The only bike rack that fits any vehicle, any bike, and is actually small and light enough to attach below your saddle
TrunkMonkey is an inflatable rack not unlike the HandiRack but for your two wheeler, not skis. It’s made of an ultrasonically welded polyvinyl core surrounded by a rugged Cordura Kevlar outer shell and inflates in two minutes using the included air pump, attaching to any vehicle with a rear trunk or hatch opening. And when you’re done, just deflate it using the pump, pack it in its carry case, and throw it in your trunk, until next time. TrunkMonkey sells for US$100 – check out their Kickstarter page.