For a belt drive with driver pulley diameter 150 mm and driven pulley diameter 75 mm, center distance 0.80 m, determine the speed ratio and whether the belt length should be adjusted.

• A. Speed ratio = 2:1; belt length remains unchanged and no re-tensioning is required.
• B. Speed ratio = 1:2; belt length should be lengthened automatically.
• C. Speed ratio = 2:1; belt length is predicted; re-tension is only needed if belt length mismatches.
• D. Speed ratio = 2:1; belt length should be recalculated and re-tensioned if necessary.

Answer: (D)