Suspension forks are almost universal on mountain bikes these days, but just leaving them there as they came is a waste of their potential. After all, you wouldn’t leave the saddle the height the same if it didn’t fit would you?
The amount of tuning changes you can make depends entirely on the fork you’ve got, but we’re going to cover the essentials first. We covered spring rate last week so now its time to look at controlling that spring properly with damping adjustments. Then we’ll move on to internal adjustments and servicing later in the month.
Anyway – enough with the intro and let’s take the second of 3 steps to suspension fork heaven.What is damping?
Damping is the process that turns your spring into a useable shock absorber by slowing down the fork on impact (compression damping) or on its return (rebound damping). In most forks this is achieved by pushing oil through a small hole (valve) although some super cheap forks rely entirely on friction. By adjusting the size of the hole (valve aperture) you can adjust the speed oil can push through and therefore, the speed your fork can compress or extend. More advanced forks use springy discs (shims) that act like a leaf spring, bending out of the way with big hits to allow more oil through (speed sensitive damping) or provide an emergency bypass route for oil (blow off circuit).
If we’re starting to scare you now don’t worry, all you have to concern yourself with for now are the adjusting knobs on the outside of the fork.
First consult your manual, as different forks have their adjusters in different places. Pace, Fox and most Marzocchi forks have both rebound and compression damping adjusters at the top of the fork (on the same or different legs depending on model). Rock Shox and Manitou tend to have compression damping at the top of the leg, and rebound damping at the bottom of the leg. If you’re wondering why damping is normally on the right hand side, it’s to keep it away from the heat generated by the disc brake, which can make oil (and therefore damping) faster moving if it gets really hot.
So that’s the what and where, but what about the how?Rebound damping
Without rebound damping your fork will fire back out from an impact as fast as it compressed, throwing your front wheel in the air and you into a bush. However with too much rebound damping, the fork won’t return to it’s starting point before the next hit. If you then show it a set of steps or braking bumps, it will just ‘pack down’ until you’ve got no suspension left at all. The happy medium will move fast enough to keep the front wheel ready for any impact but keep the front wheel on the ground all the time for maximum cornering traction.
With a bit of experience you can get an idea of rebound speed just by pushing the fork up and down. Unfortunately it’s practically impossible to explain in words. It certainly shouldn’t come back so fast that it clunks on the top of the stroke or jumps your hands off the bar or wheel off the ground. There should definitely be a feeling of at least some control of the return speed. On the other hand you don’t want to have time to put the kettle on before it comes back up.
Trial and error isn’t easy when there’s so much to learn about riding your bike every time you go out, but it’s worth spending a bit of time dedicated to getting the fork just right for you. Find a bit of trail with bumps of different sizes (even a big kerb will do) and some repetitive bumps like routes or steps and ride it over and over again, changing the adjustment slightly each time. Formula One (ex Marin / Whyte) suspension expert Adrian Ward recommends lying a ladder on the ground and riding along the rungs over and over again, changing the adjustment until it’s as smooth as possible.
Once you’ve found your ideal adjustment then write down how many clicks or turns it is in the fork manual, so it’s easier to set up again if someone messes with it. Changing the spring rate of your fork will also mean changing the damping of the fork to cope with it. A stronger spring will generally need more rebound damping, while a softer spring will need the opposite.Compression damping
Simply put, compression damping slows the fork down gently to stop it slamming into the stops as soon as you it a big lump. However with too much compression damping, the fork can dive too slow or suddenly slow up (spike) leaving you to handle the impact not the spring. Ideally the fork should feel plush and responsive but never ‘bottom out’ hard, if you’re not even thinking about what the fork is doing you’ve probably got it smack on.
The repetitive riding and ladder tricks work just as well for setting compression damping. If the bottoms out repeatedly even with maximum compression damping then you need a stronger spring. If it never bottoms out even with minimum damping then you need a lighter spring.
Once you’ve found your ideal adjustment then write down how many clicks or turns it is in the fork manual, so it’s easier to set up again if someone messes with it. Changing the spring rate of your fork will also mean changing the damping of the fork to cope with it. A stronger spring will generally need less compression damping while a softer spring will need the opposite.
Beyond the basics
This suspension tuning series is designed to explain the basics to beginners. We don’t want to scare people by plunging them straight into oil changes, re-shimming valve stacks, position sensitive damping and adjustable blow-off damping just yet. Either be patient and we’ll get there soon, or go talk to the folks at TFTunedshox , CVI or Mojo, who make a living out of suspension tuning and have got far more experience and know how than we have.
Now you’ve got your dials where you want them how do you keep your fork working as well as when it was new? Next week, basic fork maintenance and cleaning.