OCCC, GCWR, Tongue Weight, Tow Weight

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September 13, 2018, 02:02:10 pm

I'm confused by some of the weight measurements and calculations and hope you guys can explain better than much of what I've read online.

ASSUMPTION FOR SIMPLE ME: Using 1,800 pounds OCCC (close to the 31ft LD) AND a four-wheel down toad weighing 3200 pounds(mfg spec) and a hitch rated at 4000 pounds.

What is the tow weight? (I think it is 3200)

What is the tongue weight?

What values change if I tow on a front wheel dolly and not four-down?

What do I subtract from the OCCC to determine the max weight of the people and stuff I can have in the LD? (I think it is tongue weight.)

Thanks.

John in Maryland

Re: OCCC, GCWR, Tongue Weight, Tow Weight

Reply #1 – September 13, 2018, 03:23:54 pm

John

While I cannot help you with the math... my worst subject, I can say this: I own a 2004 30'IB and have/am towing a Honda Civic and a Honda CRV for roughly 93K+ miles over a span of 14 years. I've had the coach weighed a number of times, always coming in on the sunny side of too heavy.

In that time I have not had any issues with this arrangement, it takes it in stride as long as I do my part. You, no doubt, will find the same, as long as you don't take your rock collection out on the road with you.

Re: OCCC, GCWR, Tongue Weight, Tow Weight

Reply #2 – September 13, 2018, 03:27:14 pm

Quote from: BowieJohn - September 13, 2018, 02:02:10 pm

I'm confused by some of the weight measurements and calculations and hope you guys can explain better than much of what I've read online.

ASSUMPTION FOR SIMPLE ME: Using 1,800 pounds OCCC (close to the 31ft LD) AND a four-wheel down toad weighing 3200 pounds(mfg spec) and a hitch rated at 4000 pounds.

What is the tow weight? (I think it is 3200)

What is the tongue weight?

What values change if I tow on a front wheel dolly and not four-down?

What do I subtract from the OCCC to determine the max weight of the people and stuff I can have in the LD? (I think it is tongue weight.)

Some specs you need are GVWR (Gross Vehicle Weight Rating) and GCWR (Gross Combined-vehicle Weight Rating).

GVWR is the max that the motorhome can weigh and still be within manufacturer specs for suspension, drivetrain, brakes, etc. Another thing to be aware of are the GAWRs (Gross Axle Weight Rating) for front and rear axles. It is not uncommon to be at the GAWR of one axle and under the GVWR for the entire MH. Sometimes you can move enough weight around to get around this, and sometimes not.

The amount you can tow is GCWR minus actual motorhome weight or the hitch and tow bar ratings whichever is less.

The motorhome as built is usually specified by it UVW (Unladen Vehicle Weight), which include engine fluids and full fuel.

The OCCC (Occupant and Cargo Caring Capacity) is the total weight of people and "stuff" you can add and stay under GVWR (subject to GAWR limits). I think it assumes a full propane tank.

Tongue Weight is the vertical weight on the hitch, usually a factor towing a trailer. Tongue weight for flat towing is usually miniscule (basically the tow bar weight). A tow dolly might add a little tongue weight but I would not guess very much. Most people much prefer flat towing to dolly towing. Tongue weight must be included in GVWR, and usually rear GAWR. Tongue weight usually adds to the rear axle and can unload weight on the front axle. Too little weight on the front axle can affect handling.

Getting a "four corner" weighing of any fully loaded motorhome is a good thing to do.

I hope this helps. Feel free to post more questions.

Art

Re: OCCC, GCWR, Tongue Weight, Tow Weight

Reply #3 – September 13, 2018, 05:20:32 pm

"Some specs you need are GVWR (Gross Vehicle Weight Rating) and GCWR (Gross Combined-vehicle Weight Rating)."

I don't think I've ever seen such a succinct and complete explanation of those parameters. Thanks for that!

Re: OCCC, GCWR, Tongue Weight, Tow Weight

Reply #4 – September 13, 2018, 05:26:34 pm

Following on from Art's post....
I picked up our 2013 31 IB on 4/24/2014 and took it home near Sacramento CA.
The door sticker reads CVWR 14500, GAWR (front) 5000, GAWR (rear) 9600. Gross Axle Weight Rating
I filled fuel and propane and with an empty water tank had it weighed at a moving company.
Gross weight 12660. (14500 - 12660 = 1840 for OCCC)
Front axle 4540 (Left 2360 Right 2180)
Rear axle 8120 (Left 4320 Right 3800)
At Quartzite last January I put it on a Cat Scale which read
Steer Axle 4360 Drive Axle 9380 Trailer Axle (ie towd) 3900 for a gross weight GCW 17640.
So the rig weight 13740 and the towd (2011 Honda CRV stuffed ) weighed under the LD recommended 4000 lbs tow weight.

Something to keep in mind that others have pointed out, you lose about 2% capacity for every 1,000 ft of elevation increase. What this meant in practical terms for that trip is I would technically be 'overweight' (or under powered) going home over 7,057 ft Donner Summit at Lake Tahoe on US 50. You don't want to do that much if you intend to drive it forever.

hope this helps. If you have questions about my numbers, please PM me.
Joel

Re: OCCC, GCWR, Tongue Weight, Tow Weight

Reply #5 – September 13, 2018, 08:07:41 pm

You may find the information in The Companion useful.
You might start with The Lazy Daze Companion: Towing

As mentioned above, the 4 wheel loaded weight of the LD is where you start.

For me, GCWR is the overall controlling factor. If your rig is rated for 20,000, that is for the LD and the toad. Going at highway speed on level ground is different than going up or downhill. Not much strain on level ground. The combined weight of starting and stopping were considered in coming up with the GCWR. So your brakes and transmission can be pushed when you exceed the GCWR. Especially on hills and at elevation. The GCWR is reduced 2% per 1,000 feet of elevation. This applies to ALL E450 chassis with the V10 engine.

You will find a link to Wikipedia article on GCWR.

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September 13, 2018, 02:02:10 pm

Reply #1 – September 13, 2018, 03:23:54 pm

Reply #2 – September 13, 2018, 03:27:14 pm

Reply #3 – September 13, 2018, 05:20:32 pm

Reply #4 – September 13, 2018, 05:26:34 pm

Reply #5 – September 13, 2018, 08:07:41 pm

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