Axle Help! Calling suspension gurus

[Brettski]

Hello all-

Just about to order my suspension and I want to check my math and make sure I have this right. ANY advice welcome. Here are the facts:

• Going to build the frame 57" wide to accommodate a full size mattress inside.
• Planning on a 3500# axle. This one actually, unless you have a better suggestion.
• I picked that one because I can get it with 6-on-5.5 hubs to match my Toyota 4runner (2015...actually, its "6-139" which I'm 99.8% sure is the same). And has electric brakes mounted already.
• Going to match (eventually) the truck tires (BFG KO2 in 265/70R17 which are 8.8" tread width/10.7 section width).

So how long should my axle be?

I figure like this:
57" frame + 2" clearance (x2 for each side) + 5" to hub?
57 + 4 + 10 = 71"

That last factor, where the tire sits on the hub (centered?) confuses me. HELP!?!?!?

And then, dumb question: anyone using shocks with leaf springs? Necessary? Thoughts?

Thanks all!

 

[IdaSHO]

If I'm reading this right. your overall width is looking much wider than your 4Runner

Consider raising the bed height above the fenders to allow a narrower axle and allow for a "full" mattress.

Under the mattress can be used for cargo/gear stowage. Down low, where it should be.

 

[Brettski]

If I'm reading this right. your overall width is looking much wider than your 4Runner

Consider raising the bed height above the fenders to allow a narrower axle and allow for a "full" mattress.

Under the mattress can be used for cargo/gear stowage. Down low, where it should be.

Well, the edge of the tires/wheelwell will be about even with the end of the mirrors, but the cabin body will be narrower than the body of the 4Runner itself. Thus, even though the wheels are wide, the cabin won't obstruct the rear view through side view mirrors.

 

[Brettski]

You need to know the offset dimension of your desired wheel along with whatever amount of tyre sidewall extends beyond outer edge of wheel.
Arbitrarily creating a dimension from hubface to trailer body bears risk.

Found that the Toyota stock wheel is 17x7 with 15mm offset. And the backspace is 4.5".

The BFG is 10.7" sidewall to sidewall.

Does this mean 4.5" from hubface to back of wheel + 2" clearance + 57" frame + other side = 70" axle?

 

[IdaSHO]

I was concerned more about track width that trailer body width, to make towing easier, regardless of terrain.

Your 57" frame + 4 inches of tire clearance (both sides) + roughly 20 inches of tire (10" both sides) is roughly 81"

Overall width of your 4-runner should be about 75"
And the stock overall track width should be about 65"

 

[Brettski]

I was concerned more about track width that trailer body width, to make towing easier, regardless of terrain.

Your 57" frame + 4 inches of tire clearance (both sides) + roughly 20 inches of tire (10" both sides) is roughly 81"

Overall width of your 4-runner should be about 75"
And the stock overall track width should be about 65"

With 81" width, thats about a 71" track vs 63" on the 4R. I see setups all the time that at 5x8 trailers pulled by Jeeps, Tacos, etc...surely their trailer track is much wider than the tow. Is it a big deal? (I'm genuinely asking- clearly I haven't towed a lot) Thank you.

 

[IdaSHO]

For mostly road going a different track is perfectly fine.

For off road, mud, sand, a similar track width is always better.

For technical off road turns, a narrower track width is arguably better, as the trailer "off-tracking" has less tendency to track wider than the vehicle track width. As in, tight turn around a obstacle doesn't force the trailer to be dragged up and over such obstacle.


Either way, a track width wider than the tow rig is not ideal.

 

[Brettski]

For mostly road going a different track is perfectly fine.

For off road, mud, sand, a similar track width is always better.

For technical off road turns, a narrower track width is arguably better, as the trailer "off-tracking" has less tendency to track wider than the vehicle track width. As in, tight turn around a obstacle doesn't force the trailer to be dragged up and over such obstacle.


Either way, a track width wider than the tow rig is not ideal.

Gotcha. Back to the drawing board on design...temporarily. Steel just unloaded into my garage for weekend fun!

 

[Brettski]

I was concerned more about track width that trailer body width, to make towing easier, regardless of terrain.

Your 57" frame + 4 inches of tire clearance (both sides) + roughly 20 inches of tire (10" both sides) is roughly 81"

Overall width of your 4-runner should be about 75"
And the stock overall track width should be about 65"

Ok. So, let me turn the question around- if I want to match the 4R track of 63", what size axle, hub to hub, to order?

Is the answer 62 hub to hub? If the back space is 4.5 and the tire is about 11" wide, center would be about .5 outbound, so 62"?

 

[IdaSHO]

Your on the right track. No pun intended

Knowing your backspacing and offset is required. As is knowing the exact track width of your tow rig.

Most people seem to error on the narrow side. Then you have the option to run spacers to get it spot on.

 

[HuntfishcampXJRay]

Take a minuite and think about what exactly you are going to use the trailer/camper for? The type of terrain you will be in or on. Will you be setting up camp then going trailing? Are you trail riding into remote spots? Take all of this into consideration before you start your build. That will answer your question on how much width you need. IMO anything from full size to queen size will be hard to scale down to fit perfectly behind your Runner. If you need to go that way think of a maximum width of 4ft wide and going with a RTT. Just my 2 cents. I'm in the process of building one right now. All things considered.

 

[rnArmy]

Read this post and the following post linked below. It will tell you how to determine how wide an axle to get for your trailer:

http://www.jeepforum.com/forum/f27/...d-up-thread-1180456/index29.html#post14977300

When you order an axle, it will have a "hubface to hubface" measurement. The hubface is what is pressed against the inside of your rim. You need to get an axle width that will give you enough space between the inside edge of the tire and outside edge of the trailer frame so they don't make contact when flexing.

The classic WWII military trailers tub width (at the base of the tub) was only 40".

I run shocks on my little trailer; it seems to help. You're better off with a softer spring set-up and a set of proper shocks vs. too stiff a spring.

 

[Brettski]

Thanks everyone.

Took the time to remove both wheels from the 5th Gen 4Runner today and measure hub face to hub face: 64.75"
Maybe that number will be useful for others.

The inside of the wheel had stamped 17x7 1/2J and the number 15. Not sure what the 1/2J means. Does the 15 mean the offset in mm?

Anyway, I'm just going to order a 64" or 65" axle then. Am I correct that the 15 is the offset and if so, then a zero offset wheel would shorten the length of axle needed by that amount (about 1/2" per side = 1")?

Also measured the distance from the inside "bulge" of the sidewall to the other and its about 52"* which would give me almost 1.5" clearance per side on my 49" wide frame. Thoughts?

(*this seems to be different everytime I measure! Not easy to get the tape in the right place. Something between 51.5 and 52.5)