I'm thinking of putting 10 inch wheels on my boat trailer but am confused over which type. There appear to be two main types. Some are 145x10 and some are 500(or 520)x10. When I was driving Minis in the 1960's (that gives my age away), the former were radial tyres and the latter were cross plies. I thought cross ply tyres had gone for good. What is the difference and what is the advice about which to choose please?

if the tyre number is R10 they are radial. If it's B10 they are not and are rated to 50mph.

Go for 145 x 10, tryes still easy to get hold and cheap.

......and don't forget to have the trailer wheels balanced. You'll be astonished at the difference it makes.

Nick C

Towsure (mail order too - Google it) are probably the cheapest for new wheels. Check studs and centre sizes as I'm led to believe mini wheels are different.

I briefly used a trailer with mini wheels and 'proper' tyres and it seemed to give a much more stable and cushioned ride than one with the 'normal' trailer wheels.  
The stud PCD is the same on the mini wheels I've got,but the different offset requires longer stub axles, so not easily interchangeable.

In the good old days, the boy racers used to put alloy spacers on the stubs to increase the track. I'm sure these are illegal for cars now, but see no reason why they couldnt be used on a boat trailer. 
have just checked - http://www.halfords.com/webapp/wcs/stores/servlet/categorydisplay_storeId_10001_catalogId_10151_categoryId_165464_langId_-1
still seem to be available from halfords - maybe they are legal for cars still....