Performance evaluation method for elastic material

A method for producing or designing a tire, the method comprising:

• a step of applying a strain to a test piece made of an elastic material to form at least one low-density portion inside the test piece;
• after forming the at least one low-density portion, a step of obtaining projected images of the test piece by irradiating the test piece with X-rays at a predetermined first time and at a second time after the first time;
• a step of inputting the projected images of the test piece into a storage unit of a computer having a central processing unit;
• a step of identifying the at least one low-density portion based on the projected images, wherein
• the central processing unit executes:
• a step of identifying the at least one low-density portion based on the projected images at the first time;
• a step of identifying the at least one low-density portion based on the projected images at the second time;
• and
• a step of identifying a volume change as a ratio Vt/V0 between a volume V0 of the at least one low-density portion at the first time and a volume Vt of the at least one low-density portion at the second time, as the volume change;
• a step of obtaining the elastic material which satisfies that the ratio Vt/V0 is equal to or less than a second threshold value;
• and
• a step of producing or designing a tire by using the elastic material.