Generic BBSHD Steel Chainring

Steel is harder than aluminium, so each tooth holds its shape longer under the same abuse. Pile on miles in bad weather and that alone justifies it. A cargo bike carrying kids up a long hill every morning, or a fat bike ridden through slush and road salt all winter, wears a drivetrain far faster than a summer trail bike.

• Longer life under constant motor torque and dirty chains.
• Small sizes only in steel, from 32T to 38T, which suit climbing and cargo.
• Anti-drop teeth keep the chain seated over rough ground without a front derailleur.
• Heavier than an aluminium ring of the same size; the trade for durability.

The maker lists fit for the BBSHD, BBS03, G320, M615 and M625, all 1000W systems. BBS03 is another name for the BBSHD, and M615 and M625 are Bafang's newer model codes for the same family, with M625 commonly tied to wide-shell fat-bike versions. It does not fit the smaller BBS01 or BBS02.

A few rules of thumb help pick between them:

• Cargo, towing, winter: the steel 32–38T ring.
• Steep trails on a regular frame: the 36T 13mm offset ring for lower gearing and a straighter chain.
• Mixed commuting: the aluminium 40T or 42T.
• Fast road riding with lots of throttle: a large ring from the 40–52T range.

Because the versions share one name, read the tooth count and material on the part you receive before fitting it. A steel ring and an aluminium ring of similar size look alike in black, and the offset is easy to miss until the chain starts rubbing. Hold the new ring against the old one on the bench: the difference in tooth position tells you how far the chain will move.

The 42T offset-correction ring is the chainline fix for riders happy with the stock gearing but tired of chain rub in the big cogs. Offset and chainline on different frame widths are worked through in the BBSHD chainring guide.

1. Switch the battery off and unplug it. A bumped throttle with your fingers in the chainring is a bad day.
2. Remove the drive-side crank arm with a crank puller.
3. Unbolt the old ring and note any spacers or covers, and their order.
4. Clean the mounting face of grit and old thread-locker.
5. Fit the new ring, tightening the bolts gradually in a cross pattern with a drop of medium thread-locker.
6. Refit the crank arm, then spin the cranks and check the ring runs true and clears the chainstay.

Changing tooth count changes chain length. Dropping from a 46T stock ring to 36T frees up chain; going to 52T needs more. Re-size the chain so the rear derailleur has correct wrap in the biggest and smallest cogs.

• Moving from 46T to 36T, remove chain links so the derailleur is not slack in the small cog.
• Moving up to a 48T–52T ring, check the largest cog still shifts without stretching the derailleur.
• Fit a new chain with a new ring if the old one has stretched.

If the motor is coming off anyway, use the BBSHD install guide for the lockring, the bottom bracket fit and the torque on the main mounting nut. A speed sensor re-check is worth doing too, since the magnet sometimes gets knocked during rear-wheel work.

• This steel ring: 32–38T, anti-drop teeth, wear resistance for cargo and fat bikes.
• CHAOZHU: 6061-T6 aluminium, a 42T with a deep 20.5mm offset for regular frames, or an 8mm-offset 32–38T for fat bikes.
• Powallon 42T: aluminium with an integrated guard for commuters in street clothes.

Pick the steel ring for a hard-worked bike: heavy cargo, towing, winter riding, fat tires on soft ground. It accepts a dirty chain better and lasts longer between replacements. Pick an aluminium offset ring if your chain rubs or drops in the big cogs on a 68–73mm frame, since fixing chainline also reduces wear.

Read the motor code on the housing first: it should say BBSHD, BBS03, M615 or M625, not a BBS01 or BBS02. Choose tooth count from the gearing you want, and allow for re-sizing the chain. If you pick one of the aluminium versions, check the offset against your frame and the chain speed against your drivetrain.

Chain care decides ring life more than material does. A clean, lubed chain replaced before it stretches will make a steel ring last a long time, and even an aluminium one last well. The torque figures behind all of this come from the BBSHD 1000W guide.