iti20090,
Normal rims used on the Tamiya mini are zero degree off set. The Tamiya rims are the same 12mm hex, so I would think the standard zero's would be the answer. You would also get away with the 3mm offsets but the other forget it.
BTW,
I do not own a HPI Cup racer. However someone in the Cup Racer thread maybe able to answer this question.
Regards,
Calvin.