Tail stabilty; Trailers and Trucks

[rmel]

I got a College physics refresher this past week on sympathetic resonance.
That is, if you put weight in the wrong place your trailer can do the driving for you.

I have a Sankey III which I put a fair amount of work into getting bows added for
a roof-rack tent, as well as a swing gate for the spare tire. The later has turned
out to be a very bad mistake I thought I share that here. Looks nice though see PIX.

Basically the weight of the gate + tire is a bit over 100 lbs, all hanging off the rear
of the trailer about 2' above the center of the Axle amd 6" away from the tail gate.

I was driving down a rough patch of HWY 101 near Gilroy and got a very nasty surprise -- the
rear end of the trailer started to bounce around -- up and down, side to side. I was going slow
enough that I recovered pretty quickly. This was pretty early on in my travel to Mojave so I had
to be extremely cautious -- it did happen at least one more time on the return home, again a
patchy section on HWY 5.

The rough patches in the road were sufficient to put ample energy into the system to sustain an
oscillation in spite of the shocks.

I did take special care to make sure the load in the trailer was well balanced, the tent weight is
75% over the axle but the real problem is I had a heavy pendulum in the rear waiting to get "excited",
and is the worst possible place to position this weight for stability. The spare hard mounted near the
yoke would have been far more stable but this would have interfered with the Pinz spare. The yokes
on these Sankey's is EXTREMELY short (avoiding jack knifing is another bit of fun).

The fix is the Tire and Swing out gate are now kaput, removed, gone, forgotten. I'll get a Pinz to
Rover wheel adapter made so I can use the Pinz spare on the trailer if ever needed -- tire takes up
too much space in the trailer floor that's why I wanted to Gate mount spare in the first place

This got me thinking about some Pinz's I have seen with up to 6 Jerry cans on a rear swing out
gate -- when full that's about 180 Lbs of gas alone and although not a trailer and should be more
stable the physics are the same.

IMG_1058 - Version 2.jpg (61.73 KiB) Viewed 4513 times

[David Dunn]

Ron, Ron, Ron.
Always have at least 10% tongue weight! You get less, the trailer will sing and dance around behind your tow vehicle. If the trailer was a car hauler, it would have thrown your Pinz around
Sankeys are well balanced to start with, and you need to watch that you load accordingly .
I have a tongue scale for when I load a vehicle on a trailer for the first time. I've been through Mr Toad's wild ride a couple time. No fun

[rmel]

Ya! I did watch my tongue weight. I actually recall your recent post on the 10% rule.
I don't have a scale so it was totally by the Armstrong method By 10% I have
been assuming 10% of total load on tongue, which would inc. anything added to the
trailer inside as well as bolt-on adders -- assuming an empty trailer has 10% on the tongue by
design. I had a fair amount of weight up front with 2 + 2 Jerry cans Gas + H2O, lots of
fire wood, the tent. although not heavy is shifted forward to put at least 10% of itself
on the tongue. It's possible I didn't have enough weight on the tongue but now with the
Swing gate and tire removed it will be a lot easier to get in the ballpark.

This was a very scary situation even more than getting stuck in the sand in Mojave

[NEWFISHER]

I have always tried to keep the spare mounted under the trailer nust forward of the axle centered. The only one I cant do this on is my lowered car hauler and it sits at the front of the deck on the chin bar.

Spooky ride Im sure, glad you werent swapping paint with the oncommers!

[rmel]

Mounting under the trailer would certainly add a lot of stability but at the cost of trail clearance

I am now sold on the idea of a wheel adapter, and just get double use on my Pinz spare.

[TechMOGogy]

It does look good!
Wheel adapter sounds like a good plan

[David Dunn]

Ron,
I doubt the empty tongue weight of a Sankey is anywhere close to 10%. In MoD storage, trailers are stored with the drawbar on the ground and with them resting on the tailgates (tongue up). Well balanced. With them setting tailgate down, they would self drain. Fairly simple for one person to lift the tongue up. On most of my US trailers, it's tough enough just to slide the drawbar on the front leg, let alone lift them... sort of 2 different mentalities of militaries.. the Brits assume the trailer will be loaded correctly, and the US military figures for the worse and preloads the tongues with the axle a bit further back.

Years ago, I bought a Sherline tongue scale for checking tongue weight when I loaded different vehicles onto trailers (marked the trailer if it was repetitive load)
http://sherline.com/product/sherline-tr ... ght-scale/

There are sites that will show you how to use a bathroom scale to measure tongue weight.

Have you thought of making a tire carrier to the underside of the tent rack? There appears to be enough room and not interfere with getting into the trailer.
Give me a call.

[Jimm391730]

I agree with all that has been said, but think that one of the major culprits was that with all that weight at the furthest rearward point, all counterweight had to go fairly far forward to balance - more like a baton with weighted ends. this would store significant rotational energy, both up and down and side to side. Much different than the same amount concentrated in one point, just forward of the axle (for tongue weight). DD has a good idea, putting the spare under the tent, but always lower is better. Another idea: put it on the tongue, but offset to the drivers side (even extending 6" beyond the side of the trailer) as to not interfere with the Pinz spare. You might even be able to lower it to the level of the bottom of the frame for lower mass but no impact on clearance. The offset weight of the tire should not be significant when loaded.

[rmel]

My very first design had the spare on the tongue side, if it weren't for this VERY short yoke
that would have worked out but unfortunately I would have had interference between the
spare on the Pinz and the spare on the trailer.

I thought about putting the tire under the tent but jumped to the swing gate idea.
I kind'a wanted good reach and clearance to get stuff inside and out of the trailer
from the sides and thought the tire hanging upside down would get in the way. I might
rethink that a bit now.

The rear is just the worst damn possible place to stick this weight for stability. It's a classic
counterweight+spring+dashpot example Arggg....should have known better.

I also liked getting that Trasharoo bag on the spare but what the heck. That's gonna go to
the Pinz spare now.

Hey I even have LED lights, 70W Solar, and a pair of UPS batteries in this trailer -- which all
added up is pretty lite weight in comparison.

[David Dunn]

Weeeell Ron, Tell you what I'll do. Since you can't keep everything you want in the Sankey (and get the TW right ), I'll "let" you trade it back for one of my M116A3's, OR possibly my M101A3 ( a true late A3 with 55" between the wheel wells ). The M101 has a 6x8 bed with sides and canvas. They all have raised axles.
But you'll have to repaint the Sankey to RAL6031

[NEWFISHER]

What about running an extended tongue ( collapsable) and putting it back up front?

[David Dunn]

Jon,
Extending the tongue is not practical. The Sankey Mk3 has hydraulic disc brake with a lunette eye.
Much easier to extend the pintle further out.

Don't bug me now, I'm trying to make Ron feel bad and get back my Sankey
He caught me during a weak moment , and just before I learned of GG. He'd never have gotten it then.

[rmel]

Keep trying Dave. I love this trailer

BTW I did extend the Pintle by 4.5". Modest turns were interfering with the rear bumper tubes.
This extender helped that problem out considerably. Going much beyond this would create
other problems. I now have one heck of a knee knocker that beats the old style Pintle

IMG_0796.jpg (92.8 KiB) Viewed 4403 times

[rmel]

This should also be linked to the Adapter thread. But, I Just got a custom wheel adapter so I can
use my Pinz spare on my Sankey trailer. The trailer uses Rover wheels (Defernder pre-1999) with
a Bolt pattern 5 x 6.5", and the Pinz at 5 x 160mm.

Adapter.jpg (31.21 KiB) Viewed 4205 times

There's a few things to watch out for. First don't assume the hub diameter that the adapter centers
on is standard, mine was not the typical Rover hub. If you have a protruding hub measure it with a good
caliper then add 1mm to 2mm for bore hole clearance. Second, make sure you compensate for the
different tire offsets to ensure wheel wheel clearance, that's why this adapter is so darn thick.

AdapterMounted.jpg (27.22 KiB) Viewed 4205 times

Rover Wheel mounted

RoverWheel.jpg (37.86 KiB) Viewed 4205 times

Pinz 285 16r70 tire mounted

PinzWheel.jpg (26.67 KiB) Viewed 4205 times

As Haf-e has pointed out on the Adapter thread, an excellent choice for custom
adapters and spacers is Motorsport Tech out of NV. Lenny is the owner and great
to work with.

Now no need the tire gate and the instability that presented going down the HWY

[Haf-e]

Looks good - glad that the guys at Motorsports worked out for you.

Did you make the spacer that wide in order to match the track width of the trailer with the Pinz? Looks like the Pinz wheels are further out than the LR wheels? Most trailers are wider than a pinz so that seems backwards - but I guess you have wider wheels also.