That LRS hitch is very similar to the standard fitment on Patrols which also has the same bolt hole pattern as the Defenders. It may be worth checking out the wreckers.
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That LRS hitch is very similar to the standard fitment on Patrols which also has the same bolt hole pattern as the Defenders. It may be worth checking out the wreckers.
Exactly the question that should be asked and one that I considered at length. What I could calculate was:Quote:
Originally Posted by nugge t
- the four M10 12.9 bolts that came with the swivel have a combined tensile strength design limit of approximately 14,800 kgf.
- Conservatively assuming that the remaining material (after additional drilling) beside the hole was 4.6 carbon steel it would have a tensile strenth design limit of approximately 9,000 kgf.
What I couldn't calculate was:
- The design loading limit of the cross member.
- The mode of failure or
- The point at which the base plate would fail (IMO probably around the base of the clevis).
Thus my conclusion was that:
- the load limit of the swivel recovery point was no more than 9,000kgf
- the limiting factor was probably the rear cross member (opinion only - I can't substantiate this)
- Snatch straps over 9,000Kg shouldn't be used = 8,000Kg snatch strap.
In conclusion, the question that needs to be answered is: what is the Recovery Load Limit of the rear cross member? Destructive testing can be done on somebody else's puma!
It would also be interesting to analyse the LRS hitch. IMO the result would depend largely on the quality of the weld and what heat treatment was applied after welding. Assuming that (a) the loop is 12mm diameter (b) the loop was the point of failure (is it???) and (c) the loop was made of 8.8 steel (is it???) and (d) the welds did not fail (hmmm....) that would give that hitch a tensile strength design limit of 2 x 5,700kgf = 11,400kgf. Personally, I think it would fail at the welds, yielding a lower design load limit.
Interesting... In truth, the issue that I've been struggling with is whether or not to install the towbar that I've got sitting in the garage simply for recovery purposes or not. Of course then I'd have to (a) compromise my departure angle and (b) calculate the shear strength of the hitch pin... based on more assumptions - and then I'd be wondering about rated towing limits vs recovery load limits.... Agggghhhhhh!
Then of course you need to ask the question: where do you want failure to occur? IMO the answer is the strap. Is the strap the weakest link in the chain? That depends on the design strength of the cross member.... Agggghhhhhh!
I recall reading somewhere that the chassis on a Puma is 2 mm mild steel suggesting that the rear cross member, except where it has been specifically reinforced, is not very strong. I guess that this is why current Defender towbars link back to the chassis rails for additional strength, by spreading any potential load across several points. I opted for the towbar recovery option but I have a D90, so the rear departure angle was exceptional anyway. I would have gone for jate rings but installing them necessitated removing the fuel tank first. Thought it was too much bother. Obviously not an issue with a D110.
Cheers
KarlB
:)
I agree with KarlB.You would have got away with a single fixture on the rear of a series.May get away with it on 110 or early Defender (wouldn't recommend it though).But the rear cross members on later models are made of very thin metal.Most people use the towbar hitch,as the towbar mounts back to the chassis rails on both side to spread the shock load,similar to what using Jate rings does when used in conjunction with a bridle strap.I think if you used the heavy welded type mount that you have pictured,and ran a piece of heavy plate across the inside of the rear cross member,with plates welded on the ends and mounted this to the chassis with High tensile bolts and used crush tubes in the holes in the chassis,you would have something fairly solid,and keep your departure angle,which is the problem with towbars.
Wayne
Keep an eye on this other thread for more ideas...........
County, front recovery points ...
Thanks LowRider and KarlB...I had read that as well but it all seemed heresay which was why I asked the question. Guess I need to get down and dirty and really check it out.
nugge t,
At a little over $300 the genuine LR tow hitch is still not a bad option. The entire arrangement sits nice and high and allows for the vehicles full maximum tow rating to be employed. As stated before, the load is spread over a number of connections and the square inset arrangement allows a vast number of "attachments" to be used. Recovery swivels, removable winch mounts, bike racks etc.
Front I've just gone for the aftermarket hooks shared attached to the chassis and bullbar. I like spreading the load in any case, so I opted for two and a bought a plasma/Dineema strop bridle to even the load on the front.
Saying all this it is still a Defender and I've only used the rear fetching "inferiors" from where they were stuck!
Cheers,
Lourens
Interestingly I have a genuine LR tow bar on my 130. It says not for recovery purposes, or words to that effect.
It's odd how it's rated for 3500kg for towing but not a recovery. I wonder what LR are thinking sometimes.
Just checked the spare OE towbar (Part No RAA608) I've got sitting in the garage. As per newhue's post it has "FOR TOWING PURPOSES ONLY" stamped underneath.
Whist there's plenty of options available to choose from I'm not aware of an official rated rear recovery point being available, so no matter which way you choose you'll be guessing what it can withstand and where the failure will occur if recovery forces exceed the capability of your setup. Yes, some choices are significantly better than others, but at the end of the day you're still left guessing as to how strong it really is.
I have a LRA tow bar on my 2010 Puma station wagon and I feel happy to use it for recovery purposes.
I suggest people have a good look as to how it is fixed. I doubt that it will pull off before a recovery strap breaks.