用英语表达“投诉自行车”可以有以下几种方式：
- Complain about a bicycle
- File a complaint against a bicycle
- Lodge a complaint regarding the bicycle
- Make a complaint about the bicycle
- Report a problem with the bicycle
根据具体的语境和目的，你可以选择最合适的表达方式。例如，如果你想要向商店或制造商反映自行车的质量问题，你可能会说：
“I would like to complain about the bicycle I purchased last week. The chain fell off, and the brakes do not work properly.”
或者，如果你是在填写一个官方投诉表格，你可能会使用：
“I am lodging a complaint regarding the bicycle I received, as it arrived with multiple defects and does not meet the product description.”