120mm forks are also pretty popular in this category. XC bikes, especially 29ers, will still have the tried and true 4″ (100mm) of travel. Today’s bikes fall into three loose categories based in part on thegeometryfactors above, and also the amount of travel. Advances in frame design have allowed newer bikes to be set up with longer travel without the penalties of pedal bob and brake dive suffered by older models. Not too long ago 4″ of travel was the norm. “This bike has 9 inches of travel! More is better, right?” Traditionally, XC bikes had longer chainstays and wheelbases while all mountain and downhill geometries were much shorter, but that trend is changing lately with XC bikes getting the shorter chainstay treatment as well. A shorter wheelbase will allow for tighter turns, while a longer wheelbase can be more stable at high speed. Chainstay length also affects the overall wheelbase of the bike. Manuals and wheelies will be a cinch on a short chainstay bike, and more difficult when they are longer. A shorter chainstay will bring the rear wheel in closer to the center of the bike, and will make it easier to loft the front end over obstacles. In general, a longer chainstay will produce a bike that tracks well and wants to go in a straight line. These are the most common bikes on the LBS showroom floor and will have a head tube angle in the 67 to 70 range and relatively short chainstays. In between these two extremes is the All Mountain or Trail bike, which attempts to be a good climber while still descendingconfidently. At best the front wheel will wander and at worst the whole bike will “wheelie out” or flip over backwards. With angles in the mid 60’s, these bikes can handle super steep downhilltrail sections without the rider being pitched forward, and the front wheel strikes obstacles at an angle that allows the fork to absorb the impact and lets the wheel go up and over.As you might imagine, bikes with really slack angles tend to be terrible for riding uphill. At the extreme end of this design concept is the downhill bike. These bikes are fast andefficienton relatively non-technical trails with lots of climbing, but on really rough stuff and on downhill, the forward rider position and steeper fork angle can make an endo more likely.Ī “slack” geometry means that these angles are lower, which in effect moves the rider further back in relation to the center of the bike and the front wheel is further out in front. These steep angles will place the rider over the center of the bike for powerful,efficientpedaling, and the front wheel will tend to go in a straight line while climbing. The head tube angle on a bike like this will be in the range of 70 to 72 and the seat tube will be around 73 or more. Bikes intended for XC racing will have fairly steep head and seat tube angles (i.e.
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