Ski Bum Truck V2.0, F450 Rough Road RV

[java]

Coil length is determined by desired ride height, and wheel position at full droop. Find the difference between the full droop position and your desired ride height. Then cacluate the springs compression based on its rate and the spring weight. For the 650lb springs that is about 4". If you have more than 4" of droop from ride height, you need a softer spring, or a droop limiting strap.

For example, you have 16" between the top and bottom spring perch at full droop. You want the ride height to be 4" lower than that . So a 650lb 16" spring does the job. Another option if you can't get the length or rate you want for the ride height, is to compress the spring with a compressor, so that the suspension has a bit of preload in the full droop position.

OK thanks, the OE springs had no preload, IE I could remove them by unbolting the shocks and lifting the frame off the axle. If I wanted 1.5" lift in theory I could measure the OE springs and add 1.5" of height correct? They are stashed in the attic I think.....

I can do full droop and some math too.

Does that bag data mean anything to you?

Thanks for the help!

 

[luthj]

Lengthening the spring would directly increase ride height. In some cases you can install spring spacers top or bottom. I don't know about the F series though.

You should confirm that you aren't hitting the bags internal bumpstop. Easily done by airing the bags down until the suspension doesn't move any more.

That spring is mostly linear (for an air spring). All air springs are progressive, so they increase their spring rate at they compress. If the static height of the spring is too tall, you will have much higher spring rates near the bottom. That spring is designed for 8-9.5" at static ride height. What does your spring measure (between the mounting plates)?

 

[java]

Lengthening the spring would directly increase ride height. In some cases you can install spring spacers top or bottom. I don't know about the F series though.

You should confirm that you aren't hitting the bags internal bumpstop. Easily done by airing the bags down until the suspension doesn't move any more.

That spring is mostly linear (for an air spring). All air springs are progressive, so they increase their spring rate at they compress. If the static height of the spring is too tall, you will have much higher spring rates near the bottom. That spring is designed for 8-9.5" at static ride height. What does your spring measure (between the mounting plates)?

Yes I wanted a 1.5" increase from factory height (bags do that as well)

Not bottoming out. I still had at least 1-1.5" of uptravel from my zip tie to the bottoming out point. I have dumped the air completely, its almost exactly 7/8" of shock shaft left. I am running them at 8" tall. I tired 9" and 9.5" this weekend. I didnt like how the bags sat on the bases, almost trying to "flip" off them.

At 8"

Zero psi in the bags

9"

And here you can kind of see it "flipping" on the mount

 

[luthj]

The other part of the equation is tire pressure. What size and pressure do you run normally?

 

[java]

The other part of the equation is tire pressure. What size and pressure do you run normally?

And another blow.... 285/70r19.5 Soooo a stiff tire. 65psi IIRC is what is in them now. Might be 70

 

[luthj]

A glance at some generic load tables (you should look up your tire), stops at 85 psi (its a DOT thing). extrapolating the average shows you need 59psi to carry 3200lbs per tire. Depending on the tire MFG, that may be very conservative though. Check your MFGs tables and do the math, but you probably are running 10PSI higher than needed.

 

[java]

A glance at some generic load tables (you should look up your tire), stops at 85 psi (its a DOT thing). extrapolating the average shows you need 59psi to carry 3200lbs per tire. Depending on the tire MFG, that may be very conservative though. Check your MFGs tables and do the math, but you probably are running 10PSI higher than needed.

Very possible...

Here is the load table for my tires. Straight from Toyo. Averaging between 80 and 100psi ranges, gives us 54.57lbs/psi. So In theory I need 58psi ish. (3200lbs per side, I added a bit for the new tires, at 55lbs/psi) I guess I can drop and see what tire temps do. I ended up here as they "look" low with much less and the temps were even across the treads.

 

[Buddha.]

Is your passenger side shock leaking?

 

[java]

Is your passenger side shock leaking?

I sure hope not! I sprayed them with anti rust crap. It's a waxing stuff, that's probably what your seeing.

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[Buddha.]

I sure hope not! I sprayed them with anti rust crap. It's a waxing stuff, that's probably what your seeing.

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I didn't see it on the drivers side shock so I wasn't sure.

 

[Alloy]

Frustrated.

Should I go back to coils? Just try to find taller softer ones?! Anyone have an idea of spring rate needed? 6200lbs on the front axle.

With that amount on the front things should move easily. What was (before Kelderman) the front axle weight rating?

Today I was comparing 2018-2019 F450PU and F450/F550 Cab and Chassis rear suspension parts. It is surprising how many parts are the same.

Tomorrow l'll compare the front suspension parts.

 

[Alloy]

Zero psi in the bags

That bag looks like it is out of alignment. Are both sides like that?


Both GXV and Earthromer use King shocks wonder why?

 

[java]

With that amount on the front things should move easily. What was (before Kelderman) the front axle weight rating?

Today I was comparing 2018-2019 F450PU and F450/F550 Cab and Chassis rear suspension parts. It is surprising how many parts are the same.

Tomorrow l'll compare the front suspension parts.

They are all the same other Than the frame itself. This was a PU originally.

Front axle rating is 6500lbs

Yes both sides are angled like that. The drivers side is actually offset a little more.

And on the King vs Fox, IMO they are very comparable. I went fox as the guy I got the best discussion with uses Fox.

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[patoz]

Gabe, are you comparing rear cargo area frame widths between the standard PU trucks, and the commercial cab/chassis trucks? If so, then no they are not the same width.

The standard PU truck frame width is 42" OD, if I remember correctly. I measured my 2004 F250 one day. The 'E Series' is also 42", which I'm positive of (I have one).

The commercial cab/chassis frame width is 34.2" OD. This is a national standard and may even be an international standard. This is so up-fitters, i.e. ambulance, U-Haul, utility vehicle, etc. manufactures can build their bodies and be able to put them on any brand of cab/chassis truck.

Having just built this F350 trailer frame a year or so ago, for my 2005 Wheeled Coach ambulance body, I know for sure exactly how wide it is after the number of times we measured and remeasured it.



I'm attaching a PDF from the Ford Up-fitters Manual that supports this.

 

[java]

@patoz no I said they were the same except the frame! Yes my truck is a PU and has a winder frame. Iirc it's 38 ish. There is also a hump above the axle and iirc it's differnt at the back of the cab also. The cab chassis is flat, pu is not.

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