E-Bike Parts

Cranksets

Cranks, chainrings and bottom brackets — including PAS-compatible options.

Cranks, chainrings and bottom brackets take a beating on e-bikes. Chainrings wear to a shark-fin shape, crank arms get stripped where the pedal threads in, and bottom bracket bearings develop play. On hub-drive bikes these are mostly standard bike parts with one wrinkle: the pedal-assist magnet ring sits on the crank spindle and has to clear the new parts. On mid-drive bikes, the crank and chainring attach to the motor and are usually motor-specific. The good news is that the wear parts are inexpensive and the tools (a crank puller and a bottom bracket tool) are cheap and reusable.

Start by identifying your crank interface. Square-taper spindles are the norm on hub-drive e-bikes and budget bikes; other standards (ISIS, Octalink, two-piece external-bearing cranks) appear on nicer bikes. Crank arm length (commonly 170 or 175mm) and chainring size and bolt circle (BCD) determine what chainrings fit. On a hub-drive bike with a single chainring, a narrow-wide ring helps keep the chain on, and a chainguard keeps pants clean.

Bottom brackets are sized by shell width (68 or 73mm on most bikes, wider on fat bikes) and thread standard, and square-taper units also by spindle length, which sets chainline and clearance for the pedal-assist ring. Replace like-for-like unless you understand the chainline implications. Confirm your interface, shell width and spindle length on your bike before ordering, and on mid-drives, buy parts made for your motor model. Crank length is also worth a thought: shorter cranks reduce pedal strikes on small-wheel and low-bottom-bracket e-bikes and are easier on knees for casual riders.

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Cranksets

170 mm Square Taper Single Crankset, 44T with Chainguard (generic)

The typical hub-motor e-bike has a single front chainring on a square-taper crankset, and when a crank arm strips or the chainring wears hooked, the replacement is a generic 170 mm alloy crankset with a 44T or 46T ring and a plastic chainguard. These are sold by many sellers and are functionally interchangeable. The important checks are square-taper bottom bracket (not Octalink or Hollowtech), crank length, and chainring size; keep the same tooth count to preserve your gearing. A square-taper crank puller is needed for removal.

Best for: Replacing a stripped crank arm or worn chainring on a hub-motor e-bike · Bikes with a square-taper bottom bracket · Budget repairs

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Cranksets

Shimano BB-UN300 Square Taper Bottom Bracket

The UN300 is the sealed-cartridge square-taper bottom bracket Shimano sells as the successor to the long-running UN55 and UN26, and it is the right replacement for the creaking, gritty bottom bracket on most hub-motor e-bikes. It comes in several shell widths (68 and 73 mm are common) and spindle lengths, so you need to measure or read the old unit. Installation needs a splined bottom-bracket tool. Once in, it is a fit-and-forget part — which is exactly what you want on a commuter that gets ridden in the rain.

Best for: Fixing a creaking or loose bottom bracket on a square-taper bike · Pairing with a new square-taper crankset · Hub-motor e-bikes with standard threaded shells

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Sold on Amazon

How to choose cranksets

Crank interface

Square-taper (JIS is typical), ISIS, Octalink, or two-piece external. Match your bottom bracket or replace both together.

Crank length

170 or 175mm are common; shorter cranks can reduce pedal strikes on small-wheel and low-bottom-bracket bikes.

Chainring size and BCD

Match the bolt circle (104, 110 or 130mm BCD are common) and count bolts. Ring size sets your gearing; tooth count is stamped on the ring.

Pedal-assist clearance

The PAS magnet ring needs room on the spindle; a crank or ring with a different offset can hit the sensor.

Bottom bracket shell and spindle

Measure shell width and note the thread standard and spindle length for square-taper; changes move the chainline.

Compatibility notes

Crank and bottom bracket interfaces must match; confirm on your bike before buying either.
Chainring BCD and bolt count must match the crank spider.
On hub-drive e-bikes, confirm the pedal-assist magnet ring still fits and aligns with the sensor after any crank or bottom bracket change.
Mid-drive cranks and chainrings are motor-model specific; see the mid-drive category.

Installation considerations

Remove the crank with a crank puller and note how the pedal-assist ring sits before disturbing it.
Grease square-taper spindles lightly (or follow the maker's advice) and torque crank bolts firmly to spec.
Check chainline and chainring bolt torque, then spin the cranks and verify the PAS sensor still triggers.
Left pedal is reverse threaded; do not force it the wrong way.

Maintenance tips

Retorque crank bolts after the first rides; loose square-taper cranks ruin the arm quickly.
Replace the chainring when teeth hook or the chain skips with a new chain.
A creak under load is often a dry crank or bottom bracket; clean, grease and retorque before replacing.

Frequently asked questions

What kind of crank does my e-bike have?

Pull the crank bolt cover: a square hole with a single bolt is square-taper; a round splined hole is ISIS or Octalink; a large hollow spindle passing through is a two-piece crank. Most hub-drive e-bikes are square-taper.

Can I change my chainring size?

Yes if the new ring matches your BCD and bolt count and the chain length and derailleur capacity can handle it. A smaller ring helps climbing; a larger one raises top pedaling speed.

Will a new crank fit with my pedal-assist sensor?

Usually, but the PAS magnet ring sits on the spindle and a different crank offset can hit the sensor. Check clearance before final tightening.

Why does my crank creak?

Loose crank bolts, a dry spindle interface, a worn bottom bracket, or loose pedals. Tighten and grease before assuming the bottom bracket is bad.

Do I need a special crank for a mid-drive?

Yes; mid-drive motors have their own crank interface and chainring mount, so buy parts listed for your motor model.