Upside Down Telescopic Forks: Advantages And Disadvantages

If you are a motorcycle enthusiast, you would always want your machine to handle well. A more stable motorcycle in a straight line and sorted around bends is desirable for the avid rider. The motorcycle’s suspension plays a vital role in fulfilling that objective. While the rear suspension of a motorcycle only has to absorb the undulations, the front suspension has to carry out the additional responsibilities of steering and absorbing the tremendous stress harsh braking puts it through. Thus, the front suspension has a pivotal role in handling a motorcycle, especially under extreme conditions. Most modern motorcycles come equipped with a telescopic fork suspension set-up, which has been doing this duty on two-wheelers since the late 1930s. The usual ‘right side up’ telescopic forks have proven their utility for most street-based motorcycles, and they work exceptionally well. However, engineers figured that the traditional telescopic forks had scope for improvement on the racetrack, where even the slightest technological advantage can make a big difference. In the late 1980s, motorcycle racing teams gathered that turning a telescopic fork suspension upside down or ‘inverting’ offers some advantages, especially under extreme conditions.

The majority of the racing motorcycles have now adopted the upside-down configuration. Most high-performance street motorcycles also come equipped with inverted or upside-down forks these days. But are these upside-down forks any better than their traditional ‘right side up’ counterparts? If yes, what are the technicalities which make them superior? Are the advantages offered by upside-down forks relevant only for extreme use or even in everyday conditions? In this article, we will find the answers to all of these questions.

What really is the advantage of a USD fork?

To start with, some believe that the advantages of an upside-down fork set-up are many, including more rigidity, reduced sprung and un-sprung mass, better stability and position for brake caliper mounting, and reduced friction between the stanchion and slider. While some or all of the above advantages may be true, it depends upon various other factors, including the design, construction, materials used and specifics of the suspension in question. However, the one clear, undeniable advantage of upside-down forks is that they offer a more rigid set-up overall, which has a better capability of handling extreme stress during hard steering, braking, and other strenuous conditions. Why is that so?

To fully understand an inverted fork telescopic suspension’s advantages, we first need to know about the construction of a standard telescopic fork suspension. A telescopic fork suspension comprises an outer slider wider in diameter and is generally quite sturdy. The other part of the telescopic suspension is the stanchion which moves inside the slider. Within this set-up, you also have springs, dampers and oil seals which prevent the damping fluid from coming out of the assembly. While the spring compresses and expands to absorb and release the energy transferred to the suspension as the wheel passes over rough surfaces, the damper unit controls the spring’s compression and expansion rate. Therefore, modern telescopic forks, whether right side up or upside-down, utilise a similar spring and damper set-up. Hence, in terms of the operation of the spring and dampers, there is hardly any difference between the conventional telescopic forks and upside-down forks. There is, however, a big difference in the strength and rigidity of the two set-ups. A telescopic fork experiences the most amount of stress just below the bottom yoke, or what is also known as a triple clamp or fork bridge.  When a motorcycle is subjected to heavy braking or cornering at high speeds, it’s this part of the bike, right under the triple clamp, subjected to the most stress. If the steering componentry is not rigid enough, it will make the steering and suspension bend and flex, which is not good for dynamic ability, steering feedback or rider confidence.

In the traditional, right side up telescopic fork set-up, it is the less rigid stanchion that has to bear all the stress. In an upside-down fork set-up, the roles get reversed, and the slider, which has a wider diameter and is sturdier, gets to handle most of the stress. With the stiffer slider taking over that duty, the torsional stiffness of the suspension is increased, preventing flex, or bending. This leads to improved rigidity, enhancing stability and rider feedback, especially under extreme conditions where the mechanicals of the motorcycle are subjected to extremes. Also, while it’s not always the case, the sliders on an upside-down fork suspension are often longer than the ones on conventional forks. This increases the overlap of the slider and stanchion, resulting in an overall sturdier set-up. In a nutshell, in the case of upside-down forks, with the more rigid slider taking up the responsibility of absorbing the lion’s share of stress, the flex is reduced – improving handling and feel.

The benefits offered by upside-down forks over their conventional counterparts are generally not very noticeable during street use. Even the conventional telescopic forks on motorcycles from reputable manufacturers are exceptionally well designed for the purpose they are meant for. It would be challenging for the riders to figure a difference between the two in everyday road conditions, or even while pushing the bike around moderately challenging situations, like while canyon carving. In extreme conditions, however, such as on a racetrack or in specialised applications such as a motocross bike, the advantages offered by inverted forks are more evident.

Are there any downsides to upside-down forks too?

Gravity is the biggest enemy of upside-down forks, especially with a worn out or damaged oil seal. The oil reservoir is like an upright vessel in a conventional telescopic fork suspension. So even if the oil seals are broken, the oil leaks out gradually, as gravity tends to pull it back into the reservoir. However, in the case of upside-down forks, the oil reservoir is like an inverted vessel. Hence, if there is a cut or leak in the oil seals, the oil tends to seep out of the reservoir onto the stanchions rather quickly. With the accelerated flow of the leaking oil, there is a chance of the slippery oil spilling over to tyres and front brake discs, which can be potentially hazardous. This is not a common occurrence, though, as upside-down forks come with extremely sturdy oil seals that last really long. It is, however, advisable to take care of the overlapping surfaces of a telescopic fork, especially the stanchion, by cleaning it regularly and keeping it clear of any dust, grime and other debris. Fork boots or gaiters can go a long way in keeping such undesired elements away, thus enhancing the life of the oil seals and suspension.

Another disadvantage of upside-down forks is that they are generally more expensive to make, which means that motorcycles which come equipped with them are slightly more expensive. If you are not going to put your motorcycle through the stresses that an upside-down fork is meant for, it will amount to extra money spent on the equipment you won’t be able to utilise. Aesthetically, however, upside-down forks generally look cooler and meatier than their conventional alternatives, so that’s definitely a value add. However, both types of suspension work very well for most street-based applications.

Upside-down forks are a superior design over their conventional telescopic fork counterparts. Whether or not you should opt for upside-down forks depends on whether you would be able to put the additional sturdiness offered by the inverted suspension units to use.