Do I need a base layer under an aero race jersey?

It's optional but recommended in most conditions. A thin, sleeveless mesh base layer improves moisture management and can actually enhance the aero jersey's fit by providing a smooth surface against your skin. In hot weather, a base layer prevents the jersey from sticking to sweaty skin and makes it easier to remove. In cooler conditions, a lightweight merino or synthetic base layer adds warmth without significantly affecting the aero fit. Avoid thick base layers — they'll make the jersey too tight and restrict breathing. If your aero jersey is already at the limit of comfortable tightness, skip the base layer.