Car Tie Down

#1

Starting a new post as we are specifically talking about securing the car to the trailer now.

As I have said previously, I don’t think it is a good idea to hook to the lower shock mount of the trailing arm to secure the car. Anything you do to make your car fast will be lost if the alignment gets out of whack. I check my alignment before each event and it needs adjustment about every other race or so. It all depends on how many ¾ of track passes I make (two wheels in dirt over curb). I would like someone who has some toe plates to put their car on the trailer and check the rear toe. Now secure the car for a trip. The front suspension will be compressed but the rear will not so toe should be the same. If it is not, the tie down it putting strain on something. Securing to the rear sub-frame is much better but you are still pulling on something that is held in place by two long bolts through bushings (although the bushings may be solid).

The argument about crossing straps is that if one of the straps fails, the car is pulled to the side and now loose from all straps. If you strap straight back and loose a strap, the other three are still tight. To get any side to side movement the straps would have to stretch more.

BMW designed tie down points in the car. The two front ones are obvious but the rear ones are not as much. If you look behind the rear wheel on the inside of the fender you will see a hole with a reinforcement on the inside of the body. This is the rear tie down point. I use ¼” chain with hooks at the rear of the car. One hook goes into the factory hole and does not have a keeper latch and one hook goes into the ring in the floor of the trailer and does have a keeper latch. I have the chains longer then needed so I can adjust the end tied to the floor for each side if it needs it. On the front I use the typical nylon ratchet strap to the factory points. I push the car forward as much as I can to take up the slack in the chains and then tighten everything up with the ratchet straps. I also have some cardboard taped on the nylon straps where they cross the front control arms as they tend to get some wear where they cross. I have no parking brake and tow out of gear. Make sure you use the correct grade of chain. The car is only around 2600# without you in it and even though Ranger and I went around about this fact, technically you are only holding ¼ of the weight of the car. So a ¼” chain rated for 3000# with a big safety factor is more than enough. I am also positive that most of the cars were delivered with a chain holding them down. Take a look at the over the road truck and see what is holding down the really big loads (steel coils, heavy equipment, etc.). This method also compresses the suspension so it is not working while going down the road. This has been argued both ways as being good and bad but I prefer not to have the car bouncing as the trailer bounces.

Just my ideas on the subject after towing these things for about 15 years.

Michael
#36
Great Lakes Region Series administrator

#2

Your rear fastening points must be in much better shape then the ones on my car. Mine are pretty flimsy.

Not trying to start a fight, but a heavy 2" strap is typically rated at 10,000 lb. I would encourage someone to pick up a 2" strap and ask themselves if 1/3 that much strength inspires confidence.

Easy to come up with scenarios where a multiple g’s are placed on the trailer. And every scratch on a piece of metal reduces it’s fracture resistance. Just as easy to use heavier chain, so why not?

I think that the standard for “working load” is 1/3rd “breaking strength”.

Not trying to convince you Michael. Am happy to agree to disagree

#3

I use the straps that go through my wheels and secure them in a cross wise fashion to d-rings on the trailer and ratchet those down tight. I do have the akg tow eyes on the bottom of my rear shocks but i wouldn’t want to use those to secure while towing.

#4

Ranger, I understand working load vs. breaking strength. I was talking working load. That is why I mentioned the safety factor. Think for a minute how other things are tied down or lifted. I have been involved with some heavy lifting that involved two large cranes hooked to the same piece of equipment. Do you think that every strap or sling was rated for the full amount of the load? Say you are picking up a 600K pound tank? Takes multiple slings of which each is not rated for 600K lbs. This same tank was tied to rail cars for delivery. How did they tie it down? Since we are talking about such small weight with the E30 it is easy to get carried away with what is perceived to be the only safe way to do it. The rules of statics still apply. You can even add in your dynamics as well and I think we are covered.

I have no problem with anyone disagreeing with my ideas. Along the way I have tried many different things to make this racing hobby work. Some of us just like to keep it simple and enjoy racing.

I would love to see the results of the toe plate experiment with the trailing arm tie down points.

Michael

#5

Statics and Dynamics. Man, are those words blasts from the past.

It’s the possible dynamic loading that makes me cautious.

The subject of strapping car’s down reminds me…Attached is a pic I took on I-95 en route to VIR the other day. Traffic was stopped for construction. Note that tow straps go over the vehicle, without really fastening to anything. [file name=IMAGE_048.jpg size=129761]http://spece30.com/media/kunena/attachments/legacy/files/IMAGE_048.jpg[/file]

#6

I’m a complete neophyte when it comes to towing a car in a trailer. I had attached straps to the front and back tow eyes and then to the D-rings on the trailer floor. The car seems secure enough, but then again I don’t know what I don’t know (if that makes sense). Can some kind soul please post a picture of how they secure their car so at least I stand a reasonable chance of actually getting it to the track!

Thanks,

Andy

#7

I criss crossed the straps I get from Summit racing rated at “Safe working load of this tie-down is 1,600 lbs.” and attached them to the four points mentioned by the OP. Using four gives me confidence my 3,000lb car will stay in place. Just in case I attach two more to the front and rear towing.
Since I had the time, and two old straps, I attached them according to my plan, plus two new ones. I used one old and one new strap in front and rear. Tied them down like always, and drove away, took the freeway for a mile. Got off at a gas station, pulled my pocket knife and cut the front old strap, and drove away back home, the car survived, moved a little, but didn’t fall off the trailer. At home I replaced the cut strap with a new one, cut the last old strap, and back on the freeway for another mile. Got off, the car moved a little in the back, but didn’t fall. I attached my last new strap to replace the one a cut, and got back home.
I can tell you if one of my straps fail, I will hear it, and I won’t drive a mile or more without out, that’s why I always carry two extra long straps, and two shorts. Better be safe than sorry.
BTW, when I see heavy equipment being carried on trailers, the chains are always crossing each other when they use two. When they use one chain either across the axle, or thru the wheels, which I think it’s insane.

#8

I don’t understand why anyone thinks it helps to cross the straps. The closer the 2 points you are tying together the better. They shouldn’t be straight down but angled out(or in). Just think how much more slack will be in you’re tie down if a strap breaks and the car moves over an inch with the straps crossed. A month ago I packed up half a dozen cargo containers with atvs, aviation ground power units, and rotorhead and engine trailers and chains don’t get crossed. It would be much better to tie your car straight down and put blocks to the front, back and outside of your tires than cross your straps. People worried about their suspension on a trailer are nuts, any force put into the suspension goes through the soft and gooey trailer suspension first.

#9

Michael,

I use the a very similar tie down method to yours. I use 2" straps all around. I use the factory tie down points in the front, while the rear is hooked to the subframe. In each case, they are connected to D-rings directly behind, or in front of, the points of connection on the car. Crossing the straps is usless, counterintuitive and just plain stupid.

I am not an engineer, but I do have a BS degree in Architecture, where I studied structural analysis. (I even slept at a Holiday Inn Express last night too.):silly: I also have experience rigging loads on construction sites and with lifting steel beams with a crane. You are correct in stating that each of the 4 straps is essentially performing 25% of the work, if done correctly. Furthermore, you are not lifting a 2700# car in the air…you are securing it to another object. Therefore, the load is substantially less than the actual weight of the car. I don’t worry too much about lateral movement of the car. Take into consideration the contact patch of the tires. They reduce potential lateral load even more. The only way it is moving sideways is if you take a side impact or maybe if you try to make some ridiculously abrupt maneuver. In such a case, you are most likely screwed anyway. We all should know enough about vehicle control to avoid overreacting and providing too much input to any vehicle.

Personally, I like to compress the suspension at least a little when towing. If the car is bouncing around on the trailer, you definitely have less control of your entire rig.

Perhaps the fear of the unknown is disconcerting enough to some to result in overkill, which is not necessarily a bad thing. I certainly have confidence in a 2" strap rated at 10k breaking strength. Especially after I personnally inspected it before each and every tow. I will continue to tow confidently with the method I have been using for the past several years.

#10

I put my rear straps around the rear subfrmae with axle straps. Car never moves and I never have any issues while towing.