09 Dec, 2016

Twiddling the 'Other Knobs'


In the previous two issues we dealt with the fundamentals of setting up your mountain bike’s suspension. Now we dive into the murky realm where adjustments are mostly subjective compression adjustments! – BY THE GENTLEMAN RACER

Believe it or not, there are forces that act on your bike’s suspension other than air pressure and rebound settings. On top of all this, we have the business-end of suspension, the damping or compression valving. Simply put, the right-hand side of your fork or the bobbins inside your rear shock’s shaft are nothing more than ingeniously-clever oil pumps. As your suspension moves, a volume of oil is manipulated by pistons, valves and shims, and the speeds at which this oil flows around the “damper” determines how the spring side of the fork/rear shock is controlled.

This can be a very complex and confusing thing to wrap one’s head around, but the basics of it are very simple. You just need to remember the following basics:

•   Compression adjustments are affected by two types of impacts, high-speed and low-speed compression.

•   A high-speed compression event generally happens when you strike a root or rock, always a short, sharp impact with a lot of energy.

•   Low-speed compression events usually refer to the rider’s weight  ‘squashing’ down the suspension of the bike.

•   Compression adjustments, although intrinsically linked to rebound adjustments, are a separate circuit, and changing one does not directly change the other. However, always bear in mind that the two work in unison to prevent you being pitched over the handlebars.


Expert Help

Thankfully, the manufacturers of these suspension pieces realised that not everyone is a Formula One engineer and most of us don’t need every adjustment under the sun. The majority of us ride cross-country, according to national sales figures, and most XC riders have a very simple set of suspension needs. We need a bike that pedals well (doesn’t slosh and dive around underneath us), has the ability to be firmed up to an almost ‘locked state’ for the long drags of district roads, and has easy access to the adjustments on-the-fly.

Most suspension is not even equipped with compression adjustment, save for a lockout lever or remote. Please be aware that modern suspension never locks out. There actually is no lockout. It’s just still called that to keep things simple, wink, wink.

Nowadays a lockout, whether activated by a manual lever or remote, only firms up the low-speed compression valving to the point of an almost rigid state. This allows the fork or rear shock to resist the temptation to ‘bob’ underneath you while still being able to react if you strike something while ‘locked-out.’

Each manufacturer employs very clever ways of dealing with this. Specialized employ the “Brain,” an inertia-valve that selectively opens or closes the valving depending on the severity of the impact. It can also have its sensitivity adjusted (Brain Fade). Meanwhile, Rockshox have used their “Floodgate” system for many years now, essentially a tap that only opens in an extreme circumstance or setting. The damper firms up completely until a threshold is reached, then excess oil pressure is bled back into the cartridge. And Fox have always had a “Back-door” system wherein a high-speed circuit feeds into a low-speed, along with a “blow-off system” to save it all from going bang in extremis.


Bottom Line

What all this means is that bike designers and suspension manufacturers work hand in hand to produce bikes that provide a stable-platform, with rider-selectable ‘lockout’ ability and subtle, small low-speed compression adjustment on certain models.

Fox attempted to simplify things further with their CTD damping system (Climb, Trail, Descend). They looked at the three modes of use we spend our time in and gave us suspension with three separate damping systems for each use, all adjustable manually or via a remote. Meanwhile, Rockshox use their adjustable floodgate to ‘tune’ the degree of movement allowed under lockout conditions, from barely perceptible to ‘wooden-frikkin-board,’ much like Specialized’s Brain Fade adjustment.


So, how does one use these tools? It depends on what you like, and these adjustments are completely up to you, the rider. There are no real rules, but there are a few recommendations:

1.If you have the adjustment available to change the firmness of the ‘lockout,’ use only as much as you absolutely need to prevent the bike from wallowing underneath you. The reasoning is that a suspension that is not too stiff is able to find more grip in loose, ragged corners and sketchy, steep climbs.

2.Always experiment until you find the sweet spot!


Until next time, keep the shiny side up!