Final answer:
The proper trailer height when coupling with a converter dolly is slightly lower than the center of the fifth wheel, to ensure a secure locking without damage as the trailer is lifted during the coupling process.
Step-by-step explanation:
When preparing to couple a rear trailer to a converter dolly, the trailer height should be slightly lower than the center of the fifth wheel.
This ensures that when the trailer is backed up, the trailer's kingpin will slide into the fifth wheel and be locked securely without causing damage. Having the trailer slightly lower than the fifth wheel ensures that as the trailer is lifted during coupling, the weight is evenly distributed and a proper connection is made.