Mountain bikesdiffer from other bikes primarily in that they incorporate features aimed at increasing durability and improving performance in rough terrain. Most modern mountain bikes have some kind ofsuspension, 26, 27.5 or 29 inch diameter tires, usually between 1.7 to 2.5inches in width, and a wider, flat or upwardly risinghandlebarthat allows a more upright riding position, giving the rider more control. They have a smaller, reinforcedframe, usually made of wide tubing. Tires usually have a pronouncedtread, and are mounted on rims which are stronger than those used on most non mountain bicycles. Compared to other bikes, mountain bikes also tend to more frequently usehydraulic disc brakes. They also tend to have lower ratiogearsto facilitate climbing steep hills and traversing obstacles.Pedalsvary from simpleplatformpedals, where the rider simply places the shoes on top of the pedals, toclipless, where the rider uses a specially equipped shoe with a sole that engages mechanically into the pedal.