How much can a "light touring" bike carry? I'm looking to go N+1 with a bike I can use for bad weather and fetching groceries.  (Actually 1+1 since I gave my previous bad weather commuter to my SO.)  I've been procrastinating, but today I picked up my biggest ever load of groceries in my backpack and weighed it at 28 pounds when I got home.  Carrying that much on my back wasn't pleasant or safe, but I can see needing to pick up a load like that again.  At the same time I'll most often be riding the bike with nothing more than a laptop, so I don't want a heavy-duty touring bike.  Will any "light touring" bike like a Raleigh Clubman or similar be able to carry thirty pounds on the rack, or do I need to be careful about picking an especially sturdy bike?
