I find the variances size designations among different tire brands fascinating challenging to deal with. I took the rear wheel with a Chinese Chao Yang tire (47-406 20x1.95 size designation) off my Zizzo and it would not fit my Nano. The tire hit the brake bridge before I could get the axle in the drop outs. On the other hand, I just replaced the factory tires on my Nano with Continental Ride Tours also sized 47-406 but designated as 20x1.75 and they fit with about 1/4" clearance under the brake bridge.

I always knew tires varied in actual size between different brands but the amount of the differences is still surprising to me. It's all part of the fun of upgrading a bike. I guess that is why BD states that some but possibly not all 20x1.75 tires will fit. And 20x1.95? That is a real crap shoot.