Building 2-car trailer

[racer-025]

I've started building a 2-car trailer for two ITA CRX's. The trailers specs are:
- 24.0' X 6.5' deck
- tandum 3500# axles with brakes on both
- leaf spring over axle suspension
- 15" wheels with load C rated tires
- 2x4 box frame (2 on each side for car wheels)
- 2x2 cross bracing
- 1/8" plate on wheel tracks only
- tongue 2x5
- 2-5/16" 10,000# ball
- load distribution hitch
- break away kit & brake controller

I'll fill you guys in on the details, and how it hauls if your interested.

[BMW RACER]

I'd think about going to triple axles. A little more reserve load capacity. Have you looked into those torsion axles? I have them on my TPD. They seem to work fine and look a lot easier to mount.
Keep us posted.

[racer-025]

I already have the two 3500# axle assemblies. I think the total gross weight is around 6000 pounds so I think it should be OK. I'm not sure on the C rated tires. May have to go to D or E but time will tell.

[wally]

If you are building a steel 2 car trailer, I would recommend (2) 5200 axles. By the time you figure in the weigth of the trailer, you are close to the capacity of the axles. Bigger axles means bigger brakes, bearings and tires. http://Forum.ImprovedTouring.com/it/smile.gif

Wally
Trailer World Inc.

[apr67]

Get two big axles. Go with oil bath bearings, and brakes on both of them. Torflex are the only way to go.

[JohnRW]

You need bigger axles. My 18' steel open deck trailer is over 1800lbs. all by itself. You need a lot of steel to keep the side rails of a 24' from flexing and cracking.

What is your weight budget for the trailer alone ?

[MMiskoe]

Why box tubing as apposed to C-channel? Channel has a better strength to weight ratio than tube. Compare the "I" and pounds/foot numbers in the steel books. Cheaper too.

It may not be an issue, but box tubing needs its ends capped to keep road salt out, channel has no internal surfaces to worry about.

Paint, paint, paint. Send it out for sandblast prior to wiring & axles. Call up a real paint distributor for their recommendation on primer & top coat. Do it right, do it once. Just did mine w/ a Sherwin Williams epoxy eurothane - looks great & very tough.

Measure your door bottom heights, try to make sure they will clear the fenders when the car is on the deck.

[racer-025]

Weight of trailer estimated at ~1800. 2 crxs at ~2000 = ~5800. So I'm hoping to keep it under ~6200 GVW. I'd like to build it with Torflex but I already have the 2 axles. Worst case I add another similiar axle if it gets over loaded.

I built another trailer (single car - no suspension) using channel, but had undesirable results. The channel kept cracking. This time I figure 4-2x4 box "should" do it.

MMiskoe,

I don't really want to paint this trailer. I am planning on having it hot dipped galvanized.

I put a PDF drawing on my website. Check it out and let me know what you think....
(don't all download at once, lol, it is on geocities w/ not much bandwidth)

www.geocities.com/mcnuttracing/bamtrailer.pdf (http://www.geocities.com/mcnuttracing/bamtrailer.pdf)

[chuck baader]

Nice drawing. Comment: personally, I would move wheels back about 18" leaving enough room to open door on rear car. Serves two purposes...makes trailer more stable pulling, and keeps more weight between the wheels and tow vehicle--less cantilevered load on the rear of the trailer.

I assume you will be using a class 3 load equalizing hitch with torsion bars? Very strongly recommended. Good luck, CB

[MMiskoe]

I didn't mention galvi because of the cost. It is by far the best way to coat something that will be outside. I've seen other trailers done that way.

Cracking of the C-channel is odd. Seems to me it would only do that if it was being flexed repeatedly, especially outside its elastic range. If the sections of tube you've selected are too small, they will do the same thing. What were you thinking for wall thickness?

[BMW RACER]

Are you going to carry your cars like in your plan? How about putting them nose to nose? That way the weight is more towards the axles. You might be able to make the trailer shorter, remember all you need is enough length for the wheels, I used to tow my 2002 on a 10' long trailer.
Keep us posted.

[racer-025]

Chuck,

I'm not sure on moving the wheels back any further, because of the long span between the hitch and the wheels. Wouldnt that put too much weight on the hitch?

My 2500 van has a class III while my motorhome has a class IV. I do have a 10,000# weight dist hitch that I can use on both.

MMiskoe,

I think the C channels cracked because of no suspension X trailer running empty many times X rough roads. I do have a backup plan if there are too many stresses on the frame.

BMW,

I've considered nose to nose, and that may be the wiser idea, especially with my van. I think they could go either way using the motorhome. I wanted to keep the deck at 24' in case I change to a longer race car. I've been racing the CRX for many years now, but the Integra is longer.

BTW, I have 2 identical CRX's as shown.

[chuck baader]

025..If you have the 1000#+ torsion bars for the hitch, you are far better putting the most weight you can between the car and trailer wheels. Look at a commercial truck and where the rear trailer wheels are in relation to the load. Good luck, Chuck

[irondragon]

I think that two 3500pd axles will not provide sufficient capacity. Better to get get a pair of 5K pd axles. The tri axle arrangement will cause tire scrubbing, difficult manouevering and 50% more maintenance.
Also, the 2x4 tube sections seem too light. Please consider using 2x6 unless you plan to use a built up deck edge or rail to add section.
Don't know if you've had experience w/ hot dip galvanizing but you will have to put a 1/4" diameter vent hole in every closed piece of tube. Tiny amounts of moisture or even moist air will cause explosions when hot dipped. I have seen molten zinc blown onto the roof sixty feet above the dip tank.
Matt Miskoe is correct that C sections offer better I per pd but the assymetric section can cause weird flexures at the flange edges.
Best Regards - Bill Miskoe

[wally]

Here's some pictures of a 2 car trailer.

Wally
Trailerworld.com

http://www1.trailerworld.com/Content.aspx?...eContentId=1425 (http://www1.trailerworld.com/Content.aspx?PageContentId=1425)

[wally]

BTW that trailer tip's the scale at 2070. lbs!

Wally
Trailer World Inc.

[alfa]

So what's that trailer go for, wally?

[wally]

The 30' 2 car track model sold for $8900. The owner hauls two Civic SI's for Solo II racing. The trailer with the two Porsche sold for 14K, it was loaded with a lot of options.

Wally
Trailer World Inc.

[irondragon]

I ran some numbers on the 2x4x1/4 tubing. Statically you are OK. Max fibre stress at about 17ksi. Yield probably at 45 ksi.
However this doesn't look at dynamic loads which are hard to determine being dependent on things such as % unsprung weight (low in your case) and spring damping rates.
But I think you will experience gradual yielding over time with these sections, particularly if the suspension ever bottoms.

If you were to use 2x6x3/16 tube you would increase stiffness by a factor of 2.4 and weight would go up 6%
2x6 - I=11.1 W= 9.42 pd/ft
2x4 - I= 4.69 W= 8.81 pd/ft
Best Regards Bill Miskoe

[chuck baader]

025..I'm with Bill -- use the larger section. You (per my rough estimate) are over 2000# just for steel for your trailer. I will be very surprised if your road weight is under 6000#. You also need to look at higher load range tires than standard automotive...i.e., real truck tires. The axles should be fine, but I would seriously consider a third. When engineering a structure such as this, I always used a 50% safety factor. Haven't look at the stresses involved with the static loading of your bridge, but with dynamic loading I would look hard at a greater safety factor. This should muddy the water somewhat. Have fun, Chuck

[irondragon]

- 025
More free advice - and possibly worth what you're paying for it.
Tires: Consider running ST rated tires (Trailer Service). They are designed to run at 50 psi and will carry about 20% more load than the same size auto tire. I don't know what the cost premium is but they save a lot of tire changing agony.
Sooner or later you'll have to stop reading all this stuff and actually cut metal.
Bill Miskoe

[irondragon]

-025
Correction on increase in stiffness by using 2x6 tubing.
I should have compared the Section Modulus numbers, not the I values.
Stiffness increase is 60%. Weight increase still is 6%.
Best Regards - Bill Miskoe

[racer-025]

Thats one VERY nice 2-car trailer! Wish I could afford that one. I'd probably go inclosed though....

When I started this tread, my trailer was already 75% finished. Good, bad or ugly - it is now finished. I did notice that it is perfectly balanced. Maybe thats not a good thing as empty vertually no weight on the hitch. I havn't had a chance to load it up and test it yet. It does have "trailer" tires, C-rated. I'm going to try to get the front car as much forward as possible to get as much weight on the hitch as possible.

Chuck, its only going to carry 4000lbs so I think it will be OK. If not, I'll take your advice and add a 3rd axle out the back and/or bridge the outside members and stiffen it up.

Bill, thanks for the engineering math. I'll load her up this week and take it for a test drive.....

[racer-025]

She's all loaded and were heading to the Targa Newfoundland Rally.

www.targanewfoundland.com (http://www.targanewfoundland.com)

I'll let you guys know how we make out in 12 days....

BTW, I did modify the hitch on the motorhome. It had frame extensions and I beefed the hitch up by welding a 2x2 across the frame and then another 2x2 welded to the hitch and used angles to tie the frame extensions to the 2x2.

I'm glad the gas tank has no leaks....

[racer-025]

I'm back. We just did the 1600 mile trek. The trailer had no problems. It actually hauled quite well without any swaying. I didn't need the load dis hitch because the trailer was perfectly balanced - probably not a good thing. We loaded both cars facing forward and as far forward as possible, putting some weight on the hitch. It did have some flexing of the frame when going over rough roads, mainly under the rear car. The springs did absorbe most of the bouncing. The axles and tires were plently tuff enough to handle the job.

Some things I will change:

I will move the axles back probably 18-24 inches to get more load on the hitch and to help stop the flexing in the rear.

I will bridge the outer frame rails to help stop the flexing.

ps.... We did right-off one of the CRX's. End-for-end rollover down a 12' bank. No one got hurt. After the crew got out of the car, a big-dollar Mustang landed on top of the CRX. Anyone have a spare CRX tub forsale???

picture of red crx upsidedown:
http://www.geocities.com/mcnuttracing/targa.pdf

[This message has been edited by racer-025 (edited September 29, 2004).]

[chuck baader]

A couple of notes....I agree with moving the wheels back..will also make the trailer more stable. As far as adding bridge to the outer frame rails, I would not do that as long as you are getting plastic deformation in the structure. A bridge must flex or it will break. Same with your trailer..let it flex as long as there are no cracks, etc. My trailer is a "flexie-flyer" over many races the last three years with no problems. Good Luck, Chuck

[lateapex911]

So sorry about that....and they called you a "speed bump"!! You gonna take that??!

http://Forum.ImprovedTouring.com/it/wink.gif


------------------
Jake Gulick
CarriageHouse Motorsports
ITA 57 RX-7
New England Region
[email protected]

[racer-025]

That Pacione Mustang crew stole the "H" emblem off the hood of the Honda, glued it to the front of their car and put a slash through it. I'd have to say, our Honda saved their bacon. If it wasn't there, they would have rolled too. They worked all night on that car and it was back in the game by 8:00am the next morning.

Chuck,

There is no cracks within the frame. So you think I should not bother to bridge the outside rails and let it flex? Most of the flex would probably be gone if I move the axles back don't you think?

BTW, that '61 Vette in the picture, broke it's steering shaft and ended up in the woods at 100mph! It too, was fixed up and put back in the game.

[This message has been edited by racer-025 (edited September 30, 2004).]

[chuck baader]

When you move the wheels back you will be making a longer bridge between the car and trailer wheels. At the same time you will have less overhang behind the wheels. I would think that would lessen the movement.

The bridge between the car and wheels will need to be watched simply because it will be a longer span, flex more, and more inclined to break if over flexed.

Were it mine, I would move the wheels then load and find the roughest road around to give it a smoke test close to the welder. CB

[racer-025]

Yes, I definiately want to have it all well tested prior to getting it hot dipped.

Chuck,

After I cut off the spring hangers, what do you think of maybe welding a L angle (2"x 4") on the bottom and outside of the outer frame rails. Then weld the spring hangers back on. Wouldn't that stiffen up the fame enough to still let it flex some, but be stronger for the front car?

[chuck baader]

I assume you mean from the new spirng perch location to the tongue? I see no problem with that, but I would stitch weld it, not solid. CB