Diamond Back Haanjo Carbon - Max Fender Size?

If you want to be a safe, a 35mm would have lots of space.  When I looked in shops and tried with what I had on hand, it was much harder for me to find fenders wide enough for my tires. 

I have 650b wheels and 47mm WTB Byways now and there are miles of clearance.  I've done some huge rides this year and will be doing the DAMn in a few weeks. This is a great bike if you're comfortable disassembling and reassembling the bike (it came dry so I relubed most stuff and tuned it up before racing).  If you don't feel comfortable doing that labor, you'll save enough to justify the extra expense.