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Open Roads Forum  >  Dinghy Towing  >  General Topics

 > How To Calculate Tow Capacity

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DallasSteve

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Posted: 01/09/20 09:23pm Link  |  Quote  |  Print  |  Notify Moderator

I did a quick search and I didn't find a thread like this so here goes. I'm looking at a smaller Class A gas motorhome. It's what I like to call a Class A minor (for the musicians out there). I eventually want to flat tow a car behind it; probably a Jeep Wrangler. I've read that part of the calculation depends on how much weight is loaded in the motorhome and in the Jeep so I would need to take them to scales after they are loaded. When I have that information what is the formula to be sure I can safely tow the car? I know the 4 door Wrangler weighs a little more than the 2 door and I've read most motorhomes can tow a Wrangler, but I want to be sure before I buy the vehicles. Below are the specs for the model I am looking at.

GCWR (lbs.) 23,000
GVWR (lbs.) 16,000
GAWR - Front (lbs.) 6,500
GAWR - Rear (lbs.) 11,000

Trailer Hitch 5,000-lb. drawbar/500-lb max vertical tongue weight

* This post was last edited 01/10/20 08:52am by DallasSteve *   View edit history





rk911

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Posted: 01/09/20 10:10pm Link  |  Quote  |  Print  |  Notify Moderator

first, you are wise to realize that there are limits and for seeking advice.

before you buy a toad you need to know what your mh weighs as it is loaded for a trip. that includes full fuel, fresh water and lp tanks, food, clothing, supplies, pets and people. get separate axle weights to make sure that neither axle is is overloaded. then apply the three tests above. for every pound your mh exceeds its gvwr you lose a pound of available tow weight.

the amount of weight you can safely tow will be the lesser of the following:

- the gross combination weight rating (GCWR) of the MH minus the actual weight of the MH as it is loaded and configured for travel. actual or rolling weight is determined by loading the MH as you would for a trip. fill the fuel, fresh water and LP tanks. add clothes, food, supplies, etc. don't forget people. find a scale and get individual axle weights at a minimum. compare the actual axle weight to the axle weight rating (GAWR) for that axle. each axle will have a different weight rating. provided that neither axle is overweight for every pound your mh exceeds its gross vehicle weight rating (GVWR) you lose a pound of available tow weight. don't guess or assume...know.

- the weight rating of your hitch. the amount of weight your hitch is engineered to carry should be in your owner's manual.

- the weight rating of your tow bar. check the specs of your tow bar if you already have one. if not i'd look for one that is capable of towing 8000-10,000 lbs.

good luck.


Rich
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DallasSteve

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Posted: 01/10/20 08:48am Link  |  Quote  |  Print  |  Notify Moderator

Rich

Thanks for the reply, but I'm still confused. Is the GVWR (16,000) the empty weight and GCWR (23,000) the maximum load including the toad? So if I weigh the motorhome and it's at 17,000 then I have 6,000 load left (23,000 - 17,000), right? But since the hitch max is 5,000 I still can only tow 5,000 (if I have a tow bar rated at least 5,000), right? So if the Jeep loaded is under 5,000 I'm OK? But if the motorme loaded was 18,500 my max load remaining is only 4,500 (23,000 - 18,500) and that would be the limit that I could pull as a toad, right?

But then my confusion is how does the front and rear GAWR figure into this? In this case they total 17,500 (6,500 + 11,000). Can somebody please explain?

rjstractor

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Posted: 01/10/20 12:18pm Link  |  Quote  |  Print  |  Notify Moderator

DallasSteve wrote:

Rich

Thanks for the reply, but I'm still confused. Is the GVWR (16,000) the empty weight and GCWR (23,000) the maximum load including the toad? So if I weigh the motorhome and it's at 17,000 then I have 6,000 load left (23,000 - 17,000), right? But since the hitch max is 5,000 I still can only tow 5,000 (if I have a tow bar rated at least 5,000), right? So if the Jeep loaded is under 5,000 I'm OK? But if the motorme loaded was 18,500 my max load remaining is only 4,500 (23,000 - 18,500) and that would be the limit that I could pull as a toad, right?

But then my confusion is how does the front and rear GAWR figure into this? In this case they total 17,500 (6,500 + 11,000). Can somebody please explain?


This weight questions are actually pretty simple and often overthought. Your GVWR (stands for Gross Vehicle Weight Rating) of 16000 pounds is the maximum loaded weight, not the empty weight, of the motorhome by itself. The GCWR is the maximum weight of the motorhome and trailer (or tow vehicle) combined. So doing the math, when fully loaded the motorhome can still tow 8000 pounds. But all of this math is basically irrelevant, because the motorhome hitch is only rated at 5,000 pounds. That's the maximum weight the motorhome can tow because in this case the hitch is the "weakest link". Tongue or hitch weight does not really factor into the equation in the case of four-down towing because the motorhome only carries half the weight of the tow bar itself, probably 50 pounds or less.

So, as far as towing a toad goes, this motorhome can handle any that weighs less than 5,000 pounds. But a bit of unsolicited advice, make sure that the motorhome itself has enough payload capacity to handle the weight of passengers, water, food, beer, and anything else you plan on loading into the motorhome. Personally I'd look for a motorhome with at least 2,000 pounds of payload capacity.

DallasSteve

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Posted: 01/10/20 02:19pm Link  |  Quote  |  Print  |  Notify Moderator

rjstractor

Thanks for the reply. You say I should look for a motorhome with at least 2,000 pounds of payload capacity. How can I determine that from the 6 numbers they gave me? Maybe I can't. If GVWR is the maximum weight of the motorhome with contents I need to know the empty weight to know its payload capacity. I thought GVWR was the empty weight, but apparently it's not, so I don't seem it in those numbers. Unless they tell me that number I would need to weigh the motorhome to know what the empty weight is. Will the dealer have a scale?

Walaby

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Posted: 01/10/20 05:29pm Link  |  Quote  |  Print  |  Notify Moderator

GVWR pretty universally means Gross Vehicle Weight RATING.. Which translates to the max weight the vehicle can weigh with all the cargo, passengers, etc...

Yes, so you need to know the empty weight. I would have thought that would be available on a sticker, like trailers. Is there an abbreviation on the sticker that says UVW? Which stands for unloaded vehicle weight?

Mike


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DallasSteve

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Posted: 01/10/20 07:52pm Link  |  Quote  |  Print  |  Notify Moderator

Mike

I copied the other numbers from the specs in the manufacturer's brochure. There is no UVW in the brochure nor on their website. I have an email for their customer service. Maybe I will write them and ask.

Steve

rjstractor

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Posted: 01/10/20 07:55pm Link  |  Quote  |  Print  |  Notify Moderator

Yes, there is usually a sticker that lists the UVW (unladen vehicle weight). But even those are not always accurate, since it will not include anything installed after the coach left the factory. The dealer probably won't have a scale, but as part of a test drive if you are serious about buying you can take it to a truck stop where they will have a certified scale. And 2,000 pounds of minimum payload is just my personal preference, many have gotten by with less and some need more.

rk911

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Posted: 01/11/20 05:32pm Link  |  Quote  |  Print  |  Notify Moderator

DallasSteve wrote:

rjstractor

Thanks for the reply. You say I should look for a motorhome with at least 2,000 pounds of payload capacity. How can I determine that from the 6 numbers they gave me? Maybe I can't. If GVWR is the maximum weight of the motorhome with contents I need to know the empty weight to know its payload capacity. I thought GVWR was the empty weight, but apparently it's not, so I don't seem it in those numbers. Unless they tell me that number I would need to weigh the motorhome to know what the empty weight is. Will the dealer have a scale?


back in the day (we've been RV'ing since 1986) when i would read reviews of motorhomes there were just three wights/ratings to consider:

- empty weight: as delivered to the dealer. minimum fuel, no water or lp
- wet weight. full fuel, water and lp
- payload. the difference between the GVWR and the wet weight.

all three must be done by individual axle weights since it very possible to be under the GVWR and still be overweight on one axle, usually the rear.

but how to get these weights especially if the dealer or owner won't let you take the vehicle to a scale before purchasing.

one way is to calculate the weights. if buying new contact the mfg and request the build sheet. that will include all options and give you axle weights. if buying from a private party you can do the same thing on the assumption that the owner has removed all of his property. then...add 6-lbs per gallon for water, 8.4 lbs per gallon for gas (7-lbs per gallons for diesel) and 4-lbs per gallon for LP. most of that weight will be on the rear axle. this will get you in the ballpark and give you a rough idea of your payload.

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