If you perform a procedure that requires bearings to be installed, make sure the parts are clean before you pack the bearings in grease. Grease can become contaminated with grit and break down over time.
You may wonder how these little metal balls are kept in place. They’re secured with something called a race. A tried-and-true race design, still popular after more than a century, is the cone-and-cup. In this design, a ring of bearings sits in a cup and is secured in place by a cone, which is screwed onto an axle or spindle.
The cone is typically adjusted to be tight enough so that there is no side-to-side looseness and the part (that is, the hub) rotates smoothly. Over-tightening could cause unnecessary force to be applied against the ball bearings, leading to wear and tear — not to mention the fact that it could make it much harder to pedal.
Bearings will either be in a “cage” or retainer ring, or be set as independent “loose” bearings. (Also, retainers are typical for all bearings on a bike, and perform inferiorly to loose bearings. The only benefit they have is convenience in building the bike).
One of the modern advances in bikes is the use of sealed bearing cartridges, which eliminate the need for adjustment or lubrication (less work for you!) and prevent grit and other contaminants from entering. Buy a bike with cartridges and you’ll save yourself the hassle of playing with tubes of grease and chasing bearings across your bike-shop floor.
Your inner gear geek may be disappointed if you use cartridges, because bearings are cool, shiny little balls that are fun to work with. Dennis feels like he hasn’t really worked on a bike until he’s juggled a few bearings in his hands and packed them in some fresh grease. But even so, cartridges do require less work.
Don’t Screw This Up: The Threading System
If you’re like most people, you probably think you know the basics of how threads work, but we promise you’ll be surprised by how much science there is to the basic concept behind a nut and bolt.
Why is this important? Of all the activities you’ll perform while working on a bike, tightening and loosening threads on a bike is at the top of the list. Improperly handle something as seemingly innocuous as a nut or a bolt, and you could irreversibly damage the threads of an expensive component on your bike.
Threaded fasteners are the unsung heroes of the biking world. Although they’re essential to keeping your bike together as it rolls on down the road, they’re so inconspicuous that people rarely notice them. About the only time they come to your attention is when something on your bike starts making a rattling sound, usually due to a fastener being loose.
Fasteners are heterosexual partners. They consist of a male part (such as a bolt) and hollowed female part (such as a nut), as shown in Figure 2-4. Male and female parts, designed to work together, are cut with complementary matching grooves that allow them to be threaded together.
Different fasteners are designed to handle different amounts of force. The bolt used to hold the water-bottle cage in place would not provide enough force to secure a crank.
Figure 2-4: Male and female threads on a nut and bolt.
Tightening enough, but not too much
The one thing you need to know about fasteners — and never forget — is this:
Never over-tighten a fastener.
When Dennis learned this concept, it was like a revelation. He had always assumed that the rule was: The tighter, the better. If someone had shared this all-important rule with him earlier, he could’ve saved himself from ruining a number of fasteners.
Fasteners stretch and flex when tightened, which gives the joint force to stay in place. Over-tightening the fastener can cause it to stretch to such a degree that the joint becomes damaged.
You don’t have to freak out the next time you have to tighten a nut or bolt. The general principle is to tighten it a bit, and then check it: If there’s still some play in the part, tighten it a little more.
If we’ve made you paranoid about over-tightening, you can always purchase a torque wrench. Bike mechanics use these in order to apply exactly the right amount of force when tightening a fastener.
If you’ve made like the Incredible Hulk and ended up damaging a thread, the folks at your local bike shop may be able to recut it using a tool called a tap. Of course, this assumes that the damage to the thread was minor and that there’s still enough undamaged thread remaining. If not, the thread may be irreversibly damaged.
Clean and lubricate all threads before tightening them. For smaller fasteners, a liquid lubricant will do the job. For thicker fasteners (such as the thread of a bottom bracket), a heavier lubricant such as grease is recommended.
When fasteners come loose
Sometimes a fastener will come loose. In many cases, this is the result of not being tightened properly. (Normally, vibration is not enough to overcome the force of a properly secured fastener.)
To prevent threads from loosening, bike manufacturers sometimes use devices such as locknuts or special washers to help hold the thread in place. Washers are used to help distribute the pressure around the bolt’s nut or head. They also reduce friction as the nut and/or bolt is tightened.
To increase the chances that a fastener will stay in place once it’s tightened, use a thread-locking compound. When this compound is applied to a thread, it hardens and expands, helping to keep the joint secure.
Shopping for threaded fasteners
When you’re shopping for threaded parts, keep in mind that threads are classified in a number of ways. One is according to the diameter from one side of the thread to the other. Threads are also measured based on how many threads are contained within a fixed length. Usually you will see measurements such as 1/2 inch x 20 tpi. The first number refers to the thread diameter, and the second number refers to the number of threads per inch. The important thing is not that you memorize what the two numbers mean but that you know that, if you have to buy a bolt, you’ll need to take a measurement like this when you go shopping. If you have a bolt in hand and need to buy another one, take it to your local bike shop. Just by eyeing the threads, the bike-shop staff will be able to help you.
For bolts, you commonly see an M before the measurement to represent millimeters. For example, the M5 bolt of a water-bottle cage is a 5mm bolt.
It’s not as important to know what the numbers describing a thread mean as it is to make sure the measurements of the old and new fastener match.
Considering How Cables Control a Bike
Despite the important role of bike cables, they rarely get the respect they deserve. They usually play second fiddle to their sexier companions, the shifters, brake levers, derailleurs, and brakes. The truth is, improperly installed or worn-out cables can prevent even the best derailleurs and brakes from functioning properly. When a squirrel jumps out in front of you while you’re hurtling down a hill on your bike, you’re not only counting on your brakes to grip the wheels and slow you down, but you’re depending on your cables to transfer the force from your clenching grip to the brakes.
Although cables have long been used to transfer force when pulled, bike cables are unique in that they have to transfer force around the curves and corners of a bike. The design of the cable with an inner wire supported by a stiff outer housing made of steel and covered plastic makes this possible.
Most bike cable housings have a liner made of plastic, nylon, or Teflon. This liner sits between the wire and the housing to help reduce friction. In older cables, wires didn’t have such a liner; because they came into contact with the housing, they required grease for lubrication.
In order to save weight and reduce the amount of friction, many bikes are designed to use cables with the inner wire exposed. The cable housing runs along a portion of the frame until it comes to a stop. The cable housing is fed into the narrow opening in the stop, which allows only the inner wire to pass
through. To ensure a snug fit in the stop, a small metal cap, called a ferrule, usually covers the end of the housing. From here, the wire continues on until it comes to another stop, facing in the opposite direction, where the cable housing begins again.
Not just any cable housing can be used with a bike. For index gears, you use a different style, higher-quality, non-compressing cable housing. It’s made with separate wires running parallel inside the housing and is held together by plastic.
Higher-quality cable housing for shifting shouldn’t be used for brakes, because it may not be able to handle the higher force applied during severe braking.
Less flexible non-compressing “gear” housing, though more expensive, is a different style and not necessarily higher quality. The only real benefit is that the index adjustment holds better than conventional housing. The failure rate of this housing is significant, and many people use brake housing for derailleurs anyway, although that usually means an additional adjustment to get the indexing correct.
The main consideration in the design of how cables work on a bike is eliminating friction so that force can be consistently transferred to the brakes or derailleurs. Cables that are too long create unnecessary friction and lead to a soft or spongy response. Cables that are too short may create kinks in the housing or limit your ability to fully turn from one side to the other.
Setting cable housing to the right length is important. If you’re replacing cable housing, measure them against your original housing. Keep them a little longer than you think you need — you can always trim off some extra length. If you cut your own cable housing, use cable or diagonal cutters.
After cutting the cable housing, examine the ends to see if any burrs were created. If so, you can recut the cable housing or file them down. After cutting the cable housing, you may have to open up the end of the housing with a tool, such as an awl.
If ferrules came with the cable package, attach them to the end of the cable housing. They protect and support the cable housing and help keep it in alignment with the stops.
You can buy cables in kits with inner wires, housing, and metal ferrules all included.
When running cables around a frame, you should try to avoid bends when possible. If you can’t avoid bends, make them as gradual as possible (as shown in Figure 2-5). If you’re replacing cables, use the cable path that was designed for the bike — an engineer took time to think this through.
For maintaining your cables, lubrication is useful to prevent rust. Use silicon, mineral oil, or a synthetic lubrication, and coat the cable before inserting it into the housing. Lubrication is also necessary for the parts that come in contact with the cables including adjusting barrels and anchor bolts, both of which have threads that need to be protected.
Don’t use grease to lubricate your cables — it creates too much friction and the dirt and dust from the road or trail will stick to the grease, causing even more problems.
Figure 2-5: A gradual bend in a cable is best.
Gearing Up
If your biking experience goes back as far as ours does, to when you climbed onto a tricycle for the first time and pedaled off to conquer the world, you may remember what it was like to ride with one gear. Cruising down the sidewalk at your parent’s side was pretty easy — at least until it started sloping uphill. You had to apply more and more force to keep your bike moving, until finally your little legs gave out and your parents had to turn around to head home.
Why was riding a tricycle uphill an impossible task? When a bicycle has no gears, each time you rotate the pedals, the rear wheel also rotates one turn. You rotation of your pedals will move your wheel one rotation (the full circumference of that wheel.) The force required to move that one rotation is much greater if you’re pedaling uphill. The idea behind gears is that the distance the wheel travels for each rotation of the pedals can be lengthened or shortened, allowing you to apply a consistent amount of force, regardless of whether you’re on an incline or decline.
Gears rely on the combination of the size of the front chainrings and the sprockets on the rear wheel of a bike. By switching between different sizes of chainrings and sprockets, gears allow you to use the same amount of force when pedaling, regardless of the terrain. Most bikes have two or three chainrings with 22 to 52 teeth between the largest and smallest chainring. On the rear cluster of sprockets, they have 11 to 32 teeth. Based on where the chain sits on the chainrings and sprockets, the rotation of the pedals will cause the rear wheel to have a different number of rotations.
For example, if the chain sits on a chainring with 44 teeth and a sprocket with 11 teeth, the gear ratio is 4 (44 ÷ 11), which means that, for every rotation of the chainring, the rear wheel will rotate 4 times. A higher ratio is ideal for going downhill or pedaling with the wind at your back. If the chain is on a chainring with 22 teeth and a sprocket with 32 teeth, the ratio is 0.69 (22 ÷ 32). A low ratio such as this is needed for climbing up a steep hill. (Is your head spinning as fast as your gears yet?)
The total number of gears on a bike is calculated by multiplying the number of chainrings by the number of sprockets. If your bike has 3 chainrings and 9 sprockets, you’re riding a 27-speed bike. On a bike with more gears, you’ll have a wider range of lower gears for going uphill and higher gears for going downhill. This also makes the changes in gear ratios much smaller, allowing you to more easily find a comfortable gear in which to pedal. Dennis’s touring bike has 27 gears and gives him great flexibility whether he’s huffing and puffing going up the side of a mountain or screaming down the other side at 50 mph.
When you’re buying a bike, keep in mind the following gear tips:
Choose a bike that has high enough gears to support faster speeds without your legs spinning at an uncontrollably fast number of revolutions.
Choose a bike that has low enough gears to enable you to climb hills.
Whenever possible, avoid gears that cause the chain to cross from the front to the back at an angle. For example, avoid locating the chain on the smallest chainring in the front and smallest cog in the back. This causes the chain to stretch and wear out and is bad for the sprockets.
Making Sure You Don’t Get Derailed
Anyone who has ridden a bike up a windy mountain pass or into a stiff headwind appreciates the ease of shifting into the appropriate gear with a click or twist of a shifter. The mechanism that makes shifting a nearly effortless activity is the derailleur.
To look at a derailleur, you’d think that it’s the most high-tech part of a bike. In reality, derailleurs are simple devices designed to move the chain between the different gears. Both the front and rear derailleurs are designed with a cage through which the chain runs. When you change gears with your shifter, the derailleurs force the chain to one side or the other until the chain falls or is lifted onto the chainring or sprocket next to it.
The front derailleur consists of a cage that, in a side-to-side motion, moves the upper part of the chain — the part that transmits power to the rear wheel. Because the upper part of the chain is under the force of your pedaling, it wants to stay in place. It’s more difficult to shift when you’re applying a lot of power and moving slowly.
Its more advanced partner, the rear derailleur, both pushes the chain from side to side and pulls it tight. The rear derailleur is designed to serve two main roles: moving the chain between the sprockets and keeping the chain under tension.
The mechanism controlling the rear derailleur is a hardened spring hidden inside. This spring is constantly pushing the derailleur away from the bike and toward the smallest sprocket. The cable attached to the bike’s shifter opposes the force of the spring. When the shifter pulls the cable, the cable overcomes the spring and moves the chain toward the bike and onto the next sprocket. When the shifter releases the cable, the derailleur again moves away from the bike. Tension of a second spring provi
des the resistance, which takes up any chain slack.
Rear derailleurs have a common design (see Figure 2-6). They have a cage that holds two pulleys in the familiar S-shape. The top pulley is the jockey pulley (also known as the upper jockey wheel); it guides the chain into what’s called the cage. The bottom pulley is the tension pulley (or lower jockey wheel); it’s designed to keep tension on the chain and take up slack.
Derailleurs are designed to maintain the appropriate amount of space between the jockey pulley and the rear sprockets as the derailleur moves back and forth. The derailleur also move its arm back and forth with each shift to keep its cage centered under the sprocket on which the chain sits. Usually, one or more screws are utilized to control the amount of lateral movement and spring tension.
The rear derailleur cage that connects the jockey pulley and the tension pulley has a length that varies depending on the amount of chain slack needed to be taken up. Models with longer cages are designed to support larger, lower-geared cogs and longer chains; they’re typically found on bikes with three chainrings. Rear derailleurs also have a maximum tooth capacity, which specifies the largest cog onto which it can shift a chain. Short cage derailleurs are found on racing bikes; they offer quicker shifting and higher ground clearance, the latter of which is important when cornering in tight curves.
Figure 2-6: A rear derailleur.
The Quickest Release in the West
On a cold day in the middle of a race in the Italian Alps in 1927, engineer and racer Tullio Campagnolo’s hands were so cold that he had trouble removing the wing nuts that held his wheel in place. This experience is supposedly what led him to invent the quick-release lever, something that has made lives easier for scores of bikers ever since.
Anyone who has ever had to remove a wheel on a bike without the benefit of a quick release knows just how much of a convenience Campagnolo’s contribution has been. Whether you’re taking off a wheel to quickly change a flat or to throw your bike into the car, the quick-release mechanism is virtually indispensable to biking.
Bike Repair & Maintenance For Dummies® Page 4
