Originally Posted by dafydd
Probably won't work, there's roughly a 22 mm difference in brake reach. 20" fractionals are different from the 20" decimals. Plus you might want to check with BF about spacing, a lot of take-aparts and folders use narrower hub spacing.
Actually, the brake reach may not be a problem. I have successfully swapped many BMX wheels to the fractional sizes. It all depends on how accurately the brake bosses were welded on and what brakes are being used on the Bike Friday. The spacing and the hub design are indeed the biggest problems.