Your truck weight (GVW) is the front plus rear axle, the truck axles plus the trailer axles is the CGVW.   If you weighed the trailer with no horses there was no weight in the back to "even out" the trailer load and may have made it a bit nose heavy.  Especially if your trailer has a heavy LQ.

Check and see what your axles are rated for to see if you were over their limits. 

It's not uncommon for a LT truck to exceed it's GVW while pulling a GN trailer. It however, may be within its CGVW and not exceed its tow rating.

In PA, my truck was a class 3 and I was overweight while pulling my larger trailer. By having my title changed to a "Combined" classification, my weight classification is now a class 7 which reflects the CGVW, the total weights of the truck and trailer. I'm legal to pull the larger trailer and it's within Ford's combined pulling specs. The downside is my registration fee which is now doubled.

Gard

Hi Tom ... You are correct in figuring your truck weight.  Removing the water tank from the truck will net you 200 pounds over your GVWR  ... Not a significant overload IMHO... Did you have the one horse in the front stall?  Placement of the horses will have a great effect on the hitch weight.  Horses in the last stalls will balance more of the trailer weight on the trailer wheels, less on the truck.

Dually ???  I thought you said you had a one ton truck ??  If you have a single rear wheel truck ... regardless of the badging, IMHO it's a tarted up 3/4 ton truck.  I take back what I said about 200 pounds being an insignificant  overload.  With a single rear wheel, a tire failure is a significant problem.

I believe the SRW F350 has a rear axle rating of 7000+,  tire failure shouldnt be a problem.

With "non typical" 18" and 20" tires.  My neighbour has a SRW F350 with 275/70/18 rated at 3640 @ 80 psi.

...........his doors were locked so I dont know what the rear axle rating is but I suspect its 7280. 

I remember him giving me crap about how his shiny new Ford had a rear axle capacity of nearly my GMC's GVWR (9200).

Amen, we think alike hosspuller.

Tom ... The 1/2, 3/4 & one ton series trucks are just classes of truck.  To me, it's a marketing ploy to call a single rear wheel truck a one ton truck.   Kinda like grade inflation.  A "B+" is now an "A"    

You're 600# underweight on the rear axle with a single horse in the rear stall.  What will the axle weight be when you've got three horses and a weeks worth of supplies aboard?

There are numerous tires in Load Range E that will get you over the 3500lbs per tire rating.

By steping up one size  (from 275 to 285) you can get over 4000lbs per tire, that would give you an 8000lb rating, If the axle, lugs, and wheel would handle it.

LT285/75R18 129P E/10 360420 7.5-8.0-9.5 71 19 35.1 11.6 16.3 4080 80

My next truck will be a dually if I keep my current trailer.  Like the original poster I have a F350 SRW and I am just under on the front axle, right at the max rear axle and real close to the max GCVW with 4 horses, supplies for the week and my family in the truck. Since I don't very often take the whole gang with me, Most trips I'm under. If I load the whole gang, I'm much more careful about putting anything that has any weight, in the bed of the truck. No extra water etc.

It would be nice to own two trucks, One for a daily driver/work truck and one for the horse trailer.

The big three would love to sell you one. Gm just layed off a shift in several plants because of low truck and SUV sales. Fuel prices are taking their toll.

Gard

I'll try moving the extra water tank to the rear tack.  Also, if I put in more horses, most of that horse weight will be over the trailer tires. 

I was loaded to the gills with the one horse, extra hay, cast iron pots and skillets, tons of water, wife and dogs, etc....

Thanks for all the help.

I loaded up two horses, no water/wife/dogs, and weighed the rig.  It's very interesting;

drive axle weights:

empty trailer / fuel full:  5780

1horse/water 80g/full fuel/wife/dogs:  6380

2horses/.5 fuel tank/empty water:  5840

I think the horse weight is pretty much staying over the back trailer axles.

Next I'll try water tanks full and 2 horses to see what I have...

Some weights to remember....

Water 8.333# per gallon

Diesel fuel 6.951#-7.076# per gallon, a little heavier in the winter

Unleaded Regular 6.146# per gallon

Unleaded Premium 6.263# per gallon