What is the difference between the Veloped 12er and the 14er?

The only difference between the models is the wheel size and the different textile kits. So you can, by buying another dimension of the wheel, rebuild the model to the other version.

The difference between the Veloped models is that they have different textiles. For example, the seat on the Tour model is 2" deeper (not wider), and it has insertions built into the seat cover, making it firmer and comfortable to sit on; it also comes with a rain cover for the seat and the basket. Performance-wise they are the same.