The biggest I could fit was a 26. 27 was borderline - seemed just a little too tight for me. I guess a smaller spur would solve the problem ( smaller spur = smaller pinion right? ). Is there any advantage to having a larger spur gear?

Also, I'm using TRC tires. I had to trim the lower pod on the left side for clearance. Should I be shimming them out or was trimming the right thing to do?