Location of torsion axle

[Katie&Craig]

I was playing around with Andrew's tongue weight spreadsheet (again) after just ordering a torsion axle. Since the tires will be on the inside of the trailer, it is important to get the location of the axle pretty close to right.

My question is: the measurement for axle placement on the spreadsheet asks for "wheel center from rear". On a regular axle the wheel center is where the axle is. On the torsion axle (ours will be at 22.5 down) the wheel center is in front of the axle by about 6" or so. So when figuring out axle placement for a torsion axle, is it still based on where the axle is, regardless of the wheel center?? Is there some weird engineering balance thing where the placement would be based on the wheel center and not the axle bar??

I know this is probably obvious, but not to me, so please enlighten me.

Our teardrop body design is 116" long. 42"-44" seems to work per the spreadsheet (at least with the input we have figured out). I didn't think about the wheel center not being the same as the axle in the prelim drawings (hadn't decided on the axle then), so need to get this figured out so we can actually start to build!
Thanks,
Katie

[SteveH]

Katie,

It's always on the wheel center, no matter the axel. That is because the trailer ballances on the wheels, and that is what sets the percentage of gross weight on the tongue.

[angib]

Is there some weird engineering balance thing where the placement would be based on the wheel center and not the axle bar??

Yup, there is indeed a weird engineering balance thing at work here. That's why I used "wheel center" as I hoped that would be clear - hey, I even spelt it 'center', not 'centre', to make it easy! The only thing that matters is where the wheels are.

Of course, when positioning the axle on the trailer, you have to locate it so that the wheel centers, not the axle center, are at the measurement you decided on.

Andrew

[madjack]

On the torsion axle (ours will be at 22.5 down) the wheel center is in front of the axle by about 6" or so.

K&C, are you sure the wheel goes in front of the axle...I do believe you have your axle turned around the wrong way...the torsion arms should be in the "trail" position with the wheels behind the axle...
madjack

[Ken A Hood]

I messed up early on as well. While still new to the whole TD trailers I found a set of 1/2 torsion axles. They're 5 on 4 1/2 spacing 2000 lbs...and they are 22.5 degrees down, I thought that meant a lower ride; but of course the down angle means they ride higher (22.5 degrees below the horizontal plane)

They're still sitting in the garage

[angib]

but of course the down angle means they ride higher (22.5 degrees below the horizontal plane)

They're still sitting in the garage

Do tell. Is the garage now riding higher?

Andrew

[Jiminsav]

ooh ooh ooh..Mister Kotter..
Yes Arnold?

Mister Kottor...the wheel center for a torsion axle is in the center of the wheel, BUTTTTTTT..the center of gravity for the wheel will be a point halfway between the center line of the axle and the center line of the torsion bar.

[BrwBier]

So, what your saying is that if I want my center of gravity at 35" from the rear and my torsion arm was 12" long, then I would put the mounting plate 6" forward of that point. I didn't know that. I'm glad I read this post before mounting my axle.
Thanks
Brwbier

[Katie&Craig]

Wow- I am learning more then I every thought I wanted to know. Thanks Steve & all for clearing this up.

Andrew - I know you have made your spreadsheet clear, but there will always be people like me who overthink things and then just get themselves in a muddle about it. I was fine the 15 or so other times I played around with your spreadsheet.

Madjack - it would be bad news to mount the axle backwards. Luckily I don't have it yet so haven't caused any damage yet. The wheels being further back is actually better. Don't worry too much - Craig told me this afternoon that I had it backwards, so at least one of us is paying attention.

Ken - the ride height should be where we want it. The place we bought our axle from printed out some nice drawings specifying all the measurements, including the ride height at no, half and full load. Half load puts it about perfect for us in terms of our galley plan.

Jiminsav - I'll have to consider that when finalizing our plans.
Katie

[Jiminsav]

Brwbier,
not to add more confusion, but where the mount plate is, isn't what I meant..I meant that, to position the mount plate, put the center of gravity line where you think it should be, then position the mount to put it there..the mount bolt holes may or may not line up with the center line of the torgue tube.