Bike Edmonton

The Spoke Curriculum - Session 3

Shifting

Description

Demo how shifting works

Details

Content

Primary Content Instructor Notes
Derailleur bicycles have several sprockets on the rear hub. By using different combinations, you have low gears for going up hill and high gears for going down hill.

Rear derailleurs "derail" the chain from one sprocket and move it to another. The upper pulley pushes the chain between sprockets. Proper adjustment aligns this pulley under the intended sprocket.

The derailleur is controlled by a cable, which runs inside the cable housing. Pulling the cable moves the derailleur in one direction and tightens the derailleur's spring. Relaxing cable tension allows the spring to move the body in the opposite direction.

Derailleur pulleys are limited in both inward and outward motions by using the derailleur limit screws. Properly set, the derailleur will shift to both the extreme outward sprocket (the smallest in size) and the extreme innermost sprocket (the largest in size). The limit screws do not control the derailleur on the sprockets between the two extremes. The limit screws are usually marked "H" and "L" (high gear and low gear). The "H" controls the outer most limit of the derailleur, and the "L" controls the inner most limit.

Rear H-Limit

  1. Shift chain to outermost (largest) chainring (front). Shift chain to outermost rear sprocket (smallest sprocket).
  2. Check tension on rear cable. If cable appears to have any tension, it may interfere with the H-screw setting. Turn adjusting-barrel clockwise to eliminate cable tension, or release the cable entirely. Proper cable tension (indexing) will be adjusted later.
  3. Pedal the bike at a quick cadence (about 60rpm or more).
  4. Pull the cable by hand until the chain shifts one sprocket inward. Release the cable quickly and observe the chain shift. It should move quickly back to the highest gear.
    1. If it moves too far (falls off), stop pedaling. Replace the chain on the smallest sprocket, and tighten the H-screw until the upper pulley appears in-line with the smallest sprocket.
    2. If it is sluggish to shift to the smallest cog, or the inside of the chain makes noise from rubbing against the next sprocket, loosen the H-screw by 1/4 turn.
    3. If the shift appears acceptable, tighten the H-screw by 1/4 turn.
  5. Keep adjusting, tightening just until symptoms of a too-tight H-screw appear. Then loosen by 1/4 turn increments just until the symptoms disappear. When too tight symptoms disappear, H-screw is at tightest acceptable setting, and limit screw setting is done.

Rear L-Limit

The L-limit stops the derailleur from moving inward (toward the spokes). The limit screw does not make the derailleur move, pulling the inner wire makes the derailleur move. The L-screw allows the pulley wheels to shift the chain to the innermost sprocket and yet not shift off the sprocket into the spokes.

  1. Shift bike to middle chainring (or smaller ring of double chainring bikes) and to second-to-innermost rear sprocket.
  2. Pedal bike at a quick cadence.
  3. Pull cable by hand to shift derailleur inward. Release cable quickly and observe the shifting.
    1. If it moves too far (into spokes), stop pedaling, replace the chain, and tighten the L-screw until the upper pully appears in-line with the largest sprocket.
    2. If it is sluggish to shift to the innermost gear when pulling on the cable, loosen the L-screw 1/4 turn.
    3. If shifting seems adequate, tighten the L-screw 1/4 turn and check again.
  4. Keep tightening until it is too-tight, and then loosen by 1/4 turn increments just until shifting is appropriate.

B-Screw Adjustment

If the pulley rubs against the innermost rear cog, tighten the screw on the back of the derailleur to pull the pulley back and away from the cog.

Rear Indexing

Note: If the cable is not correctly routed into the derailleur pinch bolt, a good indexing setting may not be possible. The wire should leave the barrel adjuster and travel straight to the pinch mechanism.

  1. Set limit screws (if not already done).
  2. Shift chain to outermost rear sprocket (smallest). Shift chain to outermost (largest) chainring in front.
  3. Test initial cable tension. Pedal a normal cadence and shift rear derailleur with one click on lever. Use care to only move lever one position. If derailleur moves one sprocket, tension is adequate.
  4. If derailleur fails to shift one sprocket, inner wire may be too slack. Turn barrel adjuster fully into derailleur body (or shift lever) then turn counter-clockwise two turns to allow for index adjustments. Loosen cable pinch bolt and gently pull on cable to remove slack. Tighten cable pinch bolt.
  5. If derailleur will not shift one sprocket after removing slack, return lever back to outermost sprocket position and increase cable tension by turning barrel adjuster counter-clockwise 1/4 turn and attempt shift again.
  6. Shift to second sprocket in rear. Pedal and increase inner wire tension by continuing to turn adjusting barrel counter-clockwise until a definite rattling is heard. Rattle is from chain scraping against next sprocket.
  7. Once a too-tight rattle is achieved, turn barrel adjuster 1/4 turn clockwise, to release cable tension, and pedal again. Listen and look for signs of scraping or rattling. Continue turning barrel adjuster 1/4 turn clockwise at a time until rattle disappears.
  8. Shift derailleur one sprocket inward at a time, listening for signs of rattle, indicating a too tight inner wire. Turn adjusting barrel 1/4 turn clockwise to eliminate rattle. Note: Do not attempt shift to largest rear sprocket while in largest front sprocket. This gear is normally not used and adjusting tension to this shift may compromise other commonly used gears.
  9. Shift to innermost (smallest) chainring and check gears again. If no rattling is present, index adjustment is done.


Front Derailleur Height and Rotational Angle

Usually, the bottom of the front derailleur's outer cage plate should clear the outer chainring by 1-2mm (about the thickness of a penny). The outer cage plate should also be parallel to the chainring. Some times both of these adjustments need to be modified to get good shifting.

Limit screw adjustments are similar to the rear: tighten limit screw just until too tight, and then loosen off by 1/4 turns until shifting is good.

Once limit screws and derailleur alignment has been set, indexing can be set if the bike has indexed shifters. Front shifting is indexed only if the shifter has 3 distinctive stops or clicks. If there are multiple clicks (or none), then the front shifting is not indexed.

Front indexing

  1. Shift chain to middle chainring in the front, and innermost (largest) rear sprocket.
  2. Gap between the inner cage plate and the chain should be as small as possible without rubbing the chain.
  3. To reduce gap, increase inner wire tension by turning barrel adjuster counter-clockwise. Adjusting barrel may be on frame or on shift lever. Check gap again.
  4. If chain is rubbing cage, turn barrel adjuster clockwise, or inward toward shifter body.
  5. If barrel adjuster is all the way in or out there will be no adjustment possible. In these cases reset the barrel. Shift to innermost chainring and loosen inner wire pinch bolt. Turn the barrel fully clockwise and back out about 2 full turns. Pull wire gently with fourth-hand tool and tighten pinch bolt. Begin adjustment of inner wire tension as above.

Test shift of front derailleur to all three front chain rings. If the derailleur rubs in the largest front chainring, double check H-limit screw and inner wire tension, which may be too loose. If chain is slow to shift to smallest chainring, double check L-limit screw and inner wire tension, which may be too tight.

Specific Skills

Repair Skills
Skill Content Reference
Front derailleur adjustments http://www.parktool.com/blog/repair-help/front-derailleur-adjustments
Rear derailleur hanger alignment http://www.parktool.com/blog/repair-help/rear-derailleur-hanger-alignment
Rear derailleur adjustment http://www.parktool.com/blog/repair-help/rear-derailler-adjustments-derailleur
Shift levers/shifters http://www.parktool.com/blog/repair-help/shift-levers-shifters
Housing http://www.parktool.com/blog/repair-help/housing-length

Drivetrain

Description

Demo chain cleaning, lube, and checking for wear

Details

(if there's attention span for this)

Content

Primary Content Instructor Notes

Drivetrains (sprockets, chainrings, and chains) last longer if they're kept clean! Dirt on a chain acts like a grinder, wearing away the chain and teeth on sprockets. Chains also make less noise and are more efficient (i.e. less work to pedal) if they're properly lubricated.

Use only bicycle chain lubricant for your chain. Avoid motor oils, and especially avoid solvents like WD-40. For dry, dusty environments, use "dry lube": these tend to wash off in the rain, but will keep your chain clean. For rainy environments, use a "wet lube", which lasts longer before washing off, but tends to attract dirt.

To apply, just drip lube onto each link while pedaling backwards.

Specific Skills

Repair Skills
Skill Content Reference
Pedals http://www.parktool.com/blog/repair-help/pedal-installation-and-removal-pw-3-pw-4-pw-5-hcw-16
Crank installation & removal http://www.parktool.com/blog/repair-help/crank-installation-and-removal-square-spindle-type
BMX cranks http://www.parktool.com/blog/repair-help/bmx-three-piece-crank-service
Cassette & freewheel removal http://www.parktool.com/blog/repair-help/cassette-and-freewheel-removal
Chain length http://www.parktool.com/blog/repair-help/chain-length-sizing
Chain installation http://www.parktool.com/blog/repair-help/chain-installation-derailleur-bikes
Chain tension for single-speed bikes http://www.parktool.com/blog/repair-help/chain-tension-on-one-speed-bikes

Free repair

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