I just open both front and back car doors and have at it... usually I only change after races, and there's so much nudity at races, what's some more? If I want more privacy I just sit in the front seat of my car (Subaru Forester, so kinda roomy). Bibs can be hard to put on and off sitting down, so I'll just stand outside with a blanket wrapped around my waist. I stopped being modest a long time ago!