Chassis construction, more questions...

[cracker39]

Regarding building the chassis for my Squidget, as I mentioned before, a son-in-law is a welder and I am thinking about building my own 5'x9' chassis...that is, my design with my son-in-law doing the welding. But, one of my concerns is placement of the axle for proper balance. I have a local trailer builder that I plan on talking to for advice, but maybe some of you have some expertise in this area.

Here is my current ideas as to the solution to this problem. I’m thinking of doing the following: First, put the finished chassis sans axle on 6"-8” high blocks. Then, place all of the trailer building materials on the chassis, trying to distribute them in the approximate locations where they will be installed (plywood floors, sides, top; framing lumber; battery; even the AC unit and a bag of topsoil to represent the filled water tank).

After all is on the chassis, first, I can weigh the trailer at 3 points, each side and tongue so that I’ll get a rough idea of the finished weight. Then, I'll lower the chassis onto a piece of 4" PVC placed side to side under the chassis, just back of center (and hope the PVC isn't crushed). Then, place a scale under the hitch. I will roll the chassis forward or back on the PVC until I have about 100 lbs "tongue weight". Once the tongue weight is at 100 lbs, I’ll mark the center point for the axle where the PVC ends up. Does this sound plausible? Any comments or suggestions on this technique?

This is where I need technical info from professionals or any of you who have done it already. Is 100 lbs tongue weight about right? Or should it be more? (My bass boat is about 250 lbs at the hitch). If it helps, I estimate now that the entire trailer will weigh between 1100 and 1300 lbs. I want the axle positioned far enough back to track well (no side-to-side sway) when being towed. The farther back the axle is, the better it should track, so maybe more than 100 lbs tongue weight would be advisable. I know that when I load the trailer for camping, most of the weight will in the under bed storage compartments over the axle, but some will be in the front closet and galley cabinet, so the tongue weight may increase slightly after loading equipment and supplies. I have a draw hitch that will support up to 300 lbs tongue weight.

I am also thinking of using the torsion axle rather than springs. I want as smooth a ride as possible. Here's why. My AC will be mounted high in the rear of the cabin and no matter how well I brace it, hard jolts might loosen it and cause leaks. I know from posts that some don't think there is much of a difference, but I think the torsion ride will be added insurance against problems.

Dale

[cracker39]

Northern Tool has torsion axel suspension units for 139.99. This doesn't appear to be a whole axle, just the torsion units. It looks like they weld onto the side rails of the chassis. Does anyone know anything about this system?

http://www.northerntool.com/webapp/wcs/ ... te=trailer

They also sell the high speed hub sets for $41.99. That would be about the price as a standard spring axle set.

[angib]

Whohoo! Many questions!

Firstly for Dale or anyone new to T&TTT, you can see the problem that long URLs (web addresses) give and it's the same as photos more than 800 pixels wide give - which is the text disappears off the right edge of the screen.

To avoid this, either:
- use the URL text facility (hover your mouse pointer over the 'URL' button when writing a message and it'll show you how to replace the URL with text); or
- paste the URL you want into a URL-shortener like TinyURL and then post the short URL here.

Secondly, your target for tongue weight is more like 10-15% of the trailer weight, so unless your tow vehicle needs a lighter tongue weight, you should be looking around the 150lb mark.

Thirdly, your trailer test-balance method sounds very good - you should be able to get the balance exactly as you want it. I bet the PVC pipe would crush, but a bit of scaffolding pole wouldn't.

Fourthly, those Northern Tool independent torsion units are what is mostly used over here. You don't really want to weld them in place - cut pieces of plate the same size and thickness (1/8" or 3/16") as the base of the torsion unit and bolt them together. Now align the torsion units on the chassis and tack weld the plates. Unbolt the torsion units and fully weld the plates. This will not only avoiding 'cooking' the rubber in the unit but will also make the torsion units removeable if needed.

Andrew

[An Ol Timer]

A spreadsheet very similar to one used to do a weight and balance check for an aircraft would work well and be very easy to use. Start with the original trailer and the weights at the 3 main points like with a tri geared plane. You could then weigh each component separately. Then it would just be a matter of shifting the weights and the axle around and letting the spreadsheet do all the work.

[cracker39]

Thanks for the replies. First, I haven't gotten the hang of using the tools on this site to put images in the message, or dropping in html code, even though I am familiar with html as I use it to code my web pages. That tinyurl link sure is great though.

Second even though I use Excel a lot, I don't have the spreadsheets to do the weights and balances you both mention. The calculation of having tongue weight 10%-15% of the gross weight helps to know what to look for in tongue weight after I have weighed the trailer.

Third, Andrew, thanks for the insight on how to mount those torsion unts. You probably saveed me from ruining them with too much heat. Now that I know how to mount them, I think I will use them. That will give me torsion suspension for the cost of a regular spring axle assembly. Darn, now I have to modify all of my graphics to show torsion suspension...

I just keep on learning new tricks fron you guys (and gals).

Dale

[asianflava]

A spreadsheet very similar to one used to do a weight and balance check for an aircraft would work well and be very easy to use.

There is Andrew's weight and balance spreadsheet
http://www.angib.pwp.blueyonder.co.uk/teardrop/tear81.htm

[An Ol Timer]

It is a good starting point, but if you leave it at that, then by the time that you put in all the goodies that they are stuffing in these days, you may end up with an end product that is nowhere near what you started with. Everything added to a tear over a period of time is going to shift the weights and balances around. That is why in an aircraft each time you put anything in new you do a new W&B. I know that if you reach a general starting point with your tear that you can pretty much shift things around as you load up for a weekend and there fore it isn't that critical. In fact I built on the standard HF-1154 trailer with nothing other than cutting off the extra wheels for standing it up on end. I didn't modify another thing and by downloading and using the spreadsheet mentioned I find that I am well within all specs that have been mentioned in any previous posts.

[asianflava]

Honestly, I didn't use the spreadsheet because I had no idea what to input. I don't know what the weights of an unbuilt trailer would be.

[angib]

Honestly, I didn't use the spreadsheet because I had no idea what to input. I don't know what the weights of an unbuilt trailer would be.

That's No 17 on my to-do list. I've worked out weights for different wall and roof constructions, but now I need to automate their use. However this was No 16 until last week but now there's water coming through my workshop roof, so that's jumped straight in at No 1.

Listen in same time next week for the new chart.....

Andrew

[ellisdee9091]

A good rule of thumb for axle placement is 2/3 of the way back from the front of the cabin....a 9' trailer would then have the axle located 36" from the back of the trailer.
steve

[cracker39]

that's a good rule of thumb, but you have to consider how the load is distributed. Lots of weight in the back would lighten the tongue too much. All in the front would make it heavier. Weighing before placig the axle is what I intend to do. That should work if I make sure I have all of the parts and materials on the frame in the right places. Loading supplies and equipment later has to be estimated now. Unles that is you want to go piling all of your supplies on the chassis now...LOL. But, you'd forget something anyway.