How do I know if I need an endurance bike versus a race bike?

If you experience neck, shoulder, or lower back pain on rides longer than 2 hours; if you cannot comfortably reach the handlebars in the drops; if you ride primarily for fitness and enjoyment rather than competition; or if your roads are less than perfectly smooth, an endurance bike is the right choice. Race bikes are for riders who can comfortably maintain an aggressive position for hours, prioritize marginal speed gains, and ride primarily on smooth roads. When in doubt, choose endurance — you can always lower the stem and add a longer stem to make it more aggressive, but you cannot make a race bike as comfortable as an endurance bike.