Seems there is a lot of confusion over how to find the relevant figures, so here's a couple of pics:
Vehicle VIN plate:
Can be either a metal plate, or a sticker, usually found on the slam panel (between the headlights) under the bonnet, or on the door frame on either the passenger or drivers door, sometimes you will even find it under a plastic flap in the front footwell carpet. Don't confuse with the sticker giving you the various tyre pressures for all the different sized tyres that may have been fitted to your vehicle. It will usually be smaller than the one pictured, with just the chassis number, and four lines of figures. They are not normally labelled so the order is important.
IMG_0973 by
Ollie and Sally, on Flickr
Trailer chassis plate:
Lots simpler, in this case the MAM (aka Gross weight) is 3000kg. Do not confuse with the plate that may riveted directly to the hitch/handbrake mechanism as this is often higher than the trailer, and indicates the design limit of the hitch and not the trailer.
IMG_0991 by
Ollie and Sally, on Flickr
If you don't have a chassis plate and want to use the tyre load rating, look for a number, usually in the range of 80-100, this is the rating. It will be in the format similar to 165/75 R14 84T, 84 being the load rating. You really should look for the plate though, as the tyres can often carry more than the trailer and it suspension is designed for.
Whilst you are looking at the tyres, you may as well look for the date code as its important and normally overlooked! Its recommended trailer tyres are changed at five years old as they degrade and perish before they wear out. I left mine until they were six years old, thinking that as the trailer had spent 4 of its 6 years in under cover storage, they would be good. They were not, three of the four were dangerously degraded and had bulged, but with no obvious signs of perishing. The tyre below is meant to be perfectly flat, and the previous weekend I had driven three hours on the motorway with the tyres like this:
IMAG0297 by
Ollie and Sally, on Flickr
The date code is sometimes hard to find, but should be in the format "DOT 3207". 3207 being the 32nd week of 2007. If you have a three digit number, DOT274, your tyres are pre 2000, making them a minimum of 11 years old. Scary!
Hope this helps
If ROG or Tallyho want to copy this into one of their early postings on p.1 then feel free.