EVERYTHING ABOUT MOUNTAIN BIKING
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Most mountain bikers who are well versed in the technical terminology that fills its pages. But then some of us is new to the game and probably stumble across phrases on the web and in the magazines that might as well have been written in Greek. To bring beginners up to speed, we went from one end of the mountain bike to the other, and compiled a dictionary of names and terms. So next time you walk into a cycling shop and say:"The price on a Noodle Tube Please..." see then who has the sheep face expression. Check it out...
SHOCK FACTS: THE PAMPERED DAMPER
Noleen Racing and Works Performance, both motorcycle suspension firms, made the first production hydraulic dampers specifically for bicycles. Motorsport suspension companies still dominate the mountain bike shock market, with Fox Racing clearly in the lead. This is what you need to know:
Eye-to-eye length: The distance between the center of the pivot locations on either end of the shock at full extension. This measurement is important when ordering a replacement.
Stroke: The distance that the shock compresses.
Damper: The body of the shock that contains the hydraulic fluid, piston and valving (same as shock body).
Damper shaft: The rod or tube that drives the internal damping piston.
Coil/over spring: The classic configuration that uses a metal coil spring, mounted externally over the shock body.
Airspring: A piston that acts against compressed air or gas to support the rider. Air springs are integrated into the shock body.
Negative spring: A short-travel spring inside the shock body that opposes the main spring to soften the first part of its stroke.
Compensator chamber (Also “separator piston”): a sealed piston that rides between the shock fluid and a chamber filled with compressed gas. As the shock shaft is plunged into the damper, the shock fluid displaces the compensator piston and compresses the gas in the chamber to compensate for the added volume of the shaft.
Piggyback chamber: The same function as a compensator chamber, but it is moved to a remote location to conserve space, or to shorten the shock’s eye-to-eye length.
Preload collar: A ring, threaded onto the shock body that supports one end of the coil spring. Turning the ring increases or decreases the starting spring tension. This adjustment is used to set the ride height (sag) of the rear suspension.
Progressively wound spring: A spring with its coils spaced closer together on one end to create less resistance when it is first compressed.
Blow-off valve: Any type of hydraulic valve designed to resist the flow of fluid until it reaches a predetermined pressure threshold. Usually used to protect a lockout-equipped damper from high-pressure damage.
Lockout: Any type of external hydraulic valve that prevents the shock from being compressed.
Free-bleed circuit: A hole or port that allows shock fluid to bypass the shock’s main damper piston during the compression and rebound cycles.
Low-speed compression clicker: A valve that restricts the free-bleed circuit during the compression stroke.
Low-speed rebound: Functions the same as the compression clicker as the shock is extended.
Sag indicator: Typically an O-ring on the shock shaft that gives a visual indication of how far the shock has been compressed.
Damper piston: A perforated piston attached to the shock shaft that reciprocates through the fluid inside the shock body. One-way valves on either side of the piston meter the flow of fluid to create compression and rebound resistance.
Spring rate: The amount of force that a spring produces when it is compressed one inch. If you placed a 300-pound spring on a bathroom scale and compressed it one inch, the scale would read 300 pounds—compressing it two inches would read 600 pounds.
REAR SUSPENSION TYPES — MONKEY MOTION JARGON
Dual-suspension bicycles represent the most technical aspect of the sport and thus, the least understood.
Four-bar linkage: Refers to systems with three articulating levers:
The swingarm.
The seatstay assembly
And a link that drives the shock. The fourth “bar” is the rear section of the frame between the swingarm and upper pivot locations. (Specialized FSR and Intense M-1).
Mac-Strut suspension: A conventional swingarm that drives a shock that is rigidly attached to the seat-stay assembly. (Titus and Turner make the best examples.)
Swing link: A link that serves no purpose other than to eliminate lateral stress from the shock assembly. (As on the Fisher Sugar and Jamis Dakar.)
Monoshock: A term stolen from circa ’70 Yamaha motorcycles that refers to a
triangulated swingarm with a single pivot near the bottom bracket. (Santa Cruz Superlight, Foes DH-Mono and Ellsworth Joker.)
Cantilever beam: The simplest design, it uses a large-diameter swingarm with a single pivot near the bottom bracket area (Rocky Mountain RM-7 and K2 Flying Monkey).
Parallel link swingarm pivot: A pair of linkage arms above and below the swingarm that allow it to swing in a different arc than a conventional single-pivot swingarm. (For examples see the Rocky Mountain ETS-X, KHS’s and Karpiel’s downhillers.)
Horst-link: Any rear suspension that uses a conventional swingarm linked to a seatstay assembly that is rigidly attached to the rear dropout. (Specialized FSR, Intense Tracer, Ellsworth Truth.)
Floating drivetrain (URT): When the bottom bracket is mounted to the swingarm instead of the frame. (The Ibis Bow Ti, GT i-Drive and Maverick American are modifications of the concept.)
Active suspension: Any suspension that reacts to bumps without being affected by braking or pedaling inputs. (Intense Uzzi, Specialized FSR, Ellsworth Truth.)
Reactive suspension (Also semi-active): Any design that is affected by braking and pedaling forces. (Giant NRS, Santa Cruz Blur.)
Progressive rate (Rising rate): Any configuration that amplifies the effects of the spring and shock as the suspension reaches full compression.
Falling rate: Opposite of progressive rate suspension.
Straight rate: A suspension system that causes the spring and damping forces to increase in direct proportion to its rate of travel.
Plain bearings (Bushings): The tubular sleeves of metal or plastic that the suspension’s pivot pins rotate within.
Sealed bearings Generally refers to cartridge-type ball bearings equipped with seals. “Cartridge” describes the fact that the balls, races and seals are permanently assembled into a single unit.
ALL ABOUT DISC BRAKES
In truth, rim brakes and hub-mounted disc brakes are two versions of the same technology. This means that all modern mountain bikes use some form of disc brake. For practical purposes, however, the “disc brakes” in this text are frame-or fork-mounted calipers that squeeze hub-mounted rotors.
Rotor: The “disc” part of the brake that attaches to the hub, usually made of stainless steel.
Caliper: The housing that encapsulates the brake pads and generates the clamping force between the pads and rotors.
Brake pads: A pair of steel plates with friction material bonded to the sides that face the rotors. Pads are retained by magnets or clips so they may be replaced easily without special tools.
Cable-actuated caliper (Also, mechanically actuated): Any type of mechanism other than compressed gas or hydraulic fluid, used to generate clamping force within the caliper. Most use threads or ball-ramps (Avid and Hayes make good examples).
Hydraulic caliper: The most common type of disc brake uses pressurized fluid to force one or more pistons against the brake pads.
Master cylinder: Rock Bottom’s Boss; nemesis to the Professor in old Felix the Cat cartoons. Also refers to the brake-lever-mounted piston and cylinder that drive fluid to actuate the brake
caliper.
Open hydraulic system: A master cylinder with a piston that retracts past a port that vents to a fluid reservoir. This allows heated fluid to expand into the reservoir when necessary. The self-adjusting open system pumps new fluid from the reservoir into the caliper as the brake pads wear (Hayes, Shimano, Magura, Formula, Grimecca and some Hope models).
Closed system: The simplest hydraulic system consists of a brake-lever-mounted piston that drives the caliper pistons through a connecting hose. The system is sealed, so fluid expansion due to heat and brake pad wear must be compensated for by external adjustments (Mountain Cycle, some Hope, and Cannondale brakes).
DOT type fluid: A caustic automotive brake fluid that eats some types of rubber and plastic seals (used on Hope and Hayes brakes).
Mineral oil: A non-reactive hydraulic fluid used for a wide variety of industrial and automotive applications (Shimano, Magura).
Bleed fitting: Hollow, hex-bolt screws with barbed heads that accept a plastic tube. Bleed fittings are used to vent air and fluid from the caliper.
Bleeding the system: A term for a method of pumping fluid through a hydraulic system to evacuate all traces of air. Air is compressible and thus causes hydraulic brakes to feel mushy and stop poorly.
Single-action caliper: A caliper with a piston or mechanical actuating system on only one side of the rotor (Magura Louise).
Double-action caliper: A caliper with pistons or actuating mechanisms on both sides of the rotors. May use a single pair or multiple pairs of pistons.
Four-piston calipers: Hydraulic calipers that use two pairs of small pistons that drive elongated brake pads (Shimano Deore XT, Magura Gustav and Grimeca). The purpose is to gain more braking force by moving the centerline of the braking surface further out on the rotor.
VEE BRAKES: CABLE-ACTUATED CANTILEVER RIM BRAKES
The vee-brake is the best-performing evolution of the traditional cable-operated bicycle brake. The first person to pen and produce the modern design for mountain bike use was Ben Capron, now a Specialized employee.
Caliper arms: Mirror-image lever arms that pivot on the frame bosses and clamp the brake pads to the rim.
Beveled washers: Hemispherical washers that allow the brake pads to be fixed to the caliper arms at angles to meet the rim surface correctly.
Brake pads: Plastic friction material attached to metallic posts that create braking friction. Pads are made of different compounds to adapt to wet conditions and different rim surface treatments.
Noodle tube: A curved metal tube that guides the brake cable through a 90-degree arc to the caliper arms.
Quick release: A slotted fitting that allows the noodle tube to be removed from the caliper arm. This function allows you to open the caliper arms wide so the tire can be removed past the brake pads.
Parallelogram: Shimano XTR and other vee-brake designs use a parallel linkage mechanism to move the brake pads along a straight line into the rim. This causes the pads to wear more evenly, and prevents the pads from arcing into the sidewalls of the tire.
Centering screws: A pair of screws, one on each caliper arm, that adjust the return spring tension. Use this adjustment to space the pads equally from the rim surface and to increase or decrease the feel of the brake return springs at the brake lever.
Brake lever: Handlebar-mounted hand levers.
Leverage adjustment: Some brake levers have manual adjustments that move the brake cable farther from or closer to the lever’s fulcrum (pivot location). Moving the cable farther away decreases braking force and causes the lever to feel firm—moving it closer to the fulcrum has the reverse effect (Shimano XTR and Deore XT, Avid Speed Dial levers).
Barrel adjuster: A threaded, tubular cable-housing stop. Rotating the barrel adjuster is a convenient way to take up cable slack, or to change the distance that the brake pads ride near the rim’s surface.
Brake bosses: Posts attached to a frame or fork that function as the brake pivot locations.
Brake cable (Brake wire): The steel cable that operates the brakes. Brake cables have a barrel-shaped metal anchor soldered to one end, perpendicular to the wire.
Cable housing: A spiral metal tube coated inside and out with smooth plastic that acts as a reinforced lining for the brake cable to slide within.
Cable ferrule: A metal or plastic cap that fits onto the ends of the cable housing.
Toe-in: When the brake pads are aligned with the rim at an angle so that the end of the pad facing forward touches the rim slightly before the opposite end.
MOUNTAIN BIKE SKELETON — IT’S CALLED A CHASSIS
Yeah, I know this is basic, but even Sir Ned Overend didn’t know what a chainstay was at some point in his life. This visual aid will help you become familiar with the essential functions of a mountain bike’s frame and components.
Chassis: A fancy term that refers to the frame, fork and suspension as one unit, or that can be used to describe the frame only.
Headtube: The tube in the front part of the frame that the fork passes through.
Headset: A pair of ball-bearing assemblies, pressed into the head tube, that the fork rotates on.
Top tube: The upper member of a conventional frame. Its length determines the proper fit for different sized riders.
Down tube: The lower member of a conventional frame.
Gusset: Any reinforcement that is added to a frame tube that serves to strengthen it. Gussets are normally found under the downtube/head tube junction.
Water bottle bosses (bottle mounts): Threaded fittings that fit bolts for water bottle cages.
Bottom bracket shell: The lowermost tube of the frame that houses the crank axle mechanism can be either 68mm or 73mm wide. The left side is threaded clockwise (the standard direction); the right side is threaded counterclockwise.
Bottom bracket: An ancient name for the axle, bearings and bearing housing that the crankset rotates around. There are three main designs:
Square taper (the industry standard).
Shimano splined axle (fits upper-level Shimano cranks).
Isis splined axle (fits Race Face, Truvativ, FSA and other aftermarket cranksets).
Seat tube: The frame member between the bottom bracket and the top tube that the seatpost is inserted into.
Interrupted seat tube: A frame that uses a short seat tube that does not continue to the bottom bracket—typically used to make room for rear suspension.
Cable guides: Any of a number of fittings that are attached to the frame to route cables, cable housings and brake hoses.
Brake bosses: Threaded posts attached to the frame and fork that act as pivots for caliper brakes.
Seatpost: The tubular part sized to slide into the seat tube that allows you to adjust the position and angle of the saddle.
Seatpost clamp: An aluminum clamp that fixes the height of the seatpost. Many bikes use a quick-release mechanism here to lower the seat for technical riding.
Chainstays: The lower pair of tubes that connect the frame to the rear wheel.
Swingarm: The lower frame member of a rear suspension system that spans from the bottom bracket to the rear wheel; performs the same function as chainstays.
Rear dropouts: The fittings that secure the rear wheel’s axle and the rear derailleur to the frame.
Seatstays: A pair of tubes that span between the rear axle and the upper part of the frame, or its counterpart in a rear suspension system.
Caliper mount: A rigid fitting that fixes a disc brake caliper to a frame or fork. There are two different types:
A-type mounts: (A side-mount flange that fits most disc brake types)
Post mount: (A pair of threaded bosses that fit the underside of Hayes-type calipers.)
Butted tubing: Any tube with walls that are thicker near the ends than in the center. Taper-butting is the same process, except that the end segments have a gradient in the thick sections.
Swaged tubing: A mechanical operation that forces a section of a tube to be larger in diameter. Swaging also can be used to change the shape of a tube to a taper, rectangle, ect.
Hardtail: A bicycle equipped with a suspension fork that has a conventional, unsuspended frame.
Softtail: A dual-suspension bicycle with minimal rear wheel travel. Most use a simple spring instead of a hydraulic shock and use frame flex instead of mechanical pivots to actuate the rear suspension.
Monocoque: A frame member that uses a hollow, box-shaped structure instead of tubing or a solid bar to carry the load. Monocoque frames are usually aluminum or composite construction.
Dropped top tube: A tube that is bent in the center, or made in two pieces to create more stand-over clearance for the rider.
Seat mast: The frame member that supports the short seat tube on an interrupted-seat-tube frame design.
FORK TALK — THE EMPIRE THAT PAUL TURNER BUILT
Telescopic fork: All suspension forks that operate by tubes sliding inside other tubes.
Steerer tube: The center tube of a fork that rotates on the headset bearings inside the frame’s head tube.
Fork legs: The two upper members of the fork that connect to the crown (also called the stanchion tubes).
Fork crown: The bridge that connects the steerer tube to the legs.
Tripleclamp: A motorcycle term that refers to the fork crown “clamping” the two legs and the steerer tube together.
Dual-crown fork: Also called “double, tripleclamp fork” uses a pair of crowns; one above the head tube and the other below to support the fork legs.
Through-axle: A large-diameter axle that either threads or clamps directly onto the fork lowers for extra rigidity.
Fork seal: A plastic insert that grips a sliding surface to prevent air, crud, or fluids from migrating from one area of the fork to another.
Dust wipers: Looks like a fork seal, but functions primarily to prevent abrasive material from entering the fork.
Fork boot: Either a corrugated tube or a cap that covers the sliding surface of a fork leg to prevent abrasive particles from entering the fork.
Air fork: Generally refers to a suspension fork that uses compressed air as its main spring in lieu of a coil spring.
Spring fork: Uses one or more coiled steel springs to suspend the fork.
Damper: Any type of friction device used to control the rebound forces of the fork spring. Most forks have hydraulic dampers that force light-viscosity mineral oil through various restrictor circuits to create damping forces.
Washer stack: A number of wafer-thin, flexible steel washers used to restrict the primary flow of fluid through a hydraulic damper.
Damping clickers: External knobs used to control the flow of fluid through the fork’s damper. Clickers are used to set the fork’s low-speed damping.
Fork arch: A bridge that connects the right and left sliders of a telescopic fork to increase its torsional stiffness.
Spring preload: An adjustment that pre-compresses a fork’s coil-type main spring. Preload is used to preset the exact amount that a fork will settle under the weight of its rider.
Lockout: An external device that prevents fluid from flowing from one side of the damper to another, and thus prevents the fork from moving.
Sliders (The fork lowers): The part of the fork that is attached to the front axle—generally refers to the castings that telescope over the legs of a conventional fork.
Inverted fork (Upside-down fork): a design developed for motorcycles that uses large-diameter legs for added stiffness. The smaller-diameter lower tubes telescope into the uppers.
Negative spring: A short-travel air or coil spring that works in the opposite direction of the main spring to soften the first part of the fork’s travel.
Oil-bath damper: A hydraulic damping cartridge that is immersed in shock fluid. The cartridge draws and vents into the surrounding fluid “bath” as it cycles.
Cartridge damper: A sealed hydraulic damper that is contained within a fork.
Stroke (Same as fork travel): The entire distance that a fork compresses.
Fork sag: The distance that the fork settles into its stroke under the weight of the rider and bicycle (same as “ride height”).
DERAILLEUR — TALK DERAILLEURS, SHIFT LEVERS, CRANKSETS, COGS AND CHAINS
Trigger shifters: Generally refers to Shimano RapidFire shift levers. A pair of handlebar-mounted levers, one operated by the thumb, the other by the index finger.
Twist shifter: A rotating hand grip that operates a derailleur cable.
Derailleur cable: A steel cable, much thinner than a brake cable, with a small cylinder-shaped stop soldered to one end, parallel to the wire, and also a metal-reinforced outer sleeve that it slides within.
Derailleur housing: Derailleur housing is distinctly different from brake housing because it is rigidly reinforced with a number of steel wires wound at 60 degrees around a central plastic tube. This configuration prevents the cable housing from compressing lengthwise to insure accurate shifting.
Cogs (Cogset): The cluster of sprockets that graduate from a small number of teeth to larger numbers from right to left, attached to the rear hub. Cogsets are available in various diameters that allow cyclists to choose higher or lower gear ratios. Cogsets are bound together in sets of 7, 8, or 9 sprockets.
Gears (Gear ratios or speeds): Bicycle jargon for the combinations of front and rear sprockets. Most mountain bikes use three sprockets up front and nine in the rear, which multiplies out to 27 gears.
Chain rings: Bicycle jargon for the sprockets attached to the crankset.
Crankset: A group of parts that
includes the crank arms that hold the pedals and the drive sprockets. The crankset is bolted to the bottom-bracket axle. Crank arms come in lengths from 165mm to 185mm, measured from the center of the pedal axle to the center of the bottom-bracket axle. Mountain bikes typically use 175mm arms.
Shifting ramps: A section of a sprocket where the teeth have been modified or pins have been placed to help the chain move from one sprocket to another more easily.
Freewheel (Overriding clutch): A one-way clutch that allows the cogs to stop while the rear hub rotates.
Freehub: A hub design pioneered by Shimano that incorporates the freewheeling clutch into the hub design to improve shifting and strengthen the axle. The free hub was key to the development of successful index shifting.
Index shifting: Any shifting mechanism that has a defined stop that signals each gear selection.
Rear derailleur: A remotely controlled device that guides a roller chain from one sprocket to another. A conventional rear derailleur has 12 major parts.
Upper pivot body: The primary member of the derailleur that swings on the rear dropout.
Parallelogram arms: A pair of links that swing the jockey cage over the cogs.
Jockey cage: A pair of plates housing two pulleys designed to tension the chain and take up slack.
Lower pivot body: Houses the tension-spring and bearing that the jockey cage rotates around.
Jockey pulleys: A pair of small sprockets that guide the chain through the derailleur and move over to align with each cog.
Return spring: A spring between the parallelogram arms that opposes the derailleur cable and causes the derailleur to shift from the largest to the smallest cog.
High and low adjustment screws: They establish the distance the derailleur can swing across the cogs.
H—B-tension screw: An adjustment near the upper pivot that prevents the upper jockey pulley from riding on the largest cog.
Barrel adjuster: The cable tension adjustment screw that the derailleur housing terminates into is used to fine-tune shifting.
Front derailleur: A remote-controlled device that moves the chain from one chainring to another and consists of six major components:
Clamp body: Houses the cage pivots and adjustment screws and functions as a clamp to fix the derailleur to the frame’s seat tube. (Clamps are available in various sizes that correspond to seat tube diameters.)
Parallel arms: A pair of links that move the derailleur cage over the chainrings.
Cage: A pair of shaped steel plates that are parallel with the chain. Depending on the direction of the shift, one plate acts to force the chain onto the next sprocket while the other serves as a guide to prevent the chain from over-shifting.
Return spring: A stiff spring that acts against the derailleur cable and causes the derailleur to shift from the largest to the smallest chainring.
Adjustment screws: A pair of screws on the derailleur body that determine the outer limits that the cage can travel.
F—Top-pull/bottom-pull: Refers to the direction that the cable enters the derailleur mechanism in relation to the frame (important to know when ordering a replacement).
Derailleur chain: Narrow roller chain that is specifically designed to run smoothly at an angle. Derailleur chain is generally riveted into one continuous loop and must be pressed apart to remove it from the bicycle. Because cog spacing varies between brands, derailleur chains must be ordered to fit.
Lower gear: A larger rear sprocket or a smaller front sprocket.
Higher gear: A smaller rear sprocket or a larger front sprocket.
Granny gear: The lowest gear ratio available—the smallest chainring matched with the largest cog.
Cross-chaining (Same as cross-over gear): An undesirable gear selection where the chain runs between the innermost chainring and the outermost cog (or the opposite). This configuration causes undue wear on the transmission components.
Chain guide: Generally used for downhill, a pair of circular plates that surround a single chainring, combined with rollers above and below the crankset that keep the chain from derailing over rough terrain.
Freewheel cog: Used on single speeds, it is a freewheeling clutch fixed to a single sprocket. The assembly threads directly onto a special hub.
Internally-geared hub: Any type of rear hub that houses a multiple-speed, geared transmission (Shimano Nexus, Rohloff).
One-key release bolt: A crank arm retaining bolt with a special cap that traps the bolt and uses it to press the crankarm off the bottom bracket axle (Shimano XTR).
HEADSETS — HOW TO SPIN A FORK
Headset bearings were once the greatest problem area of a mountain bike. Now, the reverse is true. A headset consists of all the parts between the fork and frame.
Threaded headset: An early design that required fine threads on the top of the steerer tube and upper headset retaining cups. The design is no longer used because the short threaded section of the steerer tube required custom sizing to fit frames with different-length head tubes.
Threadless headset: Generally refers to the Cane Creek patent and its derivatives that use an upper race assembly which slips onto the fork steerer. The headset bearings are fixed in place by an externally clamped handlebar stem. The design essentially makes one fork fit all frames and greatly simplifies bearing adjustments.
Press-in cups: Refers to machined bearing carriers that are pressed into the upper and lower faces of the frame’s head tube. The cups can house all or part of the headset bearings.
Upper race: The uppermost section of the headset that contains all or part of the bearing. The threaded part of an older headset.
Crown race: A metal ring on the lowermost part of the headset that is pressed onto the fork steerer and lies against the fork crown. It acts to align the lower bearings on most designs, but the curved ball bearing race is machined onto this part on inexpensive headsets.
Cup-and-cone bearings: Used on most inexpensive types, the “cup” race surrounds a ring of ball bearings and the “cone” race rides inside the ball’s circumference.
Cartridge bearings: One-piece sealed bearings that are pressed into the headset or frame.
Internal headset: When the frame’s head tube is machined to fit the headset bearings directly, thus eliminating the need for press-in cups. Klein and Cannondale popularized this process.
Contact seals: Generally refers to flexible plastic rings that are installed between the headset cups to prevent contamination of the bearings. Can describe a type of seal found on cartridge bearings.
End-play: A slight amount of fork wobble caused by small amounts of space between the headset bearings. A sign that the headset needs adjustment.
Brinelling: An engineering term that describes depressions formed into the bearing races by the balls due to excessive pressure. Brinelling causes the headset to bind and reduces steering control.
“Star-Fangled Nut”: A cheesy term that describes the threaded fitting that is pressed into a fork steerer to aid in adjusting a threadless headset.
Headset cap (Stem cap): A fancy washer that is used in conjunction with a 6mm Allen screw to draw a fork steerer tube through the stem to adjust a threadless headset.
Threadless stem: Any type of handlebar stem that clamps onto a bare steerer tube.
Quill stem: The old-fashioned stem type that slides inside the fork’s steerer tube and is fixed by an internally expanding wedge.
One-Point-Five Standard: An oversized, 1-1/2-inch steerer tube configuration, and a correspondingly oversized, conventional threadless headset assembly intended for long-stroke, single-crown forks.
Headset spacer: Primarily used to adjust the stem-height of threadless headsets, the spacers vary in height from 5 to 15mm and slide over the fork steerer above and below a clamp-on stem.
ALL ABOUT WHEELS — RIMS SPOKES AND HUBS
You wouldn’t think that there is a lot to learn about wheels until you need to order a pair at a bike shop. Take the time to understand wheels and the rest of the sport will unfold at your feet.
Wheel: The sum of all the components, including hub, spokes, spoke nipples, rim, and sometimes the tire and tube. “Wheelset” is a paired front and rear wheel.
Hub: The central part of a wheel that houses the bearings and axle and anchors the spokes.
Freehub: A rear hub that incorporates a freewheeling clutch.
Single-speed hub: Refers to a special rear hub with wider-spaced spoke flanges and a thin threaded flange on the right side that accepts a single-cog freewheel.
Disc brake hub: Any hub with a drilled and threaded flange that accepts a disc brake rotor.
Through-axle hub (Also thru-axle): Generally, an oversized, sealed-bearing hub that accepts a large-diameter axle which can be pulled free from the hub in order to remove the wheel. Most through-axle designs are specific to downhill bikes.
Hub width: Refers to the hub’s measurement between the faces that engage the inside of the dropouts. Most mountain bikes use 135mm-wide rear hubs and 100mm-wide front hubs. Downhill-specific hubs are up to 25mm wider.
Cup-and-cone bearings: Old fashioned, adjustable bearings that use a threaded-on inner “cone” race that traps ball bearings inside a bowl-shaped “cup” race that is pressed into the hub. Until the late ’80s, when sealed cartridge bearings became the mountain bike standard, almost every bicycle used this type of hub bearing.
Cartridge bearings: One-piece ball bearing assemblies that are pressed into the hub shell.
Quick-release axle: A hollow axle that does not protrude past the outside of the dropouts to allow the use of a quick-release mechanism.
Quick release: A type of over-center clamp that uses a rotating cam inside a housing to draw a shaft through a hollow hub axle in order to fix the hub to a frame or fork.
Spokes: Generally, threaded high-strength wire that, when tensioned and laced properly, transfers the weight of the rider to the rim. Aluminum (Mavic CrossMax) and composite spokes (Spinergy) are available, but are not widely used.
Butted spokes: Not necessary, but very common. Butting refers to a thicker section of the spoke shaft, generally near the threads and head, that adds strength and durability to these high stress areas. The proper way to describe a butted spoke is by its wire gauges (14/15 gauge spoke) or its diameter in millimeters (2mm x 1.5mm spoke). These are the most commonly used for mountain bikes.
Rim: A circular shape, generally extruded from aluminum alloy, that a conventional tire can be mounted to. The parts of a mountain bike rim are as follows:
Flanges: A pair of hooked ridges designed to catch the reinforced “bead” of a tire.
Braking tracks: Flat sides with smooth surfaces that interface with conventional rim brake pads.
Spoke holes: Two rows of equally spaced holes that interface with the spoke nipples. Spoke holes may or may not have metal reinforcement “ferrules.”
Well: A depressed section between the rim’s flanges that facilitates the removal of the tire bead.
Valve hole: There are two diameters: the smaller “presta valve” size, and the larger, automotive “Schrader” valve sized hole.
Box-section rim (Also, double-walled): A hollow cross section in the rim extrusion used to add stiffness.
Single-wall rim: A thick extrusion with no hollow cross-section that is rarely used for mountain bikes.
Disc brake rim: An extrusion designed without a brake track on its sides. (Any conventional rim may be used with disc brakes).
Tubeless rim: A rim designed to hold air. Tubeless rims usually have a box-section profile without the usual spoke hole perforations in the outer wall in order to create an air seal. Special O-ring-sealed valve stems are a requirement (Mavic UST).
Welded rim: A construction technique that melts the rim extrusion together with pressure and an electrical arc.
Pinned rim: Any type of internal pressed-in fitting that is used to complete the rim extrusion into a circle.
Ceramic coated rim: A type of ceramic, dark gray in color, that is applied to the rim’s braking track, usually with an electric plasma arc. The rough, abrasion-resistant surface improves the life of an aluminum rim and stops better in dry conditions.
One-piece wheels: Various types of carbon fiber and cast metal mountain bike rims have been introduced over the past two decades with poor performance results. The advantage of a cast or molded wheel is that it should never need truing (straightening). Avoid this area of technology.
Spoke lacing: Both an art and a science, lacing refers to the number of spokes used to build a wheel and the method in which the spokes are woven together. Here are the high points:
Spoke count: Most mountain bikes have 32 spokes per hub—a number that has proven to produce the lightest and most reliable bicycle wheel. Hubs and matching rims are made for 48-, 36-, 28-, and 24-spoke wheels for special purposes.
Cross: Crossing the spokes as they leave the hub flanges reduces the stress on the hub flange and increases the strength of the wheel when using disc brakes. The crossed spokes are counted from the hub flange out. Most wheels use a “three-cross” pattern. One-cross, two cross and four-cross patterns are used for special applications.
Radial lacing: A fancy-looking pattern with each spoke radiating directly from the hub to the rim without crossing any others. Radial lacing creates a laterally rigid wheel, but tends to overstress the hub flanges. It is also undesirable for disc brake wheels.
Weaving: Crossed spokes are woven together at the outermost intersection to cause some of the wheel’s stresses to be transferred to adjoining spokes. Weaving the spokes has also proven to extend the lifespan of a wheelset. Fancy twisted spoke lacing serves no purpose except to impress non-cycling beach goers.
Tension: Spokes must be stretched slightly so they won’t go slack when the wheel is deflected. The perfect wheel is fine tuned so that every spoke is equally tensioned. When the rim of a properly tensioned wheel hits a bump, it deforms slightly, and momentarily increases the tension of all spokes. Uneven tension forces fewer spokes to do more work. Over-tightening the spokes can bring the wheel’s components to the breaking point, leading to premature failure. (Top wheel builders use a gauge as a final check.)
Paired spokes: A minimally-spoked wheel that uses paired crosses of spokes on opposing sides of the rim to maintain a higher degree of lateral strength than would be possible using a standard lacing with an equal number of spokes. A rigid rim is an essential component of this exotic-looking configuration (popularized by Trek, and Shimano).
TIRES AND TUBES — WHAT WE REALLY ROLL ON
Dumb luck is as important as cutting-edge science when it comes to designing a successful mountain bike tire. The following tire lingo should get you up to speed:
Beads: The pair of reinforced lips that interface with the inside edges of the rim. The tire’s beads do not expand when the tire is inflated and thus keep the tire on the rim.
Kevlar tire (Also folding tire): A tire with the beads reinforced with flexible aramid fibers instead of the typical steel wires that line most commercial tire beads. Kevlar is Dupont’s trade name for the material. Kevlar fabric is rarely used elsewhere in the tire.
Carcass: Refers to several bonded layers of nylon cloth and rubber that support the tread and give the tire its strength.
Tread: A thick layer of rubber that is molded onto the carcass. Tread rubber is formulated into hard and soft compound depending on the aggressiveness of the tread design.
Hot patch: The fancy lettering and logos that adorn most tires, which are hot-pressed on in the final manufacturing operation.
Bead-filler rubber: A thick layer of rubber that is applied between the cloth layers of the carcass near the beads to stiffen the sidewalls and reduce impact damage. Usually found only on downhill and freeriding tires because of the added weight.
Plies: Refers to the number of cloth layers in the carcass under the tread.
Size: A confusing measurement molded onto the tire’s sidewall. The standard rim size that any mountain bike tire will fit is 26 by 1.75 inches. The width of the tire is considered its size. Most manufacturers measure the width of the carcass; some use the widest part of the tread. The average width of a cross-country mountain bike tire is 2.0 inches. Downhill and freeriding tires range from 2.2 to 3 inches wide. A number of mountain bikes use smaller-diameter, 24-inch rims, and the matching tires share conventional widths and tread patterns.
Knobby tread: Any aggressive tread design with tall, individual blocks.
Racing slick: A narrow, lightweight tire with a smooth tread pattern at the top of the tread and small edging tread block near the sides. Used for cross-country racing because they roll faster.
Semi-slick: A more aggressive racing tread pattern that retains the minimal center-tread design.
Sticky tread: An ultra-soft rubber compound used primarily on downhill racing knobbies. Small rocks and sand actually adhere to the rubber, hence its name (Intense and Tioga tires).
Butyl tube: A type of synthetic rubber that retains air well and is used to produce most of the world’s inner tubes.
Natural rubber tube (Also latex tube): Natural rubber is stretchier than synthetics and can be made into a lighter weight innertube—and is believed to better resist punctures. In practice, latex tubes are unreliable and expensive.
Schrader tube: Refers to any tube with an automotive-type filler valve.
Presta tube: Any tube with a small-diameter “French-type” filler valve. The presta valve is lighter weight and better suited to high-pressure applications because its valve seat can be threaded tightly closed.
Rim strip: A liner of special tape or a band of rubber that protects the inner tube from the sharp edges of the rim’s spoke holes.
Tubeless tire: A conventional tire that has been sealed to retain air and uses a modified bead designed to seal against a special sealed rim. (Mavic, Continental, Kenda, Michelin, Hutchinson and Specialized.)
Slime tubes: A proprietary brand of sealant injected into a ready-to-use innertube. Jargon for any inner tube that has been injected with puncture sealant. (Slime, Stan’s No-Tubes).
Pinch flat (Also, snake-bite puncture): The most common off-highway flat is caused by a harsh impact that compresses the tire against the rim flanges. The tube shears in two places as it becomes caught between the folds in the tire carcass.
IN THE COCKPIT — THE PARTS YOU SIT ON, STAND ON AND HOLD ON TO
We sense what is going on through the handlebar grips, saddle and pedals. Those are the components that interface with our human form.
Seatpost: Any pillar that is designed to hold a bicycle saddle and telescope into a tubular frame member. There are three distinct designs categorized by the method by which each clasps the seat rails:
Twin bolt mechanism: This is the most time consuming to adjust, but also the most reliable. A pair of bolts under the seatpost head squeeze down on a pair of plates above and below the seat rails. By balancing the tension of the screws, you can fine-adjust the tilt of the saddle (Thomson, Syncros, Race Face).
Laprade type: The head of this design has a curved track that the clamping head nests into. The saddle tilt is adjusted by rocking the clamp head in the curved track and tightening a single Allen screw (Control Tech).
Lay-back type: Any clamping mechanism that is set back from the centerline of the seat post (Ritchey).
Seatpost sizing: Diameters range in millimeters from 26.4mm to 38.6mm in no useful order. The smaller-diameter racing standard is 27.2mm or 26.8mm, Oversized seatposts begin at 28.6mm and up.
Racing saddle: A long, narrow, lightly padded seat that provides a variety of cycling positions—none all that comfortable (nearly all modern racing saddles were patterned from the Selle Italia Flite Titanium).
Male-saver saddle: Any seat design with a relieved center section to take pressure off of certain nerves and blood vessels that are known to cause manly part numbness.
Female saddle: A shortened saddle design with a slightly wider tail section that fits the female pelvis and riding position more comfortably (Juliana, Specialized and Fiziks).
Seat rails: A pair of metal rails that run parallel under the seat to allow fore/aft adjustment.
Clip-in pedals: Any type of dual-sided pedal with a catch mechanism that interfaces with a shoe-mounted cleat.
Spud type pedals: Shimano SPD clip-in pedals, or copies of the design, that engage a small cross-shape steel tab centered in a groove that runs the length of the underside of the sole of a matching shoe.
Platform pedals (Also, flat pedals): borrowed from BMX, these wide, studded pedals are used without clip-in bindings, primarily for downhill and freeriding purposes.
Flat bars: Handlebars with two mild bends and no “rise” that are used for cross-country racing and moderate cross-country purposes. The most efficient bar for extended climbing.
Riser handlebar: An adaptation of the old-fashioned cruiser bar that is bent to sit higher over the head tube for more comfort and control.
Bar ends: Short clamp-on handlebar attachments that emulate the hand position of a road bike for more effective climbing.
Four-bolt stem: A stem with a removable handlebar clamp. Can use two bolts to accomplish the same purpose. Some riser handlebars will not slide into a one-piece stem clamp.
Stem rise: The angle of the stem in degrees in relation to the steerer tube. Most mountain bike stems are between five and ten degrees.
Stem extension (Also stem length): The distance between the center of the steerer tube and the center of the handlebar measured along the stem’s extension tube.
A-Head stem (Same as threadless stem): Uses a clamp to fix the stem to the fork’s steerer tube.
Shorty stem: Any stem with less than a 90mm extension.
Zero-rise stem: Any stem that extends perpendicular to the fork’s steerer tube.
Negative-rise: A stem with an extension that angles below a perpendicular line from the fork steerer (some Cannondale XC bikes).