Cryptic crossword clue
A drug-taking bicyclist is transforming ease of comprehension 13

The most common and most likely answer to this crossword clue is the 13 letter word ACCESSIBILITY

I've seen this crossword clue in The Guardian
A
C
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Buddy explains!

The straight part
We know that "ease of comprehension" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case ease of comprehension = accessibility.
The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.
This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.

What does ACCESSIBILITY mean?

ACCESSIBILITY noun
  1. The quality of being accessible, or of admitting approach; receptiveness.
  2. Features that increase software usability for users with certain impairments.

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