Why do trailer wheel bearings wear out?

OK, so I've finally got round to doing some maintenance on the trailer. This year it has done a few long trips. Ballyholme to Kinsale (600 mile round trip), Ballyholme to Gosport (1100 miles) and Ballyholme to Galway (400 miles). On the way back from Gosport the left wheel strted to vibrate and a kindly mechanic said I would be lucky to get another 500 miles out of the bearing. Since then I've done another 800 miles but enough is enough and I am in the process of replacing both axle hubs.

But why do they wear out. My car has done 100k miles. Admittedly it has 17" wheels rather than 10" but that's still a lot more rotations than the trailer wheels have done. The loading on the car is higher per wheel than the trailer. The trailer stays dry (ie I don't use it to launch). I keep the tyre pressures good and am generally kind to it when driving. So why does my trailer hubs need replacing when to replace car wheel bearings is almost unheard of?

Alloys on your trailer? And a spoiler...

Agree about the wheels, though I suspect decent ones would just make them more likely to be nicked.

Trailers only tend to get very intermittent use. This causes several problems. When the bearings cool down after running, they draw in air, which has moisture in it. In cars with traditional taper roller bearings like a lot of trailers, this isn't a problem as the regular heating cycles tend to drive out the moisture. Trailers sit on the drive or in the boat park for weeks, sometimes months, between uses so the moisture starts corrosion. Trailer wheels are not usually balanced, which puts extra strain on the bearings. Most people don't adjust or clean/repack their bearings so the grease they run in is usually filthy and ancient. Add all that to the fact that most trailers in the UK run on 8 or 10" wheels, so the wheels rotate much faster than your car wheels, and a lot of people tow at stupid speeds, and they are bound to wear out quickly

The next point I have no real evidence for, but I believe that most people run their trailers with far too much pressure in the tyres. Think about it this way: the air in the tyre is there to support the loadand stop the tyre from deforming too much and overheating. An old Mini runs similar size tyres to a trailer with 10" wheels, and runs 26psi tyre pressures. Just on the weight issue, a loaded trailer with say 100 kgs of boat and rig might weigh 200kg, so well less than half of a Mini. Then there's the fact that the Mini's tyres also have to cope with power, steering and braking loads which will put loads more heat into the tyres. I reckon a trailer with the average dinghy on it shouldn't need much more than 18-20 psi for the tyres to work correctly. Anyone have any proper data on this? Don't forget that the pressure marking on the side of the tyre is a maximum at max load, so an absolute limit, not a service value.

If you want better bearings, take your old ones to any bearing supplier and he should be able to pull a set of Timken bearings of a shelf for you.

Neil

£22 for a new hub...mmmmmm remind me again how much the same unit for a car would be???

Think the answer may be out there somewhere