Mtbforks - Mountain Bike Zen
Types of Fork
Forks can be rigid or have suspension. Most modern mountain bikes will have suspension forks to absorb the impacts of riding over rough terrain, this isn't just about comfort as it can reduce musculo-skeletal injuries as well. Suspension forks can have fixed or adjustable travel, this is how far they will move up and down to absorb impacts. The greater the impacts you are likely to experience the more travel you will require. Downhill riders and particularly jump riders will need the most travel, cross country and trail riding will not need as much travel, concentrating on good quality suspension rather the travel distance is more important here.
As well as offering adjustable travel, more expensive forks can also offer adjustable rebound and lockout. Rebound refers to the speed with which the forks will bounce back following an impact. If this is too soon the ride will be very bouncy and steering will be difficult, if it is too slow then the forks will not recover their position before the next impact which will reduce their effectiveness in dampening the bumps.
Lockout, often shortened to LO, will offer the option of switching off the suspension, although this usually allows a little movement rather than total lockout. This is useful for climbing hills where the front suspension can add to the effort required to get up steep terrain by absorbing some of the climbing energy you are putting into the climb rather than all of your efforts being transferred to your tyre traction. Lockout can be via a turn key on the top of one of the side of the fork or via a remote switch which can be mounted on your steering bars. A remote switch is useful if you want to switch the suspension off and on without needing to stop riding, it is almost impossible and a little dangerous to try and switch a turn key suspension on and off while riding.
Forks can also be air sprung or coil sprung. Air sprung forks will fail very quickly if an air leak develops but they usually provide a little more control over the firmness of travel, they will often have a coil as well for rebound control. By contrast coil forks are usually a little cheaper and more easily maintained will great options for controlling travel, lockout etc. the main disadvantage with a coil fork is weight, they are heavier than air sprung forks. The other disadvantage is that you may need to replace the spring for less or more stiffness as they are generally aimed at the 'average' rider and if you are much heavier or lighter than the average your fork will not suit you well.
Replacing Forks
If you have suspension forks, use your bike often, and own it for long enough, it is inevitable that you will need to replace your forks at some point. Before you do you need to know whether your forks are threaded or unthreaded, whether you want QR or quick release forks for quick release wheels or bolt through forks, what size steerer tube will fit the head tube of your bike frame, how much travel your bike is intended to be used with - frames are designed with specific trigonometry depending on intended useage - a bike intended for 80mm forks may not be well suited or even safe with forks that have 180mm of travel. The longer the travel of the forks the higher off the ground they will raise the bars which will also effect how short you will want to cut your steerer tube.
Replacing your forks is fairly straightforward, the trickiest bit is cutting down the steerer tube, make sure you measure this several times before cutting, sometimes it is a good idea to measure, leave it for a while and then measure it again, once cut it you can't put any length back on and shortening the length by small amounts can also be quite tricky.
Once you are ready to cut you need to make sure your blade will be straight. A hacksaw will usually be sufficient but to keep it in a line. Ideally a steering tube guide clamp would do the trick but most of us don't have, it is possible to improvide with a workbench clamp, old spacer rings, or even an old hoover tube. The aim is to make sure you cut straight across the tube. A little wobble wont matter much but a cut at a bad angle could ruin your whole project. If in doubt take it to your local bike shop and have them sort it for you.
Once you have cut down the tube you need to smooth off the edges to avoid cuts and damage to your other equipment. A good coarse sandpaper will do the job well enough but a rasp or metal file would be best.
Once the tube is cut to length you will need to ensure you have a star nut inside to screw the top bolt through. Again this is best done with a specialist tool - a star fangled nut setter - again most of don't have one of these so the end of a screw driver, a socket wrench extension arm, a wine cork, of any other array of improvised tools can be used. The two most important things here are - make sure you do not set the nut too far down the tube - around 15mm is a good depth, if you go too far you will have to try knocking the nut all the way through the tube - not easy, or use another but.
While knocking the nut down you also need to make sure it remains true to the line of the fork tube so your bolt will screw in properly. Using a small coin or washer can help ensure the blows are evenly spread. Fairly gentle tapping is best for control to ensure you don't muck this up.
Finally just refit the headset and stem onto the fork and screw in your top cap.
Servicing Your Forks
You are best off having your forks serviced by the manufacturer or your local bike repair shop, doing it yourself will probably void any warrantee
If you have no warranty or are feeling confident then you can do this yourself. The best thing to do is find a manual for your fork which will usually explain in full the servicing procedure.