38mm tires are not fat. I don't even consider the
Serfas Drifter fat at 2", for my bike 2" is just right. I have 1.5" Slickasaurus on it now and imo those are thin, not skinny, just thin. Fat is something like the
Vittoria Bomboloni 
For a road touring bike such as a Surly road touring bike, 38mm tires are fat.
On the other hand, I find 2" tires on my mountain bike as too fat and 1.5" as too thin. For my bike, I went in the middle and run 1.75" tires both front and back. The back rim is a custom built 40 spoke rim at a local bike shop about 10 years ago after breaking a few spokes in the original Mavic rim. Since then, zero broken spokes.
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Earth and sky, woods and fields, lakes and rivers, the mountain and the sea, are excellent schoolmasters, and teach some of us more than we can ever learn from books.
John Lubbock
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