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 first essential – spring rate here. We’ll cover rebound damping, compression damping and more complex and advanced set up possibilities next week. Then we’ll move on to internal adjustments and servicing later in the month.
Anyway – enough with the intro and let’s take the first of 3 steps to suspension fork heaven.Spring rate
To get the most from your fork, you want it to give you its full travel but without flopping all over the place.
You also want them to have enough extension in them to keep your tyre in contact with uneven ground through corners.
The simplest way to set this level before riding is by measuring “sag”.
First measure the distance between crown and lower leg seal housing with nobody on the bike.
Then sit on the bike and measure the distance again to see how much the fork has compressed. This compression distance is the ‘sag’ of your fork.
Most XC forks are designed to work best with about 20- 25% sag, while some downhillers run forks at 35% while other XC racers will pump forks up to a barely moving 10% sag or less.
In this case we’re using a pair of Fox Float forks with 100mm of travel for general trail riding, so around 20 – 25mm sag is ideal.But what happens if the sag isn’t right?
Forks can either use an air spring or a metal or elastomer (essentially hi-tech micro cellular urethane blocks) spring. Each requires a different approach to tuning.
Air springs have the big advantage that they can be pressurised quickly and easily to cope with most rider weights and styles.
However, different forks run at wildly different pressures. Marzocchi’s low pressure forks run at 30psi or so (yet the Marathon runs a bodyweight psi negative spring) while Manitou’s can run around 150 psi or more so read the instruction manual for a likely starting point.
With coil or elastomer forks things aren’t quite as easy. Most will have some “preload” adjustment which pre crushes the spring, making it harder to move in the first place. The actual mechanical ‘weight’ or the size of impact / rider weight it can absorb is unchanged though. This means that if the spring stack is significantly too heavy or too soft you’ll have to buy / swap for a new one.
For this reason make sure you check ‘sag’ in a shop. At the very least check if you can slam the forks all the way to their stops too easily / only compress them a fraction. If that’s the case then ask the shop to change – or at least order replacement – heavier / lighter springs as necessary.Checking while riding
Once you’re out riding you’ll need to keep an eye on fork travel to tune it more exactly. Try using a thin zip tie around the stanchion (exposed section of upper leg) or just watching the filth tidemark on the leg to check whether you are getting full travel.
You should use all the available movement a couple of times a ride. If it’s happening more often than that or you bottom out with a thump at the end of the stroke, then you probably need to increase the spring rate.
Before the smart arses pipe up we’re covering compression damping later 😉
If you’re not getting full travel, then you need to reduce the spring weight till you do.
If your fork is equipped with protective boots, you won’t be able to see a grease mark or zip tie so you’ll just have to go by feel when you hit the big stuff.
Now we’ve got the basics of spring rate sorted, stay tuned to this channel and we’ll bring you a basic guide to the joys of rebound and compression damping next week.