What’s all the Fuss
about Knowing GVWR, GCWR, and GAWR?
Last updated March 4, 2006
I always get a kick when I'm out with the kids "window
shopping" (they love to look at new RVs and it's a
Take a closer look and inside you'll see the custom Trail
Master conversion package that includes quad flexsteel leather captains chairs,
TV/
I’ve got a family of 6 that includes two teenagers who are larger than most adults and a dog who weighs as much as a teenager. The Suburban is designed to carry a boatload of adults in comfort, so that’s still no big deal, right? Wrong.
What the salesfolks don't know is that I've made several trips to the local certified scale to get my actual weights in several configurations, both hitched and unhitched. In fully loaded mode (canoe on top, full 44 gal gas tank, firewood and other cargo behind the 3rd seat, and the ENTIRE family and on board), my Burb checks in at 3360 front axle, 3640 rear axle, for a total of 7000.
Since my GVWR is 7300, I only have 300 left for trailer tongue weight, WD hitch, and sway bars. Yup, 300, before I exceed GMs rating. WHOA!!!
Add our T-160 into the equation filled to the max (full fresh/hot tanks, six 5 gal drinking/cooking water containers, dual ice chests, along with food, supplies, and clothing for 2 weeks dry camping) and my axle weights check in at 3340 front, 3940 rear, and 2720 for the trailer. That means my combined gross is 10,000. Hey, not too bad since my GCWR is 12,000. I've got plenty to spare, right? Wrong.
Adding my front and rear axle weights totals 7280. I'm only
20 away from exceeding my GVWR. WHOA!!! Comparing my rear axle 3940 to my 4000
RGAWR, I'm only 60 away from exceeding my RGAWR.
At least I'm still within my Fun Finder specs of 3000 GAWR and 3190 GVWR. I actually use 3500 as my working GVWR, since my Atwood tongue is stamped for 500 Tongue/3500 Gross Weight Rating, my Leland Frame is rated to 3500, and using the calculation of 3000 GAWR (the Axle Weight Rating of my AL-KO Kober Axle) + 500 GTWR = 3500 GVWR, makes more sense to me. My tongue weight is 280, well within the 500 of my Atwood Tongue. I'm not using any WD apparatus or sway control, so no worry about additional weight there.
Another huge consideration on my part is where we live and where we like to travel to camp. Living at 5000', I'm already losing up to 20% of my V8 gas engine performance. By the time I reach 10,000' and some of our favorite camping spots, my poor V8 is only 40% of itself.
See: http://www.popuptimes.com/archives/ruleofthumb.shtml for info on Engine Performance Degradation Due to Altitude.
However, when we visit places that are at 1000' altitude or even sea-level, I have all the performance in the world pulling our little T-160 around. It doesn’t even feel like the trailer is behind us. What a difference a few thousand feet makes in tow vehicle performance!
So many times, it's just too easy (or too lazy) to quote widely advertised tow capacity (Max Trailer Weight) numbers or rattle off generally accepted "guidelines" or "rules of thumb" because these are so readily available and promoted. The most knowledgeable RVer obtains and follows GCWR, GVWR, and RGAWR for THEIR INDIVIDUAL TOW VEHICLE and TRAILER COMBINATION. They also factor the performance fallout at altitude (of course, turbo diesels don't get altitude sickness) and may also include an additional margin just for safety and comfort. The key again is knowing and understanding the details.
Here are mine:
2002 T-160 Certified Weights (all obtained at Agland scale)
Empty (Unloaded) Weight--UVW New from the Dealer (13” rims/tires, 2nd battery, Skid bars, Full propane tank):
180
Dry (Loaded) Weight--Minimal Loading (14” rims/tires, Permanent Cargo and Supplies including Non-Perishable Food, Empty Tanks, Empty Fridge, Empty Rolling Ice Chest, Full 5 gal Drinking Water Container):
220
Wet (Loaded) Weight--Typical Loading (Full 24 gal Fresh/6 gal Hot Water Tanks, Full Fridge, Full Rolling Ice Chest, Perishable Food, Duffle Bags of Clothing):
260
Max (Loaded) Weight--Maximum Loading (Two Extra 5 gal Drinking Water Containers, Two Extra 5 gal Fresh Water Jugs, Second Full Ice Chest):
280
Note:
Original Rims/Tires: 13” Loadstar K550 Load C - 1360lbs at 50psi, 80 lbs lug nut torque
Replacement Rims/Tires: 14” Goodyear Marathon Load C - 1760lbs at 50psi, 100lbs lug nut torque
1998 Suburban K1500 Ratings:
3600 FGAWR, 4000 RGAWR, 7300 GVWR, 12000 GCWR
Suburban--Maximum Loading Unhitched (44 gal Gas, Family, Canoe, Canoe Gear, Two Full 5 gal Fresh Water Jugs, Firewood, Dog Food):
3360 FGAW, 3640 RGAW, 7000 GVW
Suburban--Maximum Loading Hitched to Maximum Trailer Loading:
3340 FGAW, 3940 RGAW, 7280 GVW
Entire Rig--Maximum Loading Hitched:
3340 FGAW, 3940 RGAW, 2720 GAW, 10000
Liquid Weights:
Water = 8.3 lb per gal.
Gas = 6.1 lb per gal.
Diesel = 7.1 lb per gal.
Propane = 4.5 lb per gal. (can be as little as 4.2 lb per gal. as actual weight depends on temperature)
So What Are the
Actual Formulas to Use?
1. Tow Vehicle GCWR minus Tow Vehicle Scale Loaded Weight equals Max Trailer Weight.
In my case: Suburban 12000 GCWR minus Suburban 7000 Scale Loaded Weight equals 5000 Max Trailer Weight.
2. Tow Vehicle GVWR minus Tow Vehicle Scale Loaded Weight equals Max Trailer Tongue Weight.
In my case: Suburban 7300 GVWR minus Suburban 7000 Scale Loaded Weight equals 300 Max Trailer Tongue Weight.
Note: If a Weight Distributing Hitch and/or Sway Equipment is used, then the weight of these items must be included in the Max Trailer Tongue Weight.
3. Tow Vehicle RGAWR minus Tow Vehicle Scale Loaded Rear Axle Weight equals Max Rear Axle Loading.
In my case: Suburban 4000 RGAWR minus Suburban 3600 Scale
Loaded Rear Axle Weight equals 400 Max Rear Axle Loading.
Since my Max Rear Axle Loading is Greater
Than my Max Trailer Tongue Weight, I do
not need to use a Weight Distributing Hitch.
However, if my Max Rear Axle Loading happened to be Less Than my Max Trailer Tongue Weight, I would need to use a Weight Distributing Hitch or if possible, move
cargo out of the Suburban and into the trailer to redistribute weight manually.
One Final Caveat
Even though I’ve figured a Max Trailer Weight for my situation of 5000, I cannot, CANNOT, exceed either the 300 Max Trailer Tongue Weight or 400 Max Rear Axle Loading figures that I’ve calculated. Since most trailer tongue weight percentages run 10-15%, using the minimum 10%, my Max Trailer Weight would really be limited to 3000. If I were to move 100 lbs. of cargo out of the back of the Burb (carry it in the trailer for example), I could increase my Max Trailer Tongue Weight to 400 and my Max Rear Axle Loading to 500. In that case, I could probably safely handle a trailer up to 4000 in weight (if the tongue weight percentage was 10%).
In the case of the Fun Finder T-189DD (.doc Word format) floorplan I’ve proposed, this is exactly what I would need to do. Empty scale weights posted by owners of single axle, aluminum-sided, A/C and Awning equipped T-189FDs (see Yahoo! Shadow_Cruiser_Fun_Finders messages #1151 and #3004) are just under 2800. I estimate that with an additional 8” in length and dual batteries and a 30lb LP tank on the tongue, my empty T-195 would weigh in at just under 3000. Figuring in the max 1000 of water and cargo loading we currently do, I’d be just under a 4000 Max Trailer Weight. And since we travel frequently to 10,000’, that’s the most I’d EVER want to tow with our Burb. Now, if GM would introduce the Duramax/Allison in the Suburban/YukonXL……
Ultimately, in my current situation with our T-160, the way I load our Suburban limits my Max Trailer Weight to the actual max 3000 Scale Loaded Weight of our T-160. And thus, “…a little 16' 3000 trailer just brought the mighty Burb to its knees.”