Google has added a note to the product structured data help documentation explaining how to specify car markup while still being eligible for the Product review snippet feature.
What is new. The note says “currently Car is not supported automatically as a subtype of Product.” You “will need to include both Car and Product types if you would like to attach ratings to it and be eligible for the Search feature,” Google said.
Code example. Google then provided this example in JSON-LD:
Why we care. If you are only using car schema or product schema on your car and automobile landing pages, make sure to use both. If you don’t, review snippets for your site and web pages may not appear in Google search results.
Learn more from SEO and read A 12-Step Guide to Optimizing for Google Featured Snippets.