What a Gear Ratio Actually Means for Your Knees

Comparisons of bicycle gearing usually pick a winner. This one picks the circumstances, which is more useful.

What the tooth counts are telling you

A gear ratio is simply the front chainring tooth count divided by the rear sprocket tooth count, and everything else follows from that division. A ratio of two means the rear wheel turns twice for every full revolution of the pedals, so each pedal stroke covers more ground.

The same ratio also means every unit of forward push has to come from a shorter, harder movement at the pedal itself. Multiply the ratio by the wheel circumference and you get development, the distance travelled per pedal revolution, which is the number that actually matters. Two bikes with wildly different component names can produce identical development, which is why comparing gear counts between machines tells you almost nothing.

Force, cadence and the joint in the middle

Your legs deliver a roughly fixed amount of power, and gearing decides whether that power arrives as many light strokes or few heavy ones. Pushing a high gear slowly means high peak force at the pedal, and that force is resisted largely by the muscles crossing the knee.

The bit that actually matters: spinning a lower gear faster produces the same forward speed with less force per stroke, spreading the work across more repetitions. Cycling researchers have generally found that riders self-select higher cadences than pure metabolic efficiency would suggest, which is usually read as the body protecting the joints. If your knees ache after a ride and your legs do not, the usual culprit is gearing that is too tall for the terrain.

Why the same hill feels different on two bikes

A hill does not get steeper, but the lowest gear available decides whether you can climb it seated at a comfortable cadence. Run out of low gears and you have only two options left, standing on the pedals or grinding slowly at high force. Standing recruits your body weight and works briefly, but it raises your heart rate sharply and is hard to sustain for a long climb.

Grinding is the option that hurts later, because the knee is absorbing repeated high loads through a small range of movement. A bike with a genuinely low bottom gear turns a hill from an event into a slower section of the same ride.

Range beats gear count

Marketing counts gears by multiplying chainrings by sprockets, which produces impressive numbers and several duplicated or unusable combinations. What you actually use is the spread between the lowest and highest development, and that spread is what determines where the bike is comfortable.

A machine with eight well-spaced gears covering a wide range is more useful in a hilly city than twenty-two clustered narrowly. Wide ranges come with a cost, since bigger jumps between adjacent gears make it harder to hold an exact cadence on rolling ground.

For transport riding that trade is almost always worth taking, because being able to climb matters more than a perfectly even step.

Finding a cadence you can hold

Most riders settle somewhere in the region of seventy to ninety pedal revolutions a minute on flat ground once they stop thinking about it. That range is a description of what people do rather than a rule, and trained riders, heavier riders and older knees all sit differently within it. Count your pedal strokes for fifteen seconds and multiply by four, which is enough precision to tell whether you are grinding or spinning.

If you cannot hold a conversation your effort is too high, and if your knees are the first thing to complain your gear is too tall. Shift before the gradient rather than during it, because a chain under heavy load resists moving and the shift arrives late and rough.

Frames, sizes and riding positions vary enormously; borrow before you buy wherever you can.

Gearing a bike for a city

City riding is stop-start, so the gears you use most are the ones that get you moving again from a standing start. That argues for a lower overall range than a bike shop demonstration ride on flat ground would suggest is necessary. Carrying luggage changes the calculation again, since a loaded rack effectively makes every gradient steeper without changing anything about the bike.

Mid-traffic, most transport bikes can be given a lower bottom gear cheaply by changing the rear sprockets or the chainring rather than the whole system. Ask a mechanic what the current lowest development is before buying anything, because the answer sometimes reveals the bike was never geared for hills.

Side by side

The takeaway

Gears exist to keep your cadence steady while the road changes underneath you.

Most of riding well is being boring and predictable to everyone else on the road.