A stumpjumper is a type of motorcycle that has been designed specifically for tackling deep mud and rough terrain. Having a bike that is built with a special purpose in mind offers numerous benefits. For example, these bikes can have a short seat tube, asymmetrical sidearms, and even a linkage-driven single pivot suspension system.
Short seat tubes
The Specialized Westwood Cycle is a venerable and iconic mountain Stumpjumper. With a long history dating back to 1981, it’s no surprise that Specialized continues to improve upon this icon. In the latest iteration, the company went to extreme lengths to reduce weight and keep the frame and suspension design streamlined.
Specialized engineers had the goal of building a lightweight mountain bike that was also a good performer. As such, they used FACT 11M carbon fibre for the new Stumpjumper project. This material is light and strong, but has a high stiffness. It also offers a large flex zone that enhances rebound and shock feel.
Pivotless seatstays/chainstays for a stumpjumper have several benefits. These include increased pedaling efficiency, reduced time in the stand for maintenance, and improved lateral chassis stiffness.
The design of a stumpjumper has evolved from a traditional Horst-link suspension layout to a linkage-driven single-pivot design. This allows Specialized to build the bike lighter, yet with the same ride quality of a carbon Stumpy.
In addition to eliminating the mechanical pivot, the new Stumpjumper features a flex zone in the seatstay that eliminates redundant material. It also has a slack head tube angle, a steep seat tube, and a low bottom bracket. Together, these changes make it easier to climb and more controllable in the corners.
The Specialized Stumpjumper is the first mass-produced mountain bike to be available. It was based on a bike that was custom built for the company’s founder, Mike Sinyard. In 1981, the bike became a big hit. Since then, the Stumpjumper has become a benchmark in its category. Today, it is available in three versions.
Asymmetrical sidearms have been a staple of Stumpjumper design. This design is a way of reducing the amount of kicks that occur on descents. They are also designed to enhance pedalling efficiency.
While the Stumpjumper has been around for 37 years, it has seen a few updates over the years. These include a new frame design, a better internal cable routing, a more durable and lightweight carbon frame, and improved shock sizing.
Linkage-driven single pivot suspension
Linkage-driven single pivot suspension is used on specialized stumpjumper bikes. These types of bikes are a cross between a four-bar and two-bar suspension design. They are designed to increase the progression of the leverage ratio and make pedaling more efficient.
There are several kinds of linkage-driven single pivot designs. The most common is the Horst-link design. This type of layout has a rear pivot located below the rear axle. It is a design that allows the suspension to move more freely over bumps when braking.
While most linkage-driven single pivot bikes have a regressive suspension rate, some have a progressive one. Some of these designs are harder to replicate with shocks. But they can offer decent pedaling characteristics and a less harsh ride than a conventional linkage-driven bike.
The Specialized Stumpjumper uses Fox DHX dampers, which are known for their light initial impact and responsiveness. In conjunction with the flexstays, the suspension is stiff enough for big hits, but also has enough low speed compression for smooth ride. A new digressive tune was developed by the engineers behind the Stumpjumper’s rear shock, resulting in a bike that pedals better and is more compliant to traction.
In addition to the big daddy of all Stumpjumper tunes, there are two smaller improvements to be found in the Specialized RX trail bike. One is the all-important digressive tune, which aims to provide just enough low-speed compression to keep your rear wheel spinning smoothly and efficiently. Another is a kinematics progression that flattens out as your travel increases. This is a boon for those riders who need more resistance to bottom out.
Hightower bikes are similar
Santa Cruz Hightower is a great all-round bike that is capable of handling everything from mellow riding to fast ripping. The LT model offers a few subtle changes that make it even more versatile.
One of the most notable changes is the new high-modulus carbon CC frame. It also features an internal cable routing, a threaded bottom bracket, and a tailgate shuttle guard. Another nifty feature is the Glovebox system. This feature is a little extra tool that has a latch that you can use to attach a jacket or tool wallet to the frame.
The bike’s rear suspension has a progressive lower-link VPP design to provide a more forgiving ride on gnarly trails. At the same time, the system is heavy and may give the impression of more movement uphill than the Stumpjumper’s shock.