You must understand the vital parts of your bike, and know what to do in case any of the common problems covered occurs to you on the trail. Fixing a flat tire is probably the most common problem. I have seen as many as seven flats happen to one guy on a ride in the Sierras.
PROBLEM: BROKEN CHAIN
Problem: Your chain breaks on you while your ten miles from the car or the nearest bike shop......
Preventive steps: Check your chain periodically for tight links, twisted links, and most important of them all keep your chain oiled. Do this by rotating your cranks backward, if the chain has bad or stiff links they will catch and show up. Chains should be replaced after around forty to fifty hours of off road road riding depending on the circumstances. If you have a Shimano chain carry a Shimano chain pin. It is the only pin that will work with a Shimano chain.
Solution one: Carry a chain breaker in your tool pack. They are small enough to fit in any small area. Use the chain breaker to push the damaged pin out and re-connect your chain at the next sound link. Shortening the chain might make it difficult to ride in the big ring in front/big cog in rear, so ride with caution ...
Solution two: If you don't have a chain tool, you might have to improvise by using a fist size rock. Yes, it does sound primitive but effective if your ten miles away from anything. The best process for this method would be to place the back side of the loose link onto a similar sized rock then pound the pin in with the rock in your hand, if this works be very gentle riding back to your car. Replace the chain a.s.a.p.!
PROBLEM: LOOSE CRANK ARM
Problem: A loose crank arm will not only squeak and creek when you pedal, but it can also round off the taper inside the aluminum crank arm. If the taper gets rounded out, you will never get your crank arm to stay tight. It's history, recycle it. You can also loose the retaining nut or bolt that secures the crank arm down if your not careful.
Preventive steps: Check your bikes crank arms before every ride. It should be either a 14mm or 15mm wrench that you should have. This requires a special tapered wrench that sits into the crank arm around the nut or bolt. A socket works well also.
Solution one: A one-key crank bolt. A one key crank bolt is nothing more than an allen bolt that threads through a special cap and on into the end of the spindle. With a one key crank bolt, you can tighten your cranks with a 5mm allen wrench. Additionally, a one key crank bolt also works as a crank puller. Since the bolt is not flush to the crank arm it does require frequent tightening. Remember, keep the threads well greased for ease of tightening and loosening. (The new Shimano crank bolts use an allen wrench. Be careful with alloy crank bolts, use anti-seize to lubricate the threads, tighten with a steel bolt first and then the alloy bolt.)
Solution two: If you find your cranks loosening on the trail, and you don't have a 14mm crank wrench with you, improvise... Take the small crescent wrench out of your tool kit and try to use it to spin the bolt tighter. To facilitate getting the bolt tight, you might want to pound on the crank arm with a rock. The further you can get the crank arm onto the spindle the longer it will stay in place. If the arm falls off and you lose the bolt you will have to tap it back on with a rock, again, be very careful using such a primitive tool......
PROBLEM: LOOSE HEADSET
Problem: The headset of your bike holds the forks firmly in the frame. It also houses the bearings which allow for smooth and effortless steering. If the headset locknut comes loose, the first thing you should notice a rocking sensation in the bar and stem sometimes with a slight clicking sound. Riding with a loose headset can damage the bearing races and lead to potential fork failure.
Preventive steps: Check your headset before every ride. First straddle the bike and then grab a handful of the front brake, then rock the bike back and forth; if the headset is loose, you will have a light knocking feeling in the front end. This will require you to have two headset wrenches available (either 32, 36, or 40mm) and tighten the headset to the point where the rocking motion is gone but the front forks still turn easily without binding.
Solution one: Your best bet would be to carry compact emergency headset wrenches, They are available from a range of $5 to $10, and most of them can fit in your tool pouch. Another alternative would be to cut down one of the shop style headset wrenches so it would fit in your toolkit.
Solution two: Most riders don't carry headset wrenches with them on the trail. In that case, you will have to use your hands to cinch down your headset. Grab the top of the headset and twist the locknut clockwise. Wiggle the front end and repeat. You can't get a loose headset very tight with your hand, so you may have to stop and do the same process over and over again.
PROBLEM: TORN SIDEWALL
Problem: Your tires are made usually of a nylon belt, so they are prone to tearing. A torn side wall is usually caused by a brake pad that slips and rubs through the side of the tire or a sharp object that the tire has hit. When the sidewall tears, the tube will bulge through the sidewall and is quickly punctured. So if you do get a flat and put a new tube in without checking the tire you can flat again. ( Always check your tire before putting a new tube in it.) To be able to ride the tire you are going to have to repair the tear.
Preventive steps: Take a look at the sidewall while you are checking your air pressure (40 or more pounds for off road.) . What you are looking for is any fabric material that has shown fatigue or fraying. Pay special attention to the brake pads. Check the sidewalls for a thin black strip that can travel in a full circumference of the tire. If the pads are lightly rubbing against the sidewall, there is trouble ahead. Look for slices or objects that are puncturing sidewalls. If the sidewall shows a black rubber bubble protruding through, it's time for a new tire dude. Don't forget to adjust your brake pads.
Solution one: The standard way of fixing a slashed or torn sidewall would be to place something inside the tire in between the tube and the sidewall to keep the tube in and the elements out. Place the material inside the tire carefully so that it will stay in place while you inflate the tire. I have known of people using a folded over dollar, power bar wrapper, sandpaper from your patch kit, or the large patch out of your patch kit. Gray duct tape is the best solution, wrap some tape around your tire lever. You can also carry pieces of an old tire trimmed down to use as a boot.
PROBLEM: BROKEN DERAILLEUR CABLE
Problem: Cables can grow old pretty fast, from clamping and re-clamping, and can snap without much warning.
Preventive steps: Check front and rear derailleur cables for frayed ends, worn spots in the housing or crimping at the derailleurs. From continual tightening and loosening, the cables will smash and weaken, as a rule, at the clamping point. A healthy cable should keep its roundness and has no disturbance in the twining. Replace worn out cables before your next ride. Solder your cable ends to prevent fraying.
Solution one: If your derailleur cable breaks while you are on the trail, you will still be able to get home, but only in a fixed gear. When this happens you need to put your chain in a desired gear that fits the terrain you are riding and screw the high/low adjustment screws until the derailleur is lined up with that particular cog. The spring tension on the derailleur allows you to lock your bike into a single gear. For the front derailleur adjust the low adjustment screw into the desired chainring positioning so that it will hold it in that spot, preferably the middle ring.
PROBLEM: SEVERELY BENT WHEEL
Problem: This usually happens when a lot of force or weight is directed to the wheel or is hit hard on a foreign object, like a big rock.
Preventive steps: Check spokes for even tension by grabbing and pinching two together at a time, doing this throughout the wheel on both sides.
Solution one: A bent wheel has no respect for trueness. It will rub on your brake pads, your frame, your chain stays, you name it. If your wheel goes out of round you should be a able to get home by releasing the straddle cable on the brakes. Carry a spoke wrench and use your brake pads to help you true the wheel enough get home.
Solution Two: If your wheel is bent side to side, first you are going to have to release the brake and remove the wheel from the frame. Check for broken spokes and try to remove any if possible to keep them out of the way while riding. You can also twist them around the next good spoke. Next, place your bent wheel against a tree holding the bent sides, then with a few quick jolts try to bend the wheel back to ridable state. This process may have to be repeated a few times depending on the condition of the wheel. You want to use the tree as your pressure point and your arms and legs to put the wheel back to somewhat of a normal state. If you have a spoke wrench with you may be able to true some of the bad spots out of the rim. Remount the wheel on to your bike, you will probably still have to release the braking system or adjust it out so the brake pads do not rub on the rim. BE CAREFUL !
PROBLEM: CHAIN SUCK BETWEEN THE FRAME AND CHAIN RINGS
Problem: Chain suck usually occurs when trying to shift your gearing in extreme conditions, ie., quick transitions from a descent to a climb and trying to shift in the process, muddy wet conditions, dry chain, shifting out of adjustment, worn chain, and if your chain is not properly sized to your gearing. [A properly sized chain should be when the chain is off the bike, route the chain over the large chain ring in the front and the large cog in the rear without routing it through the derailleurs. When you do that, pull the chain snug with only two links overlapping each other.]
Preventive steps: Keep your drive train well maintained, keeping up on lubing the chain, cleaning, and replacing parts when necessary. Chains can usually last about forty to fifty hours of off road riding, depending on the conditions and the elements you are riding in. Muddy conditions (winter conditions) will wear a chain a lot faster than dry conditions.
Solution one: If you do get chain suck on the trail, you will not be able to pedal. What has happened usually is that your chain was in a slack position when it happened and it has wedged its self in between your frame and your chain rings. First, stop immediately , get off your bike and see how bad it has sucked up into the frame. In most cases you should be able to grab the chain and pull it back the same way it sucked up. You may have to use a little force. If it is still stuck you may have to detach the chain from the bike with the chain tool, then re-route the chain back through the drive train. Check for any kinks or twists in the chain before you install it back on your bike. This can cause problems in shifting if not checked before installation.
Solution two: If you do not have a chain breaker with you, use your 5mm allen wrench to loosen your chainring bolts to give the chain some room to possibly wiggle its way out of its bind, depending on the amount of space you have to work with you may have to pull the chainring completely off to allow for the chain to drop down. Don't lose any bolts and retighten firmly.
PROBLEM: BENT CHAIN RINGS
Problem: Chain rings will bend. The soft aluminium teeth can't hold up to rocks and logs. A bent chainring can cause problems while riding, ie., thrown chain, and chain suck.
Preventive steps: If your chain rings are bent, you will know it. Your biggest chainring is the most vulnerable of them all, mainly because it is the first to hit the obstacle. If your chainring is bent, it will grind on the inside of your front derailleur on every pedal stroke. A major bend will cause the chain to derail every time it comes to the bent area.
Solution one: Your crescent wrench out of your tool kit is going to be the best tool for the job in this case. Place the tool over the part of the ring that is bent, making sure it clears the chain rings teeth, keeping them from snapping off. Once you have the wrench in the proper position, push or pull the bent part very gently to try and realign the ring back to its normal position. If it is unrepairable put the chain in the middle chainring and just use your lower and middle ring until the upper ring can be replaced. Check the bottom bracket before you come to the conclusion that your chainring is bent, because you may have also damaged the bottom brackets spindle, and if so, start walking. Bent spindles do happen.
PROBLEM: BROKEN REAR DERAILLEUR
Problem: This can be a very unexpected event. With one blow, from a rock or stick, it can cause your derailleur to be snapped off. A broken rear derailleur causes your shifting to be very nonexistent, and will cause your chain to have too much slack.
Preventive steps: When you ride through really rough terrain and your rear derailleur is taking a beating from rocks and other obstacles it can cause the cast aluminum body to weaken and sometimes crack, then eventually break after it takes a hard enough hit. Remember you rear derailleur is on the right side and is low. Avoid hitting it if you can.
Solution one: Once the derailleur has broken you will have to remove the chain first, then pull the derailleur with a 5mm allen wrench. Place your chain in the middle chainring in the front and the middle cog in the rear. Using your chain tool, remove as many links until the chain is as snug as it can get around the drive train. You are going to be riding a fixed single gear, but it will get you home. The hills will be a bummer!
PROBLEM: FIRST AID AWARENESS
Problem: If a medical problem does arise while on the trail at least one person in the group should be prepared with a first aid kit.
Solution: Most common trail injuries are usually some sort of cut, scrapes, sprains, or bruises. Pre-packaged first aid kits are readily available through outdoor specialty shops and offer the essentials that you need while reading: ie., butterfly bandages, standard band aids, gauze, tape, disinfectant wipes, wire splint, ace bandage. Most first aid kits are small enough to fit into a fanny pack or large seat pack and do not weigh that much.
There are other precautionary measures to be taken while on a ride and that is to come prepared with the proper clothing, food, water, and other essentials. Wear a helmet! Use a water filter to obtain fresh water from lakes or streams. Have fun , and get back safely.