Two brackets with tire grooves design maximizes the stability. Please note for small size wheel bikes (smaller than 26"), the tire may touch one bracket (front) only. The bracket fits skinny road bike tire and mountain bike tire (max width: 2.5"). Reverse the holders' direction, so the bikes could be inserted from both sides if there is large space. Please watch the video in the listing. Could touch the chain or cassette. Could touch the disc rotor.