The blending of the radii around the rim makes up the rim contour. See below. The Rim Contour starts at r02 on the outside of the mouthpiece and ends at r2 at the start of the cup.
Hint! Use manufacturer's descriptions and comparison charts as a very general guide and starting point.
Only GR Playing Tests will be the definitive method to determine proper match between player, mouthpiece, and instrument.
Rims are usually classified into four very general categories:
May feel very comfortable and aid endurance, but may make flexibilities a challenge. Wider rims have an anchoring effect and may aid in distribution of mouthpiece pressure in the upper register. Usually if a rim is too flat or too wide it will impinge lip vibration and cause a thin sound.
May aid flexibilities and attacks, but may be uncomfortable to some players. Too narrow a rim could have a "cookie cutter" feel if a player uses too much mouthpiece pressure, but to some, will give great flexibility and precise attacks. If a rim is too narrow or to sharp is will hurt endurance or cutting could occur.
The larger rim area of the flat rim will aid endurance and have an "anchoring" effect, perhaps at the expense of lip flexibility. Some players will greatly benefit from the comfortable feel and anchor of a flatter rim. Usually if a rim is too flat or too wide it will impinge lip vibration and cause a thin sound.
Round rims have a very secure feel and may aid flexibilities, but may hinder endurance. The reason for this is that with a rounder rim, there is less effective rim area contacting the chops. This is a similar situation to the narrower rim, however, some will excel with a rounder rim.
The rim contour is made up of small arcs or radiuses. The three that make the most impact are:
1) Inside or Bite Radius-Rb
A smaller radius will give the rim a sharper feel. This will aid attacks, but too sharp a bite may be uncomfortable. A larger radius will have a softer bite. This may feel very comfortable to some players, but may make clean attacks more of a challenge. A softer bite may also make the cup feel slightly wider.
2) Crown Radius-Rc
This radius determines the roundness or flatness of the rim. This may also be referred to as the "high point" of the rim. The high point (r0) will also determine the feel of the diameter of the cup. If two cup diameters are the same, the mouthpiece with the high point closer to the outside may feel larger.
3) Outside Radius-Ro
This will determine how wide the rim feels on your chops. A smaller outside radius will make a narrow rim feel wider, especially in the upper register, where more mouthpiece pressure is experienced. This will give you more rim area on your chops if you add mouthpiece pressure.
The plating on the rim will also affect player comfort and resonse!
Whether you choose Silver, Gold, Rhodium, Lexan, or Delrin Plastic, each will have a different grip!