My rear wheel is original: 9.5mm axle, 28 holes hub, narrow single wall rim with 20x1.75 tire. In the future, I plan to upgrade to a 10mm axle, 36 holes hub, wider (22-24mm) double wall rim with 20x2.00 tire (like schwalbe big apple). I think it will ensure longevity and add comfort. Also will add more weight.