On hot days, you normally default to shorts and a t-shirt. For hot days at the track, what’s the deal with the long pants and long sleeves?
Long pants and long sleeves provide as much, reasonable coverage as possible. The more skin coverage you have, the more protection there is for your skin. Even when driving on track in a non-competitive situation, dust, debris, fluids, glass, etc. are all very real possibilities. When pushing your vehicle’s capabilities, and doing this alongside other enthusiasts, there’s a lot of room for accidents. Of course the obvious concern is in an accident, even if minor, the possibility of cuts, scrapes, and burns from glass, plastic, fluids, etc. We know regular clothing isn’t going to stop everything, but having an additional layer before raw skin is better than nothing.
Most clubs/organizations require long pants, long sleeves, and close toed shoes. It is very common to also find requirements, or at least suggestions, to wear non-synthetic fabrics such as cotton. Some clubs/organizations are a bit more relaxed, allowing short sleeves, and sometimes even shorts as opposed to long pants. We always recommend verifying with your local club/organization.