Maintenance
Pedal Threads Are the Ones That Strip First
Pedals thread directly into aluminum crank arms under constant load, and one of them is reverse-threaded, which is why cross-threading a crank is a common expensive mistake.
Of all the threaded connections on a bicycle, the pedal into the crank arm is the one most often destroyed by an owner. The reasons are the reverse thread on one side and the material it threads into.
One side is left-hand threaded on purpose
The right pedal has a conventional right-hand thread and the left pedal has a left-hand thread, so it tightens counterclockwise.
The reason is a phenomenon called precession, in which the pedal axle rolls around the inside of the threaded hole as the bearing turns under load.
That rolling motion would gradually unscrew a conventional thread on the left side, so the thread direction is reversed to make riding tighten it instead.
Cross-threading happens in the first two turns
A rider who forgets the reverse thread applies force in the wrong direction, and aluminum crank threads yield before a steel pedal axle does.
Damage is done almost immediately, and once the first threads are deformed they guide the axle further off axis with each turn.
The correct method is to start every pedal by hand until it turns freely for several rotations, and to stop entirely at any resistance.
The materials are mismatched by design
Pedal axles are steel and crank arms are usually aluminum, so the softer material is the one carrying the threads.
Dissimilar metals in contact also promote galvanic corrosion in the presence of moisture, which can seize a pedal into a crank over years.
Grease or anti-seize on the threads addresses both problems, easing installation and preventing the two metals from bonding.
Removal confuses people for the same reason
Both pedals loosen toward the rear of the bike, which is the simplest way to remember the directions without thinking about handedness.
Seized pedals need leverage applied in that direction, and a long wrench with the crank braced is safer than sudden force with a short one.
Heat, penetrating fluid, and patience are the usual approach when a pedal will not move, since forcing it risks the crank rather than the pedal.
When threads are already gone
A stripped crank arm can sometimes be repaired with a threaded insert installed by a shop, which restores usable threads in the existing arm.
Whether that is appropriate depends on how much material remains and on the crank's construction, which is a judgment for a mechanic rather than a driveway.
The alternative is a replacement crank arm, which is why the two minutes spent starting a pedal by hand is the best-value maintenance habit available.
Questions readers ask
My steering feels notchy in the straight-ahead position. What is that?
An indented headset bearing race, usually caused by riding with a loose headset. The notch cannot be polished out, so the bearing needs replacing, and the adjustment needs correcting afterwards.
How long should bearings last?
It depends far more on water and grit than on distance. A bike with mudguards and dry storage can go years; one ridden through salted winters without guards may need attention annually.
