I have a Trek 1000c with the stock 700cm 28c tires. I just took my 1 year old son out for his first ride in the trailer this weekend. It went well, and he had a blast, so I'm looking forward to riding with him a lot more.
One thing I noticed though, even though I had the rear tire aired up to the recommended PSI, once I hooked up the trailer and got rolling, I noticed that the tire was squashing under the added load.
My question is: is 28c too thin? What size should I consider? I'm not even sure what the max size my rims/brakes will support, but i'm afraid that I'll wear the tire out or risk flats if I keep riding with it.