Trailer weight distribution?: Off-topic discussion forum: Grassroots Motorsports Magazine

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Oct. 27, 2009 3:08 p.m. 914Driver SuperDork

I'm building a trailer for the Cortina and I see by some recent posts trailers that either in reality or by photographic optical ollusion, it appears the axle is far aft of the center of balance.

Without a car built and without the computer prowess to formulate an answer via modeling; is there a ball park location for the axles? I know you want 10% of the gross weight on the ball, but is there a way I can make a trailer without knowing exactly the CG of the vehicle?

I can eyeball the vehicle and guess that the weight will be somewhere between the firewall and the driver seat; where should that be on the trailer?

Too much forward weight scares me, too much aft scares me worse, what to do? Knowing the car is nose heavy, 50/50 axle location works, my friend says no. more aft.

Thanks.
Oct. 27, 2009 3:42 p.m. oldopelguy Dork

10% is easy math, make it 11' with 5' behind and 6' in front of the axle. Better still I use pretty exclusively that 5-5.5" of every foot is behind the axle. Easier to build it longer than necessary in front and slide the car back, not so easy to slide it out over the tongue if you err the other way. Too much tongue weight can be made up for with a weight-distributing hitch, not much you can do about too little.

That said, conventional wisdom is 10% tongue weight, but that's more for double-axle trailers. On single axle trailers I way prefer 12-20. Double axle trailers tolerate less tongue weight without getting tail happy, and tail happy is bad. For a car under 2500# there's always some debate about a sturdy but light single axle trailer vs the big double-axle trailers to haul it and I've been on both sides of that fence.
Oct. 27, 2009 4:11 p.m. sachilles Reader

as long as you make the bed big enough, you'll be able to move the car back and forth to get it right. The side benefit is that by giving it a better range of weights you'll be able to accommodate a wider range of cars.
Oct. 27, 2009 4:12 p.m. foxtrapper SuperDork

The 10% tongue weight notion was created for people who can't think. It's a guideline to help keep morons from being any more unsafe with a trailer than they are already.

Far more important is to load the weight around the axle(s), and as close to the axles as possible.

Lots of car haulers cannot do this because the trailer will extend so far behind the axle that it drags on the ground everywhere. So, either the trailer goes up, or more frequently the axle goes back.

Do not get into the silly massive overloading of trailer tongues that some folks get into. They seem to think that if 10% is good, 20% must be better. It isn't. That tends to overload the tow vehicles rear tires, unload the tow vehicles front tires, overload the trailer hitch. When you're towing, your rig and trailer should not be looking like a broken back pickup truck.
Oct. 27, 2009 4:26 p.m. andrave HalfDork

You should probably buy some preengineered trailer plans or buy one of the many good books that have been written on the subject. Or just find a trailer you like outside tractor supply and measure everything with a tape measure.
Oct. 27, 2009 6:19 p.m. iceracer HalfDork

On my double axle trailer,carrying a ZX2. The ZX2 has app.62% on the front wheels. So I figured where the CG would be and located it just a little ahead of the center of the two axles. Needless to say the car was quite far back but it towed very nice.
Oct. 27, 2009 6:37 p.m. Toyman01 HalfDork

Set the axles just behind center of the deck. The last one I built was a eight foot trailer and I set the axle back about 6 inches. A tongue heavy trailer is easier to load than a balanced one. If you aren't sure, build the axles on a sliding carriage. That way as cars come and go you can adjust the trailer to fit the car.

As far as loading I take a guess and adjust as necessary.
Oct. 27, 2009 7:17 p.m. blaze86vic Reader

One tip in making your trailer. My trailer has a unique characteristic that I haven't seen in other car trailers. I have a 2 axle setup, and when the trailer is completely empty (no tires on it), it balances freely on the front of the two axles. This makes it incredibly easy to maneuver it by hand into it's storage spot between the house and the fence. And it also means that I can pull it out and mow under it without hooking a car up to it. Very handy feature.
Oct. 27, 2009 7:18 p.m. blizazer New Reader

Id think that turning the entire rig comes in there somewhere too. If you center the axles, the back of the trailer will be swinging out into mailboxes, gas pumps, parked cars, etc.
Oct. 28, 2009 6:07 a.m. 914Driver SuperDork

I had a 19 ft. two axle before; in an effort to save weight this one is 6 X 10 single axle, not much bigger than the car. That's why axle location is critical, I can't move the car fore & aft.

Dan
Oct. 28, 2009 8:24 a.m. Dr. Hess SuperDork

Dan, if you're going to make it that tight and single use, you're going to have to know what the weights are on your car.
Oct. 28, 2009 8:49 a.m. 914Driver SuperDork

You're right.

Lets try this: With the trailer complete except for axle welding, put the trailer up on two 2X4s at each corner. Put the car on the trailer. With a scale on the tongue, lift gently with a floor jack under the suspected axle location. Move the axle fore & aft to get ~10% of total weight on the scale.

Whaddaya think?
Oct. 28, 2009 9:48 a.m. andrave HalfDork

If you make the axle a sliding axle, you can slide it all the way forward and make the rear a beavertail and you won't even need to use ramps.

its trick.