I purchased 2 of the thule 501s for both of my mountain bikes (with different size tires). The install was fast and easy and most of all, no tire removal. The ratchet locking arm and hook arm holds the bike in place. It's an awesome well designed pickup in-bed rack!
This is an awesome bike rack system for pickups. Quick and easy, best of all you don't have to remove the front tire. I purchased 2 501's and they work great with both mountain bikes (of different size tires and frames).