What are the key factors to consider when choosing a car rack for a gravel bike, and how do you balance the trade-offs between ease of use, bike security, and vehicle compatibility? For example, should I prioritize a rack that is specifically designed for gravel bikes, or can I get away with a more general-purpose rack? Are there any specific features, such as wheel trays or fork mounts, that are essential for gravel bikes? How do I determine the correct size and fit for my bike, and what are the implications of choosing a rack that is too small or too large? Additionally, what are the pros and cons of different types of car racks, such as hitch-mounted, roof-mounted, and trunk-mounted racks, and how do they impact the overall user experience?