why i was telling to replace tyres at delivery is because at that time you will get a price slightly less than the market price of your cars tyres. if you wait for few months, they may go for less than half of that price. both of these may not be really required. underbody coating maybe useful to some extent. let me tell you something about Teflon. Any company other than DuPont, offering anything with the name of Teflon is cheating in some way or the other. "Teflon® is a registered trademark and a brand name owned by DuPont, and is used on a range of products. Teflon® is not a specific chemical or product name. The Teflon® brand represents a family of high-performance products that are used in a wide variety of industrial applications and consumer applications. The Teflon® brand has come to represent a variety of benefits to consumers including easy clean, nonstick, repellency and durablity." source: What is Teflon®?