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Triathlon bikes are specialized bikes (note the lowercase “s”) designed for use in either time trials or triathlons. Tri bikes (also called “aero” bikes) are designed to be ridden “against the lock,” meaning that the rider will not be riding in a pack (that would be violating race rules). Riders are typically riding at a fairly constant speed.

These bikes are designed to offer as little wind resistance as possible, and also allowing the rider to assume a riding position that is down low on the bars. Riders on tri bikes can often be spotted wearing aerodynamic helmets to further reduce drag.
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