Amazing. Thanks for the replies everyone! Oops, I forgot to mention that the size of the bike is 54cm. I've had a look at a couple of bike shops and they only seem to stock dirt cheap ones for mamacharis. They only have an extremely limited selection of good racks so I thought buying online would give me much more choice.

dellwilson, thanks for the link! It's good to see concrete proof like that, however Tubus racks are a bit too expensive for me.

Clem von Jones, thanks for those links! It's definitely made me understand how to roughly see where they sit on the back of a bike.

I can't seem to find any Axiom racks on any online websites in Japan, so unless I can find an online dealer that ships to Japan for cheap, I think I may have to pass on those. I'm give the Bontrager Back-rack deluxe a look when I'm at work tomorrow. In an ideal world I'd have enough money to buy front and back racks with 4 panniers to put on them. For now, I'm going to tough it out with just a rear rack and panniers until I have enough money to buy the front set. I've only had to bike for a week and I still have lights and a lock on my shopping list along with a bunch of other things. Aaarg!

So wider racks can cause more instability?