Do I Understand Weights Correctly

[RoadEyePie]

For Example:

Curb Wt. of truck = 7000
Cargo Wt = 500
Hitch Wt - 2500

GVW = 10000

GCWR = 24500

Therefore I can tow a 14500 lb trailer?

[Tdave]

Originally Posted by manwithnorv

For Example:

Curb Wt. of truck = 7000
Cargo Wt = 500
Hitch Wt - 2500

GVW = 10000

GCWR = 24500

Therefore I can tow a 14500 lb trailer?

Are you stating that the factory pin (hitch) weight limit is rated at 2,500lbs?

If so, then you technically need to weigh the combined rig (truck and trailer) to really know if you are within spec.

Rule of thumb is that pin weight of a fifth wheel is 20% of its curb weight.

So if the GVWR of your 5er is 14,500 (fully loaded), assume pin weight is 2,900lbs.

Thus, you would be overweight at when trailer is fully loaded.

However, pin weight does depend on where the weight is in the trailer. A front mounted generator, for example, really drives up the pin weight. Same with a washer dryer mounted in the front master bedroom closet. Or a front living room, or front kitchen layout.

Opposite happens, too. If your weight is more at the rear of the coach, then pin weight will be less.

That's why weighing on a scale is the only way to really know.

But if you are trying to buy a trailer to match a truck you already have, then err on the side of caution, since you can't weigh before you buy (unless you have a very cooperative dealer). Or you can poll the forums for what weights people have seen with that same model trailer (rv.net 5er forum has a sticky on that topic).

And don't forget that most 5er hitch assemblies add about 200lbs to the rear axle, which also drives up the pin weight...

So, doing that math, if you are limited to 2,500 pin, you'd have about 2,200 free (subtract for hitch and weight load you'd be carrying in truck that would distribute to the rear axle), leaving you with 11,000lbs curb weight ability to tow (assuming 2,200 is 20% of the weight of the trailer).

[Go Dawgs]

Make, model, year of truck with options. Without that no one could tell you the correct answer. After you have that info go to trailer life on-line for towing guides. Look up you specific truck and it will give you guidelines on towing limits. I have also in the past gone to a dealer and given them my vin # and they looked up the specifics of my vehicle.

[RoadEyePie]

I was asking if the simple formula is correct, not about the numbers...I was just picking dummy numbers. Addition, subtraction...that's all I was asking.

Perhaps:

GVW = Curb Wt + Cargo + Hitch Wt.

Max. GTW = GCWR - GVW

?????

[Palmeris]

Originally Posted by manwithnorv

For Example:

Curb Wt. of truck = 7000
Cargo Wt = 500
Hitch Wt - 2500

GVW = 10000

GCWR = 24500

Therefore I can tow a 14500 lb trailer?

check this out, you may find it helpful
RV Tow Check App | Salesperson Fact Checker

[Tdave]

Originally Posted by manwithnorv

I was asking if the simple formula is correct, not about the numbers...I was just picking dummy numbers. Addition, subtraction...that's all I was asking.

Perhaps:

GVW = Curb Wt + Cargo + Hitch Wt.

Max. GTW = GCWR - GVW

?????

Again, your tow weight potential is limited by your rear axle gross weight rating (with a 5er).

Unless you are within spec there, forget everything else.

[RoadEyePie]

Originally Posted by Tdave

Again, your tow weight potential is limited by your rear axle gross weight rating (with a 5er).

Unless you are within spec there, forget everything else.

The manufacturer's GVWR is the maximum weight that the vehicle can sustain, which is based on the axle weight rating, and other etc. etc. etc.

GVWR = Curb Wt. + Payload
Payload = all added weight including hitch weight.
Payload has to take into consideration the vehicle's axle weight capacity.

Therefore, if I don't exceed the GVWR, I shouldn't exceed the axle weight rating.

[Tdave]

Originally Posted by manwithnorv

The manufacturer's GVWR is the maximum weight that the vehicle can sustain, which is based on the axle weight rating, and other etc. etc. etc.

GVWR = Curb Wt. + Payload
Payload = all added weight including hitch weight.
Payload has to take into consideration the vehicle's axle weight capacity.

Therefore, if I don't exceed the GVWR, I shouldn't exceed the axle weight rating.

Not technically correct. Typically, there will be an axle GVWR, and also a pin weight rating.

For example, my truck, a 2004 GMC Sierra 3500 DRW, has a rear axle weight rating of 8,550lbs.

Unloaded (except for passengers, fuel, and light cabin cargo), my rear axle curb weight is 3,620lbs as per a CAT scale.

That would suggest I can support a pin weight of 4,930lbs.

But according to my factory manual, my pin weight (towing) limit is 3,500lbs.

Shear forces are different than compression forces. The trailer pulls on the truck, where a static payload in the bed pushes down (for the most part), which is why the pin weight rating is less than just the difference between axle GWR and curb weight.

[RoadEyePie]

So if the simple equation that I stated is incorrect can you please state the correct equation? I honestly didn't follow your thoughts. I'm trying to find the formula for calculating this based on the data that the manufacturers (of vehicle and trailer) give you.

[archer75]

There are lots of towing calculators online. I'd just google some of those. Ultimately what you can tow is all about payload as you'll max that out long before the tow rating.

[Tdave]

Originally Posted by manwithnorv

So if the simple equation that I stated is incorrect can you please state the correct equation? I honestly didn't follow your thoughts. I'm trying to find the formula for calculating this based on the data that the manufacturers (of vehicle and trailer) give you.

Yeah, sorry if I confused you when I wrote "your tow weight potential is limited by your rear axle gross weight rating (with a 5er)."

What I should have written was "your tow weight potential is limited by your gross pin weight rating (with a 5er)."


Let me ask you this: what are you trying to achieve with this calculation? How heavy of a trailer you can buy and safely tow?

[RoadEyePie]

I'm just asking if the equation is correct or incorrect. I like to understand how to derive these things and understand the relationships. I'm not much one for trusting calculators, website tables. If you don't understand, then you never know if the answer is correct. I do trust the manufacturer's published specs.

[archer75]

Originally Posted by manwithnorv

I'm just asking if the equation is correct or incorrect. I like to understand how to derive these things and understand the relationships. I'm not much one for trusting calculators, website tables. If you don't understand, then you never know if the answer is correct. I do trust the manufacturer's published specs.

It's all about the payload. Start with what is printed on the door sticker. Deduct all the weight including people and cargo in the truck. What is left is what you have available for pin weight. That's what the calculators are doing. They also verify you are within your other limits. But if you are in your payload limit you'll usually be ok with the others.

Usually GVWR - curb weight = payload. However the payload you go by is what is printed on your door sticker. So go check that and you'll know for 100% certain.

In another thread you talked about getting a DRW vehicle and a 35'-38' 5th wheel. I have not yet come across a 5th wheel in that size a DRW couldn't tow. Maybe chevy's(2017's, not sure on the newer ones) as they have lower tow ratings than Ford and Ram. But you'd have to check the numbers.
The fast lane truck has some great youtube reviews of trucks for towing.

[Mich F]

Originally Posted by manwithnorv

Therefore, if I don't exceed the GVWR, I shouldn't exceed the axle weight rating.

Not neceesarily. You could be at or under the GVWR with your front axle under it's rating, but your rear axle is over it's rating.