What is the key to the bike frame rack size

 Actually the frame size usually refers to the bottom bracket (axial and the location of the foot) is to install center to the front of the frame on the triangle tube electric contact center height. 

Domestic mountain bike generally use two standard, a European standard, bike frame,one is the standard in Asia. 

Asia in the standard are: 15.5 -inch 17 inches (19 inches ) In the European standard: 16 inches 18 inches, 20 inches 

There are special small soft tail frame, 14.5 inches to standard. 

The above refers to the mountain. Road bike frame size is also refers to the size of the same place, generally speaking, there are these standards. 430, 465, 500, etc .Frame according to your height is best choice, to try to ride a car shop is a recommended practice.