Here's some pics of my Xootr in it's current guise with 520 wheels. I say 'current' as I'm about to switch back to 406 wheels for a while. The wheels are a Velocity Uriel wheelset from Airnimal.
Attachment 202925
Years back Peter sent me a photo of a track-legal fixie swift with similar sized wheels that a couple of guys were racing on at velodromes, and since then I've always thought the swift looked better with bigger wheels.
The second pic shows the front-end, which is quite neat with Airnimal carbon forks, a standard road caliper. The forks give a nice ride - a definite improvement over the standard forks, plus of course they are lighter. With a bracket (simple to make) the forks will take 406 or 451 wheels, as can be seen in the recent photo posted of me riding in the Smithfield folding bike race.
The next photo shows the new bottom bracket shell I had welded under and behind the original. The larger wheels raise the bottom bracket so it's quite hard for me to touch the floor at traffic lights. But that's not the main reason I did this -it's because the swift's top tube is about 2 inches too short for me to get the stretch I need with a normal length stem. Also the seatpost angle on a swift is a 72 deg - to get my ideal position I need a 73 with zero layback post and to get that position with the standard BB I had to firstly switch to a i-beam post/saddle which allow more forward position, and set it at the most forward possible position. While my correct position was possible, I ended up breaking the rail on the i-beam saddle due to the leverage.
The picture above also shows how the rear wheel is very close to the frame (and the rear axle has to go quite far back in the track ends to get the wheel in, but the brake point is fine and a standard road caliper works). Also with cranks spinning so much further back they can hit the chainstays under power and you can see in the photo how I've had to file a wedge off the end of the crank by the driveside pedal to fix this. The wires to the BB are because it's an Ergomo power meter.
Finally, the bars and where I've chosen to put the drinks bottle. I have dried a behind-the-saddle position but the bottles kept jumping out over bumps. Dura-ace STI levers have been excellent (but note when using my lower BB shell I can't run a front mech as chainring is in the wrong place).
With the larger wheels you don't need such long stem riser to get the same position, but as you can see I still need lots of aheadset spacers here under the non-QR stem riser.
In the next week or so I'm converting back to 406 wheels and plan to run a front mech for the first time.
Oops - just forgot that I should have photographed the bike folded. As you can imagine it's not a compact package, but it makes no difference to my own commute, which is on trains with plenty of room. I'll post a photo later in the week.
The inspiration to run 520 wheels came when I broke my swift forks, and had to borrow a folding bike off a friend. That bike was an Airnimal and I liked the ride a lot and for me it was faster and smoother than the swift. I didn't like the faff of folding the airnimal twice a day for my commute and wanted to get my swift back on the road. I was happy to find out that the 520 rear wheel would fit the swift without any mods and that the crown to axle length on the airnimal forks was exactly the same as on the swift. I needed new forks anyway.