Wild Cherry: The thinner the insert the more air gap you get. I can't answer your question on how it works or why because I just don't know. I used the HPI inserts in the Sorex tires when I was in California at nationals because that's all they had. The tires felt pretty full. I don't know for sure if a thinner insert in the tire would have helped me but my car sucked that weekend. More companies are making thin and extra thin inserts now i.e. Sorex, Yokomo. Since I left that race in California 3 years ago I haven't used another HPI insert. I don't want to have flashbacks. For at least two years now I have been using the yok ZR-037F(less gap) and ZR-039F(more gap) with the Sorex 32 or 36(depending on track temp). That is what works for me. By no means is my car glued to the track and does spin out from time to time. So don't expect a miracle with them. If you want a car that's glued to the track slap on some Cyan and Magenta's and go run on some carpet.