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Speed you can feel.
If you think that your do-it-all triathlon speedsuit is all you need, well, think again. Castelli wind-tunnel tested the T1:Stealth Women's Short Sleeve Jersey against its own Free Tri suit, and found that the T1 provided an impressive three-minute advantage on a five-hour Ironman bike leg.
The secret is in the Velocity fabric, which provides a smooth surface that allows the air to rush past with no interference. Standard Velocity, which is stretchy, cool, and breathable, is used in the front of the T1, while textured panels of Velocity Mesh feature at the back and shoulder, where most air resistance occurs. Counterintuitively, the textured weave lets air pass by with less resistance, giving you a smoother and more aerodynamic profile when you're stretched out on the aerobars.
Castelli looked out for the details, too, such as an elastic waist with a silicone gripper elastic that keeps the T1 snugly sealed against your torso and a YKK Camlock zipper that stays where you open it, letting you pull in extra ventilation when you need to. Two side-entry back pocket provides enough room for food, tubes and even a light wind vest, so you can be prepared for inclement conditions without being slow and bulky.