The Space and Trek have different interior designs. Trek has removable wheels, and Space has non-removable wheels. Non-removable wheels are relatively stronger than removable wheels, but you will have to send the suitcase back to us for repair, which could take up to 45 days. Removable wheels are super easy to replace. If your luggage's wheels are damaged, we will send replacement wheels for free, and you should receive them in 3-5 business days. Additionally, the Space carry-on model has a slightly bigger capacity than the Trek Carry-on model.