Hi Andy, that makes sense. I did actually run a set of older Schwalbe Winter's (700 x 38) with studs and full fenders (SKS Longboards). They cleared, but there was a hint of rubbing of the studs against the fenders. I would not be using fenders if I installed the Big Apple's of course. Looking at the amount of space by the chain stays and also clearance around the fork, I would think the Big Apple 50's might work. I measured that in the narrowest part (at the chain stays), there is about 6-7 mm space remaining (either side). My 700 x 35 Racer's measure 31mm wide with the rims I am using. So, assuming that the 50mm width is an enthusiastic assessment by Schwalbe, perhaps the additional 15mm (7.5 on either side) would be sufficient?

Here is a picture showing how much room is left by the stays. I am not concerned about the fork as I can see there is lots of room there. The stays are the tricky bit! What do you think?