I'd be fitting as big as tires as I could for Japan, you'll probably find yourself riding on the footpath/sidewalk more than you would normally expect. Because the truck and car drivers are so nice to you, you end up trying to be as nice as you can back and make things as easy as you can on them, especially on narrow roads. There are sidewalks in places you wouldn't expect, way out in the country. The sidewalks have a very big curb and big dips at driveways, plus there are some hard core grasses that mess with them a bit.