A motorcycle suspension system, like suspension systems on all other vehicle types, performs the primary job of absorbing the rough surfaces beneath the machine’s tyres and isolating the rider from the resultant jolts. In addition to enhancing the comfort for the rider, however, a motorcycle’s suspension plays a key role in defining its handling and steering characteristics. Based on its setup, a motorcycle suspension can play an important role in enhancing a motorcycle’s grip and stability in a straight line, as well as around corners. Now, while it’s natural for us to imagine a motorcycle’s front suspension setup as a twin telescopic unit, there are other varieties too which aren’t as common. Through their rich history, motorcycles have seen a whole bunch of suspension setups being tried upon their front end, while some were effective, others weren’t, and a few others were just too expensive and complicated. In this article, we will discuss all the major varieties of front motorcycle suspensions, their workings and respective characteristics.
These are the most commonplace front suspension systems, and an overwhelming majority of motorcycles the world over uses this system. A telescopic forks assembly comprises of a pair of fork tubes which are attached to the motorcycle steering system, that is, the head bearings via a triple clamp, or yoke. These fork tubes go inside a pair of sliders, which are attached to the front wheel spindle. This entire assembly has springs inside, along with fork oil creating an effective shock absorbing system.
Upside down telescopic forks
A more modern version of the conventional telescopic fork suspension is the upside-down forks, where the sliders, which typically are at the bottom, are positioned at the top. The sliders also contain the spring as well as the oil. The upside down or USD fork offers advantages in terms of lesser un-sprung mass, and a stronger, wider slider clamping on to the yoke. While it offers more stability and is suited for performance oriented machines, if the oil seals inside the top part break, the oil would drain out and it won’t be usable unlike the conventional forks where the system still remains functional for some time after leakages.
Modern telescopic fork suspensions come with a lot of adjustability in terms of pre-load, as well as damping. The telescopic fork setup on expensive motorcycles allows for spring pre-load, so as to stiffen up the suspension and make for a tauter ride for better control. In addition to pre-load, damping can also be controlled by regulating the oil flow within the forks. Suspension damping on more advanced systems facilitates stiffer damping when overcoming small bumps, and softer damping as the bumps get bigger, applying more force on the springs. The damping can be controlled for compression as well as rebound.
An improvement over the conventional forks, the Saxon-Motodd suspension comprised of a single wishbone that connects the frame with the twin telescopic sliders, at a point just above the wheel. There’s also a shock absorber located on the wishbone, which does the job of handling most of the suspension and braking forces. Among the system’s advantages are a lower un-sprung mass and decoupling the steering function of forks from shock absorption. This also reduces dive under braking and is said to enhance stability and comfort.
While there are more effective suspension systems as compared to telescopic forks, they are also more complex, expensive to produce and not as durable. The telescopic forks, owing their relatively simple design, low cost, light weight and visual symmetry are adopted almost universally. Early telescopic front forks were un-damped, and have their origins as early as 1908, with damped front forks coming into existence by the year 1935.
The Hossack front suspension did a great job of separating the suspension from the steering. The system also significantly reduced the minor reduction in wheelbase that motorcycles suffer under heavy braking. The system comprises of 2 wish-bones, along with an upright as well as linkages for the steering function.
Trailing Link front suspension
A trailing link or trailing arm suspension setup comprises one or more arms, or links, connected between the axle and pivot point. The pivot point is ahead of the axle, and the link trails that point, hence the term trailing arm.
Leading link front suspension
Leading link, or leading arm suspension is somewhat opposite of the trailing link suspension. In this type of setup, the wheel is suspended ahead of the pivot point through a link. Since the link leads the pivot point in this case, it’s called a leading link suspension.
Girder front fork setup was used in some of the earliest motorcycles. Typically, a girder fork setup would comprise of a pair of upright legs, which are connected to the triple clamps. The pivot points on the legs are short links, which are connected with the triple clamps with a spring generally placed between the top and bottom triple clamps.
While in the first look some may mistake the Springer leading link fork with a Girder, it’s actually different. Unlike the Girder, which has its leg fixed into the wheel, Springer fork has two parallel legs. The rear leg of the set-up is fixed with the bottom triple clamp, and the leading link goes into the wheel hub, while also holding the other, parallel leg which compresses the spring, which is turn is usually mounted on the triple clamp, and compresses against the top triple clamp.
Hub-mounted steering and suspension
Hub-mounted steering systems for motorcycles are used very rarely, though they have been used on some production motorcycles. The system utilizes one or more swing arms connecting the main chassis with the front wheel, which allows for the vertical movement of the wheel. The steering points of the pivot for a hub-centred motorcycle are located in the hub unlike a conventional telescopic fork equipped motorcycle, which has it in the headstock. The braking forces can be channelled horizontally through the swing-arm without having any impact on the suspension. The hub-centred steering and suspension system is claimed to offer great agility and consistency of steering, which is better than conventional forks. The efficacy of the system in the real world, however, is still a bit contentious. With its complex set of linkages and complicated setup, the hub-centred steering and suspension system is also quite expensive to produce. Another issue reported with such systems is a relative lack of feel and feedback to the rider while steering the motorcycle.
There are a few other sub-divisions of the front suspension system as well, although the systems mentioned above broadly cover all the major front suspension types for a motorcycle. We’ll come up with a similar article for the rear suspension systems for motorcycles as well. In the meantime, do share this article with your friends who you think would be interested in learning about the motorcycle suspension systems discussed here. Do not forget to tag us on your favourite social networks if you liked the piece. You can also let us know your thoughts and opinions through the comments section below.