Towing Tilt: Will My Truck and Trailer be BFFs?

[ramnut]

TLDR: Truck is lower than 5th wheel. Bed rail clearance is at 7". Sanity check my numbers please.

This might be a long post, really sorry about that. I really need someone to help check my numbers, because based on all the measuring that I have done at the RV lot, and on my truck, I am showing my truck as being lower than the trailer. Please sanity check me here. I am hoping this can also help others that have a similar setup choose the best setup for their towing situation.

Background / Problem Statement: I have been trying to get close approximations for choosing the right hitch for my new 5th wheel. I just purchased a 2025 RAM 3500 LB DRW, and the Carli 3.25 Pintop w/ Factory Air Ride is getting put on it in 3 weeks. However, before I can take delivery of the trailer, I need to know what hitch combo to have them order to make sure it rides as level as possible. I am leaning towards the Gen Y Executive Gooseneck Hitch.

Trailer:
Brinkley Z3515 (5th Wheel)

Vehicle:
2025 RAM 3500 Laramie DRW w/ Factory Air Suspension

Factory Air Suspension Settings:
Normal Ride Height: Refers to the setting the truck should be in under normal operating conditions. Maintains about +0.5" - 1" of factory rake

ALT Ride Height: Refers to the setting the truck should be in under load/towing operating conditions. Drops the pressure in the air bags to lower the rear about -1" to maintain level ride height with the trailer attached to the truck.

Measurements (STOCK Truck - Normal Ride Height Setting Enabled):
Ground to Top of Bed Rail: 55 3/4"
Ground to Bed Floor: 37 1/4"

Measurements (STOCK Truck - ALT Ride Height Setting Enabled - Approximations since the 1 ton won't drop to full depth not being loaded):
Ground to Top of Bed Rail: 54 3/4"
Ground to Bed Floor: 36 1/4"

Lift Kit:
CJC OffRoad 3.25 Pintop for Factory Air Ride

From CJC OffRoad:


Tires:
Stock Tires: 31.8" Diameter (+0")
Specs

Toyo RT Trail 35x11.5" Tires: 34.5" Diameter (34.5" - 31.8" = 2.7" / 2 = (+1.35")
Toyo RT Trail 37x12.5" Tires: 36.5" Diameter (36.5" - 31.8" = 4.7" / 2 = (+2.35")

From CJC OffRoad:
"Also another factor in this equation is the need to account for tire sidewall compression with the weight of the truck, which takes almost an inch off the tire height."

Rear Lift Height Calculations (Normal Ride Height Enabled):
From Stock -> To Lift Configuration:
2.0" (Lift Kit) + 2.35" (37" Tires) = +4.35"
2.0" (Lift Kit) + 1.35" (35" Tires) = +3.35"

Rear Lift Height Calculations (ALT Trailer Height Setting Enabled):
From Stock -> To Lift Configuration:
2.0" (Lift Kit) + 2.35" (37" Tires) -1.0" (ALT Enabled) = +3.35"
2.0" (Lift Kit) + 1.35" (35" Tires) -1.0" (ALT Enabled) = +2.35"

From CJC OffRoad (verifying logic above with lift and tire height calculations):
"Your math is spot on."

Hitch:
I also have a B&W Gooseneck ball which sits 2.5" higher when seated in the RAM factory puck system. Curt makes a Gooseneck ball which is much lower, which sits 0.75" higher when seated in the RAM factory puck system. (This is a difference of -1.75" of height from the B&W option).



Visual Representation (Forgive my Lack of Drawing Skills):



The RV dealer didn't have a Gen Y Gooseneck Hitch on a Brinkley, but they did have one on a Cyclone. I measured up from the ground to the bottom of the cap on both the Brinkley and Cyclone and the Cyclone was 1" higher than the Brinkley. So I subtracted 1" from the measurements from the ground up to the Gen Y hitch to try and keep everything as close to the Brinkley as possible. That is where the 44.5" came from (measured 45.5 - 1"). However, I found the measurement for the Gen Y Gooseneck Hitch on their website to help give me the distance from the bottom of the pin to the top of the hitch. This allowed me to take the 67" I got from my ground to bottom of Brinkley cap and subtract from that the 21.153" and the 2.000 - 1.750 to estimate the very top of the hitch plate. This gave me a better approximation of 45.65" from ground to bottom of Gen Y hitch pin instead of using the Cyclone measurement of 44.5".

41.6" + Collar = Gooseball height from ground to top of collar

Using these values, this is how it shakes out:

44.5": Use Curt Goose Ball (0.75" Collar) = Truck is lower than trailer by 2.15"
44.5" Use B&W Goose Ball (2.5" Collar) = Truck is lower than trailer by 0.4"

45.65": Use Curt Goose Ball (0.75" Collar) = Truck is lower than trailer by 3.3"
45.65" Use B&W Goose Ball (2.5" Collar) = Truck is lower than trailer by 1.55"

Bed Rails:
Truck: 60.1" (Ground to Top of Bed Rails) - 67" (Ground to Bottom of Front Cap) = 7" of Bed Rail Clearance

Conclusion: It appears to me that I can safely tell the RV dealer to go ahead with the Gen Y Gooseneck Hitch, and that the trailer should be level, while also maintaining a safe bed rail clearance. However, I just want someone who is more experienced to take a look and make sure I am not totally missing something here. These calculations are for a Normal Ride Height Air Suspension setting enabled, which will make my truck even lower if ALT Trailer Height is selected instead.

Thanks for getting to the end of this post

 

[mkmsr]

I would love to help, but half way through this seemed like an old homework assignment that I didn't do. Lol

 

[ramnut]

I would love to help, but half way through this seemed like an old homework assignment that I didn't do. Lol

It's definately going to be a nerd out session for sure.

 

[Dodgeman]

Boy, that is the story problem from hell. I’d sooner figure out the one about a train leaving New York at 45 mph at 1:30 PM.

I have a basic question. Why in the world are you putting a lift kit and oversize tires on a long bed dually truck? Do you plan to off-road with this thing?

 

[ramnut]

Boy, that is the story problem from hell. I’d sooner figure out the one about a train leaving New York at 45 mph at 1:30 PM.

I have a basic question. Why in the world are you putting a lift kit and oversize tires on a long bed dually truck? Do you plan to off-road with this thing?

lol this was my day today.

In regards to the question it is mostly looks and better ride. I will be daily driving it the majority of the time, and only towing heavy initially 2-3 times a year. This will become more frequent over the next few years. I do go off road occasionally (hunting, fishing, etc..), but nothing major. We really liked a trailer that should be pulled by a dually, but not really a fan of how they look stock. So saw some CJC pictures, and decided to go for it as long as the trailer wasn’t going to be too nose high. So… hence the story problem. I know it will lose some of its stock strengths, but Carli has a good lift, and minimizes some of those compromises. Worse case I’ll just throw 35s on it if the 37s are too extreme.

 

[Dodgeman]

Sounds good. We pull an 18,0000 lb 5ver and the dually feels real solid. You won’t regret that choice.

Forgive me for not being willing to check your math. I went through a similar process last year changing to a Curt Flexair pinbox, trying to figure out the impact on bed rail clearance and overall height. I have a CAD program so I was able to make scaled drawings of the old and new setup for confirmation. A bit of overkill perhaps, but in the end I was sure and it’s sort of fun when it’s your own rig.

I think the Gen-y gooseball is a great pinbox. It’s the way i’d have gone if I hadn’t needed a slider with the short bed.

 

[CdnHO]

Sometimes you have to make a choice. Do the job or how it looks?