Trailer Tie Downs

#1

Having just purchased my trailer this week, I’m now staring at the underside of the car wondering how to attach it. The two front tow hooks are obvious and a no-brainer, but I don’t know what to do on the ass end as there is only the one hook. I’d like to use a method where I can use a pre-made length of chain to attach the rear, then inch the car front and secure it with ratchet straps in the front as it would make loading faster and easier. So how are you-all doing it?

No debates on hooking to the body vs suspension please. I waded through that on another forum already. Summation: pluses and minuses to both.

#2

Your approach seems reasonable to me. I’d get a chain (and hooks?) that can handle 4k lbs if the single chain is going to hold the entire rear. A 3k chain is likely just rated for a 3k static load and a sudden load on the chain could go way over that. A 5k chain would be better.

Where was it that you read about the body vs. suspension? I’d be interested in reading that.

I’m not so sure I’m doing this very smart. I’m running straps thru my rear tires and then crossing the straps to the opposite anchor points. Therefore each rear tire is pulled down in such a way that could cause positive “toe”. But I figure that a car’s wheels are subject to some pretty serious side loads on the track, and a couple hundred gentle miles on a trailer can’t be nearly as severe.

That being said, just how dumb of a rear securing solution is my crossed strap tire-fastening technique?

#3

Use the chain up front and use straps wrapped around the rear sub frame on each side in the rear. This way you won’t have to worry about jacking up your alignment and the straps are easier to reach.

#4

I use chains in the rear and ratchet strap in the front. Just behind the tires on the inside of the fender there is a elongated hole that is the factory tie down. I have some chain (I think 1/4") with a hook (took a while to find one that would fit) that I hook in the hole one on each side. The other ends I hook to the tie down on the floor of the trailer with some excess chain to make it adjustable if need be. On the front I use the standard Lowes heavy duty ratchet straps. Be careful as the strap will rub the front control arm. I have wrapped some cardboard around the strap at this point.

There are some eyes that some add to the lower shock mounts but I don’t like these as I think if you have the straps at the wrong angle you have the potential to bend the trailing arms. Same goes for hooking through the wheels. If you use these methods make sure you have the angle of the straps going straight back or to the outside.

Keep in mind that the chain does not hold all the load but only 1/4 of it. I have used the 1/4 inch good quality chain for 3 or 4 years now with no problems.

Michael
#36

#5

ilateapex wrote:

[quote]
Keep in mind that the chain does not hold all the load but only 1/4 of it. I have used the 1/4 inch good quality chain for 3 or 4 years now with no problems.

Michael
#36[/quote]

The chain only needs to hold 1/4 of the load when all is going as expected. It’s the unexpected that you have to prepare for. I don’t have much of a background in towing or trailers, but speaking as a mechanical engineer, I’d provide a safety factor sufficient that each tie down is capable of supporting the entire static weight of the car. And that doesn’t even get into dynamic situations. f=ma and it’s the “a” that will kick our ass.

#6

I just picked up a trailer too, so I had to sort this out 2 weeks ago. I used ratchet tie downs to the factory holes in front AND rear. My car is a '90 model, maybe the factory holes on the chassis are inconsistent between years?

#7

I hear you and as an engineer myself, I would like to see how you plan to keep that car on the trailer with only one point tied down. I don’t think it would matter how much that one chain or strap would hold, the car won’t stay. I am all into safety factors and such and even carry two spare tires for the trailer. When things go bad not much will keep the car from getting damaged. Looking in the trusty Fastenal catalog, 1/4" grade 70 chain has a working load limit of 3150# The Grade 43 high test chain has a WLL of 2600#. Both are more than the total weight of my car without me in it.

I have towed many different cars on many different trailers and the method I stated seems to work fine for me.

YMMV

Michael Osborne, P.E. (Prick Extraordinaire according to the guys I work with :unsure: )
#36

#8

The rear factory holes in the fender will break eventually over time especially if there is some rust back there. I never had a problem on my E30 M3 in 5 years but they were starting to bend. I use the same factory holes on my spec E30 but had them reinforced slightly. YMMV.

#9

Very true Simon. I had to reinforce mine on the old ITS car as well.

Michael

#10

ilateapex wrote:

[quote]I hear you and as an engineer myself, I would like to see how you plan to keep that car on the trailer with only one point tied down. I don’t think it would matter how much that one chain or strap would hold, the car won’t stay. I am all into safety factors and such and even carry two spare tires for the trailer. When things go bad not much will keep the car from getting damaged. Looking in the trusty Fastenal catalog, 1/4" grade 70 chain has a working load limit of 3150# The Grade 43 high test chain has a WLL of 2600#. Both are more than the total weight of my car without me in it.

I have towed many different cars on many different trailers and the method I stated seems to work fine for me.

YMMV

Michael Osborne, P.E. (Prick Extraordinaire according to the guys I work with :unsure: )
#36[/quote]

Internet hiccup ate my fabulous response. The Cliff Notes version is:

Good to talk to a person with a real education.

Straps degrade because dirt and stress causes microfraying. Chain strength degrades because of scratches in high Moment areas and corrosion.

The tie-down certainly have to withstand short duration Impulses beyond their designed static bearing limit. Those impulses hasten the above degradation.

I’m better at sounding like I know what I’m talking about, then I am at genuinly knowing what I’m talking about. So as usual, I pulled this all out of my butt.

I’m a wuss so I use 4 straps each with a 3000lb capacity. I’ll replace them every couple of yrs, I figure. But I’m sure there’s a better way to strap a car on than what I’m doing, so I’ll be looking at how other folks are strapping their cars on.

#11

Good to talk to a person with a real education.

[/quote]

You may be very shocked at some of the education levels you will find at the track. I never assume i know more then the next guy and listen to them all. Sometimes it is education and sometimes it is experience. We can learn from both.

Michael

#12

For the Record:

I’m using four 3,000 Lbs. ratchet straps. 2 in the front that cross (because of trailer D-ring locations) and connect to the factory points that are attached to the frame. In the rear I loop over the sub-frame.

I’ve never had any issues.

#13

ilateapex wrote:

[quote]Good to talk to a person with a real education.

[/quote]

You may be very shocked at some of the education levels you will find at the track. I never assume i know more then the next guy and listen to them all. Sometimes it is education and sometimes it is experience. We can learn from both.

Michael[/quote]

It’s not a matter of knowledge or skills. As a hard science type you went thru hell to get your degree. That is what I salute.

If I’d a had an ounce of sense my diploma would say Women’s Studies and would represent a dim recollection of beer and sports-sex. Oh for a chance to do that one over.

#14

Ranger wrote:

[quote]
Where was it that you read about the body vs. suspension? I’d be interested in reading that.[/quote]

www.corner-carvers.com
I did a search for “trailer tie downs” or something. There are a couple good threads over there if you even just use “trailer” as your search word. There is debate over strapping through the wheels, fastening to the suspension vs the chassis, shock damage due to trailering, etc. though I’m not sure there is a true gospel concensus on some of it, but food for thought anyway.

Keep the ideas coming. Right now I like the sound of the chain to the front hooks and straps around the rear subframe.

#15

Mine are to the factory holes in the front - on the shock bolts in the back via eyelets from AKG Motorsport (the place I got all my engine/tranny mounts too). I do not cross them - straight back. I used to cross them - until someone smart told me why not too. Seems to be like religion on that - you feel strongly one way or the other, and you will not convince anyone to change.

No issue with alignment changes in the rear after 3 years of towing this way - and I crank them down. Like Ranger - 3000 lb. straps - and we try to clean them (spray them down with water) often to get the dirt out of them. I tuck the front extra in the driver doors, and the rear extra in the trunk when traveling so they don’t whack around.

#16

Crossing the straps doesn’t allow the car to shift side-to-side if the straps loosen. I’ve seen the aftermath of a failure to do that with a tractor and it wasn’t pretty!

Attaching the straps close to the wheels, so that the body is sprung, reduces the peak loads on the straps and doesn’t place the suspension in a state of compression. Attached in this fashion there’s less chance of the car shifting when the trailer sees large vertical accelerations.

#17

jlevie wrote:

[quote]Crossing the straps doesn’t allow the car to shift side-to-side if the straps loosen. I’ve seen the aftermath of a failure to do that with a tractor and it wasn’t pretty!

Attaching the straps close to the wheels, so that the body is sprung, reduces the peak loads on the straps and doesn’t place the suspension in a state of compression. Attached in this fashion there’s less chance of the car shifting when the trailer sees large vertical accelerations.[/quote]

This would nicely address the issue of “impulse” loads peaking over the design tolerance of the chains/straps.

#18

jlevie wrote:

[quote]Crossing the straps doesn’t allow the car to shift side-to-side if the straps loosen. I’ve seen the aftermath of a failure to do that with a tractor and it wasn’t pretty!

Attaching the straps close to the wheels, so that the body is sprung, reduces the peak loads on the straps and doesn’t place the suspension in a state of compression. Attached in this fashion there’s less chance of the car shifting when the trailer sees large vertical accelerations.[/quote]

Like I said - it’s like religion. His expanation was that the car is not likely to shear - it will roll forward or backwards. The straps loose a very high percentage of their strength when the pull is at an angle (crossed) vs. straight. He said the force to make the car shear (the tires slide side to side) is higher than the straps would hold anyway.

He suggested I look at anything tied to a flat bed truck by a trucker (I know - insert a trucker joke here) - I have looked - never seen straps crossed - always straight.

I did have to tow my E36 318 one time - and you need to cross the straps with the E36 because of the way the J-hooks fit into the frame. The E30 doesn’t have that problem.

This thread has some good stuff in it too - http://forums.bimmerforums.com/forum/showthread.php?t=528228

I’m sticking with the straight route.

#19

jlevie wrote:

[quote]Crossing the straps doesn’t allow the car to shift side-to-side if the straps loosen. I’ve seen the aftermath of a failure to do that with a tractor and it wasn’t pretty!

Attaching the straps close to the wheels, so that the body is sprung, reduces the peak loads on the straps and doesn’t place the suspension in a state of compression. Attached in this fashion there’s less chance of the car shifting when the trailer sees large vertical accelerations.[/quote]

Consider what happens when one strap fails. Hit a big bump, car moves in the direction of the remaining strap as it is in tention, now remaining strap is loose.

Michael

#20

Tie down method aside, how much tension should I put in the straps when cranking down on the ratchet? Until I can’t crank it anymore, just get out the slack, or somewhere in between?

Last haul I used the “get the slack out” method and it didn’t go anywhere, but I could have just been lucky.