50mm vs 2" towballs

[JohnO]

Hi all, the US has several standard towball sizes - 1 7/8", 2" and 2 5/16".

NZ commonly has 1 7/8" and 50mm.

Now 50mm != 2" (50.8mm)

So a 2" American trailer coupling is slightly loose (0.4mm either side) on a NZ 50mm ball.

Is this permitted? Can anyone point to any rules or references to this? Or a reported occurrence of such a combination becoming detached due to the mismatch?

I can't find anything, even on nzta which doesn't even prescribe specific ball sizes.

[peterwn]

See:
http://www.towbarfactory.co.nz/index.php?page_id=19 and
http://www.towingguide.com.au/content/couplings.html

50mm is mandatory in Australia.

It would seem to me that NZTA would dearly love to standardise on the 50mm size to be compatible with Australia (it originated in Europe), but the large 'base' of trailers with 1 7/8 couplings would make a mandatory changeover impracticable. The issue probably sits perpetually in NZTA's 'under consideration' basket*.

Presumably one day, a 50mm coupling on a 1 7/8 ball will come off AND the safety chain will fail with dire consequences and caustic comments from the coroner.

Presumably the 2 inch American size would have found little application in NZ, so the chance of a 2 inch coupling being used on a 50mm ball is remote.

* see:
http://www.imdb.com/title/tt0751822/quotes

[Pooh]

"JohnO" <john...@gmail.com> wrote in message
news:f752b56f-0f71-48cd...@googlegroups.com...

Isn't that part of the reason for safety chains?

Would it be possible to change the coupling so both parts are a good match?

Pooh

[JohnO]

On Wednesday, 27 November 2013 11:27:22 UTC+13, peterwn wrote:
> On Wednesday, November 27, 2013 10:35:59 AM UTC+13, JohnO wrote:
>
> > Hi all, the US has several standard towball sizes - 1 7/8", 2" and 2 5/16".
>
> > NZ commonly has 1 7/8" and 50mm.
>
> > Now 50mm != 2" (50.8mm)
>
> > So a 2" American trailer coupling is slightly loose (0.4mm either side) on a NZ 50mm ball.
>
> > Is this permitted? Can anyone point to any rules or references to this? Or a reported occurrence of such a combination becoming detached due to the mismatch?
>
> > I can't find anything, even on nzta which doesn't even prescribe specific ball sizes.
>
> See:
>
> http://www.towbarfactory.co.nz/index.php?page_id=19 and
>
> http://www.towingguide.com.au/content/couplings.html

Yeah, but neither covers my question re 2" tow coupling on a 50mm ball and I'm not asking whether a 2" coupling can safely sit on a 1 7/8 ball.

>
> 50mm is mandatory in Australia.
>
> It would seem to me that NZTA would dearly love to standardise on the 50mm size to be compatible with Australia (it originated in Europe), but the large 'base' of trailers with 1 7/8 couplings would make a mandatory changeover impracticable. The issue probably sits perpetually in NZTA's 'under consideration' basket*.

They just put a sunset clause on existing 1 7/8 installations and prohibit new trailers with it. Most trailers can be fairly easily converted as can most tow balls.

>
> Presumably one day, a 50mm coupling on a 1 7/8 ball will come off AND the safety chain will fail with dire consequences and caustic comments from the coroner.
>

I am sure it has happened already, more than once. Most people would put a 50mm coupling on a 1 7/8 ball and not even know until it pops off on a large bump on the road. But the mismatch of 50mm on 1 7/8 is greater at 2.4mm than the 0.8mm between 2" and 50mm. A 2" coupling on a 1 7/8 ball is the worst of all scenarios being 3.2mm oversized.

>
> Presumably the 2 inch American size would have found little application in NZ, so the chance of a 2 inch coupling being used on a 50mm ball is remote.

Actually there are quite a few of them as lots of people are importing trailer boats from the US, and it seems there's no regulation or law that mandates changing the coupling to 50mm. There should be, but unlike vehicles with strict compliance rules there's nothing for trailers. As you say, they seem to have lazily left it in the too-hard basket and this inaction may lead to a tragedy.

>
>
> http://www.imdb.com/title/tt0751822/quotes

LOL!

[peterwn]

The ball is the easier item to change (assuming the threaded stud fits the hole in the towbar).

[JohnO]

Agreed, but then you have an orphan ball and an orphan coupling.

[JohnO]

On Wednesday, 27 November 2013 11:43:49 UTC+13, Pooh wrote:
> "JohnO" <john...@gmail.com> wrote in message
>
> news:f752b56f-0f71-48cd...@googlegroups.com...
>

<snip>

>
> > I can't find anything, even on nzta which doesn't even prescribe specific
> > ball sizes.
>
> Isn't that part of the reason for safety chains?

That and clowns not locking down their couplings!

>
> Would it be possible to change the coupling so both parts are a good match?
>
> Pooh

Yes, and I think it should be a requirement for WOF to have done so!

[Me]

I'd dump the 2" fitting, it might only be 0.8mm, but I don't think
having free-play is a good idea. The regs may not require it under 2
tonne, but IMO double safety chains of as short as possible length,
attached "crossed over" should be mandatory on all trailers.

For a replacement 1 7/8 or 50mm or two-way fitting, check this site:
http://transitengineering.co.nz/index.php?main_page=index

These guys are very reasonably priced compared with the likes of Trojan,
and are very good to deal with. They make really nice machined alloy
twin SS piston brake calipers for boat trailers etc.

Imported trailers are likely to cause all sorts of future compatibility
problems, from finding brake parts, bearing/stub axles etc, suspension,
though in saying that, we get so well and truly fleeced for many of
these parts in NZ, that it's probably easy enough and not more expensive
to buy stuff on Ebay etc, and get it shipped over.

I just bought 2 pairs of new 1500kg duratorques, which cost me nearly
$1200, "retail" was over $1500, cost in the US for equivalent capacity
torsion axles about= $500. But it would have been a major PITA
modifying the trailer to get them bolted up.

[JohnO]

Thanks for the link and recommendation, Me!