Request for feedback on Axle Plan & calculations

[terryjones1]

I am planning on building a "standy", garageable, <16 feet total length.
The body will be <13 feet in length.
In order for trailer to be a "standy", I will need a dropped floor.
The drop floor will be 7".
Ground clearance at dropped floor will be 8".
Other dimensions:
rear to start dropped floor = 72"
drop floor width = 30"
Body length = 152"
Rear to center of axle = 56"

I am ready to purchase my Flexiride axle, hub & drum assembly, electric brake assembly, rims, and tires. Parts list follows:

Flexiride 3500 pound axle
10" x 2.25" electric brake assembly, left & right
5x4.5 hub & drum assembly
14" rims, 5x4.5 - 6" wide
195/75-14 tires

Given:
overhang = 6.25"
hubface = 70.5"
Bracket dimension = 58"
Tire width = 7.68"
Rim width = 6", no offset
Overall body width = 79"
Gives:
bracket to inside tire clearance = 2-3/8"
bracket to outside tire clearance = 10-1/8"
bracket to outside body = 10-1/2"

I would like to request some feedback on my calculation & plans as specified above.

[Steve_Cox]

My garage kept is of similar dimensions as far as the footwell, width, and height. Body length on mine is about 1.5' less. My trailer weighs only 1425#, unless you are building much, much heavier, I was thinking a 3500# torsion axle might give a little bit of a stiff ride. Of course with the details you have planned out, you probably have guesstimated the trailer weight too.

[angib]

Assorted thoughts:

56" to the axle on a 152" body is well back - the sort of placing that would be found on a teardrop. If you have some heavy weights in the back half of the trailer, that would make sense but I'm guessing with a front dropped footwell, that's where you'll have some heavy things, in which case you may get a heavy tongue. No problem if you are towing with a big truck, but it's worth considering.

Isn't 195/75-14 an unusual trailer tyre size? Might it be more sensible to use a 205/75-14 so that replacements are widely available? Admittedly, you might not want the extra 0.3-0.4" width.

I'm with Steve on thinking 3500lb is a bit high even for a 13' body - but then you can order the 3500lb Flexiride rubbered down as low as 2500lb, so no problem.

Minimum overhang is good for axle strength but it means that clearance to the inside of the tyre will be tight. 2-3/8" is plenty to get a wheel box inside face hanging down past the frame (so avoiding rot and rust) but not at the trailing arm, where that inside wheel box face will have to be cut away, which may cause a sealing problem.

3/8" between the outside of the tyre and the outside of the body means that you have to cut away the body side for the full suspension travel, which won't look too good. Maybe some fender flares, or something similar, will be needed.

[terryjones1]

Placement of center of axle:
I will have a D4 AGM battery in the back of the trailer (They are very heavy). I will also have small fresh water & grey water tanks in back. The 60" wide bed will also be in back, along with overhead cabinets. I will also have a spare tire in back. I will have lots of storage space under the rear bed. This is where I will store heavier things.
I will not have propane; nor will I have a tongue box. I will have a small window AC in front.
I will have a Porta Potti in a cabinet at end of dropped floor. (I do not put much flushing water in the Porti Potti.) I will also have a small refrigerator in the cabinet. The cabinet will start at the side of the bed and go all the way to the end of the width of the dropped floor (40").
Starting at the end of the dropped floor, I will have a dinette with storage under the benches. (I expect that I will put lighter items here.) I will have no overhead cabinets in front.
Before I build frame, I will do weight calculations. If I do not get an exceptable answer, I will have to adjust.
Tires:
195/74-14 passenger tires are readily avaible. I found them at the 2 tire stores I visited today. I like the smaller tire width of the 195.
3500 pound axle:
I will have the axle derated to 2500 pounds. I think the trailer might weigh around 1600-1700 pounds. I will probably have 400-500 pounds of stuff that I will carry.
Wheel box & outside body at fender wells:
I will maintain the full 2-3/8" clearance at bracket to tire. The wheel box will be attached to the sub floor in back just behind the drop floor.
It does look like I will cut away some of the body framing at the wheel wells. It will not be much. I plan on having a good sealer on the framing at the wheel well and plywood sub floor.
Thanks for the input.

[Steve_Cox]

Terry,

I did the same thing. Axle placement back like a Tear Drop and the water tank, gray water tank, battery, power converter and other assorted storage under the bed at the back. I ended up with 16% of the weight on the tongue. A little heavy for some, but I prefer it to prevent sway at speed.

[dh]

Terry,

I did the same thing. Axle placement back like a Tear Drop and the water tank, gray water tank, battery, power converter and other assorted storage under the bed at the back. I ended up with 16% of the weight on the tongue. A little heavy for some, but I prefer it to prevent sway at speed.

I'm with Steve on this one, I prefer about a 15% tongue weight.

[Alphacarina]

I will have the axle derated to 2500 pounds. I think the trailer might weigh around 1600-1700 pounds. I will probably have 400-500 pounds of stuff that I will carry

Very good idea - I was about to comment that a lightweight trailer with a 3500 pound flexi axle is going to bounce all over the place. Torsion axles should be rated as near the total weight of the trailer as possible

Don