Question about my open trailer (physics)
 

I have an 18' open trailer that I purchased earlier this year. Over the summer, I put the trailer together the way I wanted it (relocated d-rings, rewired, put new steck deck plating in the middle). I took my car down to Mid Ohio last month for a DE & couldn't go over 50-55mph or the trailer/car set up a wild gyration where the trailer would start to swing back and forth very badly. I haul with a 1/2 ton Yukon XL with a heavy duty towing package. I am wondering if anyone else has experienced this. Several people have suggested that since the TT is rear weight biased that I should back the car onto the trailer. This isn't an option as the trailer fenders won't allow this.
I'm wondering what is actually causing this & whether adding a sway bar or weight distribution hitch. I'm thinking that moving the weight forward of the trailer wheels will eliminate some of the problem.
I would appreciate any feedback.

How much tongue weight do you have when the car is loaded and lashed, and tools in place?

I am guessing 400 or so pounds is what you want. (Check the rating on your tow pkg- it will spec max trailer weight AND tongue weight).

I would also guess that trailer wheel alignment is critical- not sure how to have that checked though... my guess is the old fashioned way, with a chalkline on the wheel, direct measurements, etc.

Electric brakes, right? What kind of controller- just curious. I use a tekonsha with the accelerometer in it... amazing piece of work.

A

You are experiencing classic trailer sway. Trailer sway is not something to be taken lightly. It can quickly get out of hand and cause you to lose control, even at 50 MPH. I've seen it. In a matter of about 5 seconds I watched a guy towing a poorly loaded trailer full of stumps go from cruising along at ~55, to swaying, to flipping down an embankment. Since that time I have followed the 'rules of the road' to the letter when it comes to towing.

Ideally you want about 10% of the total weight of the trailer to be on the tongue. My guess is that you have 2% or less (maybe even negative). Simple test - load the trailer like you normally would, unhook the latch that holds it on the hitch ball, and try to lift the trailer tongue. If you can lift it off the ball at all, you don't have near enough tongue weight.

While mechanical devices can somewhat mitigate sway, they are intended to deal with things like gusting winds and passing trucks, not an inherent flaw in the weight distribution. Move as much weight forward as you can. If that isn't enough, get a new trailer that allows you to load the car properly. Seriously. Don't f^&* with the laws of physics!

+1 to what was said above. That looks like a steel trailer, so it probably weighs about 2000 lbs. Add the weight of your car and tools, and you are probably at about 5700 lbs. You'll want about 10% of that as tongue weight.

There is a device that you can buy that allows you to measure tongue weight. I have one, but I am out of the country so I can't look at it to tell you the brand. It is similar to, but I'm not positive it is exactly this one:

http://www.sherline.com/lmbook.htm

(No affiliation!) The article should be very helpful to you. As I recall, it cost about $150. There are ways to measure the weight using levers and a bathroom scale if you google around. The lever is needed because the bathroom scale only goes to 250 lbs or so.

You drive the car onto the trailer on level ground, then unhook the trailer from the vehicle and put the device on a jack into the ball receiver. Jack the nose wheel off the ground, until the hitch height is the same as it was when the trailer was hooked to the vehicle. Then read the tongue weight on the gauge. Gently roll the car forward or back using chocks, or better the tie-down straps to prevent a disaster, until the tongue weight is where you want it. Permanently install some sort of stop on the trailer to mark the point, and you can hit it every time.

I have a Trailex, which has a movable stop built in. The whole procedure takes only about 20 minutes. After you've done it, go out and drive the car at 50 mph and wiggle the steering wheel. You will feel the trailer back there - that is unavoidable - but it should feel stable.

Jon

you need more tongue weight, put tools or spare tire on the front, and put some tools and heavy objects in the box

Classic Fu long Oscillation. Rear weight biases on the trailer is making your trailer act like a pendulum. The short answer is you need more weight toward your tow hitch. Just add some weight to the front of the trailer and you should be fine.

agreed. On the Porsche loaded nose first, it's hard to get it far enough forward on the trailer to get the correect weight bias. You might end up making one of your trailer fenders removable to be able to back the car on, or a trailer place can also move the trailer axles back to help offset the load. All in all, you need to get it fixed before you attempt to tow with it again.

Jsutin

I load mine nose first. The Trailex has several mounting points for the wheels, and when I bought it the wheels were placed for a tail-heavy 911.

Jon

I would do this--- try trailer empty on the road-see if problem is present then.
Load car only on trailer -- road test again.
Getting draw bar weight down in all varients of load & unload will give the information a better basis to diagnose.
There is not a big a difference in front to rear weight bias(of the car) as many think(look at corner weights) and a few tools and a box ,-plus the distortion from the axle position -- 3/4 the way down the trailer, and it is easy for the rear wheels to be taking no weight and the trailer running on front wheels only .

hilarious Wow i had no clue their was so much to trailering !

A few weeks ago i trailered my 911 to LA for a race....my father lend me his King Ranch F250... it was my first time towing(long distance), and i did not feel a thing like what you guys are talking about :eek: And I rented a trailer from U-haul.

My very fist time towing was with a GMC 1500 with tow package...oh man that was HORRIBLE. Come to think of it, samething happend as what you are discribing. My suggestion would be to probably upgrade to heavy duty truck to tow. With the GMC i dont think i could go faster than 25 mph before it started to feel unsafe.

With the King Ranch F250, i was snoozing away and i woke up at around 3 am and i saw my brother doing 80 ! i had to slap him silly and tell him its my car he has back there hilarious But in all honestly, if you can get a big truck like the diesel i was driving, it will make a world of difference.

You can buy a Sherline tongue scale http://www.sherline.com/lm.htm to help you setup the tongue weight. I found that on my enclosed trailer the 996TT must be pulled forward a LOT more than you'd expect. I ended up needing about 1200# weight on the tongue in my enclosed rig, which weighs in at about 9200# fully loaded with about 20 gallons fuel in cans, tool box loaded up with all tools, extra fluids for tranny/oil, brake stuff, extra rotors, workbench, jack, stands, airtank... other misc. crap we think we need at the track!

But yea, the trick is to get it all balanced. You'll want some paint marking the exact spot once you find the sweet spot for your front tires to sit. Here's another tip... you might find that you need to remove that box off the front of the trailer, as you might just need to find that sweet spot puts the nose of the car right up against it! :eek:

Mike

If you do decide you need to get the car on the trailer backwards (avoiding the fenders) perhaps you could fabricate some wooden chocks/ramps in line with the fenders that would raise the rear of the car as you reversed over them, then drop down to normal level? Chocks could be removed for transit or left if secured?

Jim

Next time, take a picture of the trailer fully loaded. The rear of the 911 needs to me over the tires. If you need to add toung weight, put some stuff in the front trunk of the porsche.

a bigger tow vehicle wont change much if the geometry n balance of the trailer is off

think seesaw you want a bit more tongue weight so the trailer doesn't bounce on the hitch over tiny bumps

An unbalanced trailer is and going slow is a get you home remedy--not a starting point one. A trailer will take control of a tow vehicle easily enough if it not right -potential write off of race car,trailer,tow vehicle and maybe the occupants .