

Originally Posted by AZ Traveler

Biggar,

The easier option is to just buy a rig with a larger GVWR if that is what you need. Jayco and Mobile Suites among others have heavier models.

Jayco has a similar floor plan to the 3811MS but the CCC is similar too and there are some features we just do not like with their 2020 updates. DRV has no floor plans that we really like and they are also way out of our budget. We love the 3811MS plan but are concerned about the CCC. Just don't know if it is enough. seems everybody measured the weight of their gear differently, some include the weight of everything and others just their personal gear. Getting a handle on that would also help determining what will work or not.

[BiggarView]

Originally Posted by AZ Traveler

Biggar,

The easier option is to just buy a rig with a larger GVWR if that is what you need. Jayco and Mobile Suites among others have heavier models.

Also, a heavier GVWR does not necessarily translate into more CCC.

[Richcart]

When I was doing my research on 5th wheels, we liked the Montana product but I wanted more capacity. I contacted them and asked if we purchased the Montana and added 8000 axles and upgraded the suspension could the capacity be increased? They said no. As mentioned, they will stick to the listed weights regardless of what the customer does.

[BB_TX]

Axles are simply one component. If the trailer was designed for 7,000 lb axles, then the springs, the frame members to attach the suspension members, and possibly the location of the suspension would be based on those 7,000 lb axles. Changing to 8,000 lb axles would require re-certifying that design, or possibly beefing it up for the additional weight rating.

[Todd727]

Of course the weights add up. They have to. The way they figure the CCW was to take the GVWR and subtract the empty weight.

Axle weight rating is defined by Dexter (or whoever built the axles), so that's where the 7000 x 2 comes from. They understand that you will have some weight on the pin, so they don't have to limit the GVWR to 14K.

They used a conservative 16.5% pin weight to make that increase and rounded it off to an even 16750. It's the same reason my gooseneck equipment trailer with two 10K axles is rated for 25K pounds. I have to plan on having 5K on the pin.