question for DOT "experts" on safety chains

[ampsucker]

Hey all ! Hope your doing great!

Took delivery of new 20' trailer last week. In going over it now that the weather is better around these parts, I'm wondering about the safety chains that came with it. The trailer is rated for 7,000 lbs with a 2" bulldog coupler. My understanding of the SAE J684 hitch spec is that each safety chain must be independently able to carry the full load of the trailer by itself and that there must be two such chains (double failsafe). From looking around, that would mean we are talking about at least a 5/16" grade 70 transport chain with similarly rated latching hook. I think that size chain is good for around 4,700 lb working load limit, so actually, it would need to be a little better to get up to the 7,000 lb capacity of the trailer.

Am I understanding this correctly? I realize the loads on the chains could be quite a bit more or less than the weight of the trailer should the hitch ball ever fail (lateral jerking, jack catching a ridge in the road surface, etc.) but is this basically what the spec is calling for? They supplied two chains with no markings that appear to be 1/4" links with soft metal latching s-hooks. I'm not buying that is good enough.

For what it's worth, I mounted 9,000 lb d-rings to my towing vehicle's class iv hitch so these chains will be attaching to something substantial. The draw bar on the truck is rated for 10,000 lbs after figuring the 4" drop as is the hitchball.

Thanks....

 

[Rara Avis]

Hey all ! Hope your doing great!

Took delivery of new 20' trailer last week. In going over it now that the weather is better around these parts, I'm wondering about the safety chains that came with it. The trailer is rated for 7,000 lbs with a 2" bulldog coupler. My understanding of the SAE J684 hitch spec is that each safety chain must be independently able to carry the full load of the trailer by itself and that there must be two such chains (double failsafe). From looking around, that would mean we are talking about at least a 5/16" grade 70 transport chain with similarly rated latching hook. I think that size chain is good for around 4,700 lb working load limit, so actually, it would need to be a little better to get up to the 7,000 lb capacity of the trailer.

Am I understanding this correctly? I realize the loads on the chains could be quite a bit more or less than the weight of the trailer should the hitch ball ever fail (lateral jerking, jack catching a ridge in the road surface, etc.) but is this basically what the spec is calling for? They supplied two chains with no markings that appear to be 1/4" links with soft metal latching s-hooks. I'm not buying that is good enough.

For what it's worth, I mounted 9,000 lb d-rings to my towing vehicle's class iv hitch so these chains will be attaching to something substantial. The draw bar on the truck is rated for 10,000 lbs after figuring the 4" drop as is the hitchball.

Thanks....

Safety Chains
Safety chains are a requirement and should be crossed under the tongue of the trailer so that the tongue will not drop to the road if it becomes separated from the hitch. Always leave enough slack so you can turn. Never allow the safety chains to drag on the ground and never attach the safety chains to the bumper.

Trailer Classification: Safety Chain Breaking Force-Minimum

Class 1: 2000 lbs (8.9 kN)
Class 2: 3500 lbs (15.6 kN)
Class 3: 5000 lbs (22.2 kN)
Class 4: The strength rating of each length of safety chain or its equivalent and its attachments shall be equal to or exceed in minimum breaking force the GVWR (Gross Vehicle Weight Rating) of the trailer.

 

[SPYDERLK]

Safety Chains
Safety chains are a requirement and should be crossed under the tongue of the trailer so that the tongue will not drop to the road if it becomes separated from the hitch. Always leave enough slack so you can turn. Never allow the safety chains to drag on the ground and never attach the safety chains to the bumper.

Trailer Classification: Safety Chain Breaking Force-Minimum

Class 1: 2000 lbs (8.9 kN)
Class 2: 3500 lbs (15.6 kN)
Class 3: 5000 lbs (22.2 kN)
Class 4: The strength rating of each length of safety chain or its equivalent and its attachments shall be equal to or exceed in minimum breaking force the GVWR (Gross Vehicle Weight Rating) of the trailer.

Good pointers. Wow! those breaking strengths are low compared to any reasonable chain - - Gr70 1/4" is 13K# and 5/16" is 19K#. Hooks and hook points are often the weak place.
larry

 

[ampsucker]

Thanks for the info, Paul.

Still a point of confusion, maybe you can help this flat footer unnerstan....

Difference between "working load limit" and "breaking force"?

At the local hardware store, the bucket of chains holding the 5/16" grade 70 transport chain lists working load limit of 4,700 lbs. That is not for overhead lifting, so I assume that is force applied in any direction and they just don't want the liability or quality control costs of making sure it won't squash someone from above.

In your spec on safety chains, it seems to call out the "breaking force" as opposed to the working load limit. Do we know what kind of safety factor is built into the breaking force over and above the working load limit? It seems to be quite a bit higher, which may mean the chain they provided is adequate per the specification.

Maybe someone could post up breaking strength and load limits for various types and sizes of chain? I've googlized all this, but the amount of information is just too much to wade through for me right now.

Thanks!

 

[SPYDERLK]

Thanks for the info, Paul.

Still a point of confusion, maybe you can help this flat footer unnerstan....

Difference between "working load limit" and "breaking force"?

At the local hardware store, the bucket of chains holding the 5/16" grade 70 transport chain lists working load limit of 4,700 lbs. That is not for overhead lifting, so I assume that is force applied in any direction and they just don't want the liability or quality control costs of making sure it won't squash someone from above.

In your spec on safety chains, it seems to call out the "breaking force" as opposed to the working load limit. Do we know what kind of safety factor is built into the breaking force over and above the working load limit? It seems to be quite a bit higher, which may mean the chain they provided is adequate per the specification.

Maybe someone could post up breaking strength and load limits for various types and sizes of chain? I've googlized all this, but the amount of information is just too much to wade through for me right now.

Thanks!

did you see post 3. looks like a factor of x4. The difference is to provide enuf surplus tensile to endure the force spikes caused by acceleration/jerking against the inertia of the load mass.
larry

 

[ampsucker]

thanks for the clarification. yes, i did see it, but wondered if it was a flat 4:1 ratio across all sizes. it seems to be.

did a little wading and came up with this for anyone else who is interested.

ASTM 80 grade 70 transport:

link size WLL Breaking Strength

1/4" 3,150 x4
5/16" 4,700 x4
3/8" 6,600 x4
7/16" 8,740 x4
1/2" 11,300 x4


ASTM80 G30 Proof Coil Chain

1/4" 1,330 5,300
5/16" 2,000 8,000
3/8" 2,800 11,200
7/16" ? x4
1/2" 4,800 19,300


ASTM80 G43 High Test Chain

1/4" 2,600 7,750
5/16" 3,900 11,600
3/8" 5,400 16,200
7/16" ? x4
1/2" 9,200 27,600

 

[txslowpoke]

It depends on the grade of chain you buy as to the safe working load, typically the across the board breaking strength is considered 5x the safe working load for the size of chain you use.
Where I work( A company that manufactures wire rope/chain slings and nylon slings) We sell many grades of chain. You also have to factor in foriegn and American made.......American made is better/stronger but costs more. For tow chains I use 3/8" grade 70 or "system 7 " chain, safe working load of 7700lbs, multiply x 5 and thats the breaking strength. For over head lifting quality you have to go Alloy chain. Just remember your chain is only as strong as your hook. You can have a 7700 lb chain, throw on a 3000lb hook or coupling link.............you need to match hook/coupling link/chain in weight ratings.
On our delivery trucks, which are 3/4 tons and we pull tag trailers I use the grade 70 3/8" chain, with a clevis style slip hook with latch at each end. Hook that end to a 3/4" bolt type anchor schackle that is attached to the factory hitch. I have 10 k D rings welded to the tongue of trailer and the the chain attached via a 3/8'' alloy coupling link. So in theory if the unthinkable happens we are covered, because the weak link in this setup is the factory safety chain hookup point.

 

[SPYDERLK]

thanks for the clarification. yes, i did see it, but wondered if it was a flat 4:1 ratio across all sizes. it seems to be.

did a little wading and came up with this for anyone else who is interested.

[Snip]
ASTM80 G43 High Test Chain

1/4" 2,600 7,750
5/16" 3,900 11,600
3/8" 5,400 16,200
7/16" ? x4
1/2" 9,200 27,600

Interesting that G43 stands out at only a 3:1 ratio. Probably cuz it can just yield and absorb rather than store energy. You get a chance to see the links stretching.
larry

 

[Skyco]

There theoretically shouldn't be any difference in strength between imported chain and American made chain for any given grade. If it meets the spec then it should meet the spec, unless someone is cheating. Which would not surprise me.

ampsucker- I'm also curious how you attached your D-rings to your hitch?
FWIW most hitch makers prohibit welding to their hitches because they are heat treated. I know my class V receiver hitch is that way.

One other safety chain thing I see is trailer manufacturers welding the last link in the chain to the trailer frame. Also a bad idea because the welding heat just made that link the weakest link in the system The chain should be attached without welding the chain, there are little doodads I've seen in trailer supply catalogs just for that, a piece of rod with a kink in it that is welded to the trailer with the chain captive in it.

 

[ampsucker]

thanks for all the replies! good to get some input on this topic.

i did not weld my d-rings to my hitch. my tow rig is an 04 tundra and it comes from the factory with a pretty decent tow package and receiver hitch. i left all the factory hitch stuff alone and bolted two 10k d-rings to the tube body of the hitch between each frame mount about 8 inches to the left and right of center. that way i still have the factory 2" receiver with the little rinky dink safety chain loops they put on. it's all intact and if anything fails, it won't be coming back on me. i used two existing holes in the tubing and punched on up through the top of the tubing for those and then drilled two more holes and used two 3/8" carriage bolts on each d-ring so they should be stronger than the chain attached to them. i'll probably use the little factory safety chain loops to attach my breakaway trigger wire.

on the connection to the trailer, the manufacturer did not weld the last link of the chain to the trailer, but used what looks like about 4-6 inches of bent 3/8 or 1/2 rod and just welded that to the trailer with the end link speared by it. i think that's a pretty good way to do it as long as the welds are good. that's a good point though about weakening the chain if you heat it up.

i had a pretty good laugh when the dealer delivered the tractor. it came on a little, short, single axle trailer. the wheels were about half flat looking from all the weight. i pointed out it was close to a 3,000 pound load plus the trailer itself on what looked like two radial car tires and a 3500 lb axle, if that. it was so short he just had the bucket sitting up in the air over the tongue of the trailer. he was like, yeah, i know that wasn't a legal way to tow it, but that's the only trailer we had free. apparantly he had just gotten a ticket from kansas DOT for improperly tying down an even bigger load, so he knew he was pressing his luck. whatever, i guess it made it here and nobody got hurt, so that's what matters!

really drives home the point that there are a lot of unsafe loads out there. be careful and watch out for the other guy who isn't!

amp