[racingdwarf]

Ahh I can now reply to my own question after having a good hunt about on google I found the same question on a US short course forum, it appears that HPI did an upgrade at some stage to 5x11x4 but never changed the book.

Nice, as if you look at all the bearing sets on ebay they are all 5x10x4s so if you buy one it's more than likely not going to fit depending on the age of your truck, things that make you go Hmmmmm