Boat Trailer axle and bearing rated loads

[Peter T]

Hi all, as some of you might be aware, I am in the process of building a new trailer for Spindrift. In checking up on load ratings, it became quite confusing why there was so much difference in load rating between Ford and HT hubs, so I have found out all about it and this is it :
As a rule, Holden HT hubs and axles use wheel bearings known as "LM" bearings. Also, as a rule, Ford hubs use " SL" Bearings. The LM ones are rated to around 750kg whereas the SL are rated to 1500 kg. When I looked up the Tas Govt page on trailer compliance it stated that with loads over 750 kg, SL bearings needed to be specified. The difference between the two bearings is that the internal axle diameter on the SL is quite a bit larger than that of the LM. Both bearing sets have the same outside diameter, so either bearing will fit into either HT or Ford hubs. Because the SL bearings internal or axle diameter is larger, then that means that the actual axle, as well as the stub axle needs to be made from 45mm x 45mm square or 45 mm round bar whereas the normal HT axles with LM bearings can be made from 40mm x 40mm or 40mm round bar.
So, you can fit SL bearings to HT hubs so long as you have the 45mm axles instead of the 40mm ones. Other than the internal diameter of the bearings, there is no other difference between them.
So, I have ordered 45x45 axles, Galvanised HT disc brake hubs ( because I already had galvanised HT wheels ) with mechanical disc brakes which are fitted with SL bearings as well as 9 leaf galvanised slipper springs rated to 1900kg and will fit light truck tyres. This way, you can increase your load capacity from 750 kg per axle to 1500 kg so long as your springs and tyres rate equally as well or higher. I was going to use the single leaf Parabolic Spring which would be ideal for salt water environment but the highest rating of those is 1400kg and as I am using 3mm, 4 mm and 5 mm wall thickness for the steel of the trailer am not too sure what it's total weight will come in at and I thought that 1400 kg springs might be cutting it a bit close. You would not believe how hard it was to actually find someone who knew all about this, but at least now, we all know. Hope this helps people, especially if building a new trailer. I would strongly suggest that anyone with a single axle trailer measures their axle size so you can determine what load capacity you have.
Regards Peter T

[Ozzie]

That’s interesting stuff Peter and not surprising that it’s hard to get the right information on.

Vehicle standards for as long as I’ve been dealing with them are often grossly ambiguous and often these days seem to be focused on who to blame (read pay damages ) if something goes wrong. Can’t change your brand of wiper blades without an engineers certificate

Not home right now but with measure my axle when I am. I assume original trailers probably only complied with a lesser standard.

[Peter T]

Yes David, you are correct mate the SL bearings do stand for Slim Line and I reckon you are correct re the LM. Extra load bearing of the SL comes from them only fitting on a 45. mm axle where as the LM will only fit on a 40 mm Axle. LM rated to 750 kg, Sl rated to 1500 kg
Cheers Peter T