What kind of content should racers create to attract tire company sponsorships?

Quality over quantity is key. Have separate social media channels for your race program distinct from your personal life - people who follow you because you race want to live vicariously through you and see elements that make you seem real and achievable. Most importantly, make sure you have usage rights for the content you provide partners, especially photography. Larger corporations have departments that need to approve every piece of content that goes out, so without proper usage rights, they can't use your content no matter how good it is.