First thing’s first – let’s see how momentum passes from the wheel to the shock of the frame.
From the start, we know that the rear shock of a frame is nothing but a system of levers that act upon a resort that absorbs shocks. An important aspect is that the system of levers, known as linkage, work differently compared to the shock according to the position of the rear wheel axle. Almost every manufacturer conceived its own working system of the rear shock and emphasised different properties that improved, in their vision, the riding. However, things went hectic and expect to come upon tons of designs and information when looking for a good product. So, sometimes the problem is that information doesn’t reach us in order to actually influence our choice in terms of which bike we’ll buy.
Keeping stable is the main reason why vehicles have suspension systems. Sensitivity is provided by the capacity of the suspension fork and the rear shock to take in the bumps the wheels cross over. Most suspensions are highly unsensitive in the first interval of their travel. This simply means that a bigger applied force is needed to compress the resort in the first phase. You can notice a low-quality fork by the latter property and by the fact that sensitivity to bumps lacks all the way through and the end of travel is reached quite easily. All these make up a poor suspension system, that doesn’t work for little obstacles and thus puts stability in peril (helping crahes occur).
Liniar and progression? Opinions vary a lot in this regard. One thing is certain though – all riders want the first length of the travel to respond right away to the shape of the trail they cover and by the time heavier stuff kicks in, the full length of the travel to become difficult to reach, like a progression – the closer you get to the end, the more compression is needed. For all these, manufacturers found solutions, and most of them are featured on high-end products – spacers that reduce the volume of air or a negative inner chamber of large volume.
For instance, a system of levers that on the latter part of the travel becomes linear would need a smaller volume of compressed air, where as another would require a larger volume in order to compensate.
What you must make out of the information depicted above is that the shock is an element that needs to be in harmony with the linkage system. This translates in the fact that compression and rebound are set by the manufacturer accordingly to the frame’s features. That is the reason why high-end shocks have written on them the tune-up of the compression, known as valving.
How a shock behaves is dictated by where the piston finds itself along the travel, where as a system of levers moves freely between its limits without meeting any resistance. This is the explanation for why a shock absorbing system is needed. Its action controls the behaviour of the lever system and offer stability during riding by responding accordingly to the bumps encountered.
Another vital chapter lies in the way the suspension acts at the middle of the travel, or in the midstroke level. This is the position in which both shock and frame are most active. Almost all shocks, more or less, have a compression and rebound speed limited by the manufacturer insomuch as not to influence the sensitivity with which it responds to trail variations.
The frame joints and their influence over shock performance
When you switched from a hardtail to a full-suspension bike, you might have noticed that all the pivoting points of the frame feature rotational elements, mostly in the form of bearings.
All the forces met by the encounter of the bike with the ground pass from tire to rim, from spokes to hubs and so on until they reach the shock. Performance can be reduced by a poor rotational element in the joints.
Why are bearing preferable? Simply put, it provides less friction. This happens because the balls inside are constantly moving and the friction pattern is actually an ever-moving dot-like print.
Most manufacturers use bearings, but there are some cases when they use nuts, which pivot less, and that kind of opening is supposed not to inflict too much friction or, at least, a negligible amount. However, the more friction there is, the less responsive the shock becomes.
Anti-squat and pedal kickback
When searching for the shock of your dreams, you will definitely stumble upon these terms.
Antisquat depicts the amount of opposition the the linkage system generates when it finds itself under the pressure of the chain. Put on short, the harder you press the pedals, the less responsive the shock becomes.
If, for instance, a frame features a high level of antisquat, then you will experience poor performance of the shock when pedalling with great power. However, this is not necessarily a bad thing, since it provides advantages (stiffness) while climbing.
As opposed, if the antisquat factor is low, the frame shock is hyperactive and leads to the other extreme, known as pedal kickback. What this means is that the shock is so sensitive, that every push of the pedal is firstly taken in by the shock, and only afterwards (and what is left, of course), by the drivetrain. This generates a rocking motion as well. In order to prevent this from occurring, most bikes feature the ProPedal and Lock-out systems.
By now you probably realised that the bike that has good features for both climbing and descending doesn’t exist. The model you decide to purchase should be in accordance with your riding style and your intended usage. Still, we have our own darling in terms of rear shocks, and that would be Yeti’s SwitchLink.