glanced thru the searches, but didn't see anything on how to determine what my pin weight is. I know I have to use scales, I guess truck scales, but how do I go about determining this? Do I weigh my truck alone, then hook up the fiver and weigh again? If so, how does that reflect my pin weight? It would seem that would only give me the difference between the two.Circumstances are that over the last three months, I have had slipped belts on my rear tires, first one, then the other even tho they only had 30k miles on them. Shop manager said that the tires I have normally get about 40-45k miles before something like this happens and when I told him I have a 5th wheel, he suggested that I might be running without max air pressure. Since I don't do that, I was thinking that perhaps I've got too much pin weight and I have never weighed the rig.Interested in any comments. thanks

Think of it as a load. The total weight of a load is identical to the weight bearing down on all load supporting places. 2000 pounds on the pin, plus 10,000 pounds on the wheels will make a load 0f 12,000 pounds.Weighing the truck without the pin weight, then the truck with the pin weight will determine the pin weight by itself.

Artum Snowbird wrote:Think of it as a load. The total weight of a load is identical to the weight bearing down on all load supporting places. 2000 pounds on the pin, plus 10,000 pounds on the wheels will make a load 0f 12,000 pounds.Weighing the truck without the pin weight, then the truck with the pin weight will determine the pin weight by itself.Still a little confused, how do I determine just the pin weight? In other words, how do I determine how much weight is on the pin and how much of the total weight is on the fiver wheels? Do I just weigh with the rear wheels on the scales?

when you go to the scales (e.g. CAT truck scales) there will separate scales in a row adjacent to one another. First you weigh the truck by straddling 2 of the scales so your front tires are on one and your rear tires are on the separate adjacent one. This will give you separate weights for the front axle (called 'Steer Axle' on the weight ticket) and the rear axle (called 'Drive Axle on the weight ticket). Now, hook up to your trailer and go back onto the scales so your truck front axle is on the first scale (as before), your truck rear axle is on the second scale (as before) and your trailer axles are both on the third scale. You'll get another weight ticket that will now show the Steer Axle, Drive Axle and Trailer Axles. To get your pin weight take the difference between the Drive axle weights with and without the trailer hooked up. There may also be a difference in the Steer axle weights that you'll have to take into account based on whether the Steer axle weight went up or down with the trailer hooked up vs. not hooked up. Also, you can do a web search that will give you info on how to do it and show you what a weight ticket looks like.

Here is a description of how to weight on CAT scales.Catscale.com/how-to-weigh

If you tow a FW, it would be good to rotate tires more often. The added pin weight, no doubt puts more stress on the rear tires.As long as you are within your RAWR/tire rating, and keeping tire pressure at the max, you should not be having belt trouble.IMO, I would switch tire brands, but you do need to weigh, to be sure you are not pushing the tire load limits.Jerry

determining pin weight | Good Sam Community

43 Replies

JIMNLIN
Explorer III
Apr 26, 2014
BF Goodtrich All Terrain T/A, LT245/75R16, Load Range E, not OEM, with 90K+ miles, it's my second set of these tires.

I prefer these tires because I mostly use my truck for hunting and I need the traction for the 4 wheel drive when I get in a bind.

Hmmm, good tires.
My son keeps BFG ATs on his '02 2500 Dmax/A crew cab 4x4 truck as he hunts and fishes the FL swamps/intercoastal. He uses the LT285/65-16 E pulling a 34' BH 5th wheel trailer and his 26' blue water boat. The BFG AT's are popular over on the TC forum also however most use the larger sizes for more load carrying capacity from those heavy TC's.
Cajun_Bill
Explorer
Apr 26, 2014
JIMNLIN wrote:
op says wrote:
And no, I don't know my rear axle recommended limit cuz I don't see it in the book.

The 2500 GM Dmax/A has a 6200 RAWR which is on your drivers side door post. Your loaded rear axle weight is 5460 lbs which is 740 lbs under. Looks like a good match there. This is your biggest safety concern.

The whole purpose of this exercise was to see if possibly, maybe, sorta kinda, could my pin weight be causing the belts on my rear truck tires to slip? and yes, I always pull the fiver with max pressure (80 psi) in the rear tires.

If hauling 740 lb under the capacity of those tires was the culprit then just about every hauler out here on the roads would be coming up with slipped belts. Its not happening.

IMO its more about the tire brand/size/proper load range/speeds and pressure over the life of the tire.
Are they the OEM tires ??

What brand/load range/size/tread type are we talking here. Lots of unknowns makes for lots of guessing.

BF Goodtrich All Terrain T/A, LT245/75R16, Load Range E, not OEM, with 90K+ miles, it's my second set of these tires.

I prefer these tires because I mostly use my truck for hunting and I need the traction for the 4 wheel drive when I get in a bind.
JIMNLIN
Explorer III
Apr 26, 2014
45Ricochet wrote:
Boy I'd love for Jimnlin to hit me, kind of like hitting the lotto in civil court
:B

Jeez... here we go again with the famous RV.net myth and just your opinion.

Most trucks on the road carry weight per their certified axle/tire load ratings. Maybe one will hit you Rick and you can find out how how the system actually works. I'm sure other ambulance chasers like you have thought the same. Carry on with your non sense. :B
45Ricochet
Explorer
Apr 26, 2014
Boy I'd love for Jimnlin to hit me, kind of like hitting the lotto in civil court
:B
JIMNLIN
Explorer III
Apr 26, 2014
op says wrote:
And no, I don't know my rear axle recommended limit cuz I don't see it in the book.

The 2500 GM Dmax/A has a 6200 RAWR which is on your drivers side door post. Your loaded rear axle weight is 5460 lbs which is 740 lbs under. Looks like a good match there. This is your biggest safety concern.

The whole purpose of this exercise was to see if possibly, maybe, sorta kinda, could my pin weight be causing the belts on my rear truck tires to slip? and yes, I always pull the fiver with max pressure (80 psi) in the rear tires.

If hauling 740 lb under the capacity of those tires was the culprit then just about every hauler out here on the roads would be coming up with slipped belts. Its not happening.

IMO its more about the tire brand/size/proper load range/speeds and pressure over the life of the tire.
Are they the OEM tires ??

What brand/load range/size/tread type are we talking here. Lots of unknowns makes for lots of guessing.
jaycocamprs
Explorer
Apr 26, 2014
Cajun Bill, in your case you want the rear axle load. This will be the loaded axle weight. Divide by 2 and check against the tires load capacity.
Cajun_Bill
Explorer
Apr 25, 2014
RCMAN46 wrote:
Cajun Bill wrote:
Okay sports fan, OP here. Got 'er done this morning.

Truck only:

steer axle 4400
drive axle 2920

total weight 7320

truck and fiver:

steer axle 4220
drive axle 5460
trailer axle 9720

total weight 19400

Note: people weight--driver 275 lbs. (no derog comments please)
gray and black tanks empty, fresh water--approx 15 gallons
fuel tanks 1/2 full (13 gal. diesel)

Other info---according to my truck manual, GCWR is 22,000 lb, so my 19400 is well within limits. Max trailer weight according to manual is 14,200 lbs and at 12,080, that gives me over 2k more carrying capacity and since the trailer has almost everything I normally carry except groceries and clothes. The most passenger weight I might have is an additional 460 lbs.

Now, what is my pin weight? 5460-2920= 2,540 lbs.???? And if that is close, am I within limits?

Your true pin weight is 2360.

You have a truck on the scales that weighs 7320 (4400+2920)
Now imagine the truck is still on the scales and you lower the trailer pin on to the truck. Now the truck weighs 9680 (4220+5460) You had to add 2360 to get the truck to weigh the 9680.

Believe what you want but your actual pin weight is 2360.

Your pin percentage is pin/trailer. 2360/12080=.195 or 19.5%. A little low for a 5th wheel to handle well and not chuck.

Your hitch must be a couple inches behind the centerline of the rear axle or there was no driver in the truck during the second weighing.

This is why it is important to know actual pin weight.

Another way to look at this. Truck and trailer weighs 19400 and the truck weighs 7320. That means the trailer weighs 12080.
The trailer axle weight was 9720. Pin =total trailer-trailer axle.
12080-9720=2360.

But to be accurate there can be no loading changes between weighing's. The same people, fuel or anything else has to be in the truck both times.

OP here. The hitch is located just slightly ahead of rear axle on truck. Everything essentially stayed the same, (maybe burned a gallon of diesel going get the fiver) and I was on the scale in both instances (on the steering axle part of the scale in both instances).

So lets assume the pin weight is 2360, not 2540 as I calculated. 180 lbs. is no big deal IMHO. If it's 2360, am I within limits? And no, I don't know my rear axle recommended limit cuz I don't see it in the book.

The whole purpose of this exercise was to see if possibly, maybe, sorta kinda, could my pin weight be causing the belts on my rear truck tires to slip? and yes, I always pull the fiver with max pressure (80 psi) in the rear tires.
Beaker
Explorer
Apr 25, 2014
But according to some the pin weight will vary from 500 lbs to 1500 lbs depending on where the hitch is mounted on the truck. The pin weight is fixed and can not change.

One more try.

Actually, pin weight can be changed.

Raise the hitch 5ft and see what happens to pin weight? The old lever and fulcrum will apply and pin weight will be less. This of course does not happen in real life, but it means a raiseing or lowering of 1" or 2" for the hitch does mean a change of pin weight but not enough to mean anything.
ependydad
Explorer
Apr 25, 2014
RCMAN46 wrote:

one more try.

Take a hypothetical truck that has 2000 lbs on each axle with a wheel base of 10 ft and without a 5th wheel trailer.

Take a 5th wheel that has a pin weight of 1000 lbs.

Mount the hitch directly over the rear axle. Now you will have 3000 lbs on the rear axle and 2000 lbs on the front axle with a total truck weight of 5000 lbs with trailer hitched.

Now move the hitch halfway between the truck axles. Now you will have 2500 lbs on each truck axle and 5000 lbs total truck weight.

Now move the hitch 5 feet behind the rear axle. Now the rear axle will have 3500bs and the front axle will have 1500 lbs and still have a total truck weight of 5000 lbs.

In all three cases the pin weight is 1000 lbs.

But according to some the pin weight will vary from 500 lbs to 1500 lbs depending on where the hitch is mounted on the truck. The pin weight is fixed and can not change.

When the trailer is hitched to the truck the total truck weight can not change by moving the location of the hitch.

It is simple the true pin weight is the total weight of the truck when hitched minus the total truck weight before it is hitched.

In the real world not all 5th wheel hitches are mounted over the centerline of the rear axle. Some with long boxes may be mounted in front of the rear axle and some that have a very short box may be behind the rear axle.

That clears it up for me. I completely see what you're saying. Looks like I'll be making a code change to my calculators.
Beaker
Explorer
Apr 25, 2014
That's pretty much the crux of my question- does lightening (or loading in your case) of the front axle count towards pin weight?

I don't understand why everyone keeps worrying about axle weights when trying to figure pin weight. The weight of the truck is same with or without the fifth hitched to it. The only difference with the fifth hooked is the weight exerted by the fifth. THE WEIGHT OF THE TRUCK HAS NOT CHANGED.

Moving the hitch forward of the axle orck of the axle may change the pin weight but it will not change the weight of the truck.

How about we get a scale that does each tire separately? That should start a thread about 1000 pages long to figure out how much a truck weighs.

If one is concerned about overloading axles that is another story but the physical weight of the truck does not change by adding or subtracting loads to it.

Forum Discussion

determining pin weight

43 Replies

About Fifth Wheel Group

Related Content

7 pin plug amperage rating?

Dry tongue weight versus fully loaded

Pin Weight

Pin Weight

King pin weight