3-Bolt Cleats
The majority of road cycling shoes feature a three bolt cleat design that has three holes on the bottom for installing the cleats. A 3-bolt cleat system will offer the highest stability rating and energy transfer. The cleat is larger in size and helps distribute the force of the rider's pedal stroke over a wider area of the pedals. This not only allows for a solid connection between shoe and petal, it also reduces pressure on the contact point greatly.
Popular Brands in 3-Bolt Cleat Systems: LOOK, TIME, SHIMANO (SPD-SL)
2-Bolt Cleats
A smaller percentage of road shoes feature a 2-bolt cleat design, similar to mountain clipless shoes. These shoes can offer a more comfortable option in a clipless system, and are popular with commuters and casual riders.
Popular Brands in 2-Bolt Cleat Systems: CrankBrothers, TIME, SHIMANO (SPD)