I know that plosive consonants can change in natural Mandarin speech, like intervocalic g is almost always elided, and sometimes k, but b and p are almost never elided, but when should d be elided?
I found this example of 知道 as zhao/zao, (https://chinesehacks.com/vocabulary/syllable-contractions/),but I'm trying to focus on Beijing Mandarin instead of Taiwanese so I didn't think much of it. However, I then found this page on the Beijing dialect which had the same change (https://pinyin.sogou.com/zimeiti/article/1255).
The often cited example is that 知道 changes to rdao in 不知道 for Beijing speakers, but when should d disappear and remain then? Is it something about dao being unstressed in 知道 but stressed in 不知道? Is it about the combination of zh+d? or i+d?
Any insight would be appreciated.