Many thanks Ben much appreciated, I have slackened those wagons with tight bogies - I think you mention this on your website, whilst this did help unfortunately it hasn't solved the problem. I will definitely set up a a length of straight track on a slight incline and try the hoppers one at a time, great idea. I wasn't sure whether it might be an idea to grease the axles?
Thanks Ben, great wagons though
Best,
Chris