# How to replace a bike chain, derailleur or bottom bracket

Question: How do I replace a bike chain, derailleur or bottom bracket?
Updated: 2026-09-30
Canonical: https://suntekstore.com/guides/bike-drivetrain-parts/

## Short answer

Replace the worn part only after you confirm the bike’s mounting style, drivetrain size, and alignment points, because chain, derailleur, crank, and bottom bracket parts must match each other to shift and pedal correctly. For most riders, that means checking the chainring and crank first, correcting hanger alignment if shifting is off, and treating bottom bracket thread repair as a special job that needs the right dedicated tool.

## Start by identifying what is actually worn or damaged

A bike chain problem, a derailleur problem, and a bottom bracket problem can feel similar on the road, but they usually show up in different ways. Skipping this diagnosis is the fastest way to buy the wrong part.

If the bike skips under load, shifts poorly across multiple gears, or makes noise only in certain cogs, inspect the chain, chainring teeth, cable condition, and derailleur hanger alignment before assuming the derailleur itself is bad. If the crank feels loose, rough, or clicks once per pedal stroke, inspect the crank arms and bottom bracket area first.

A crank or chainring replacement only works if the new part matches the existing interface. For example, [Road Bike Chainring 130BCD](https://suntekstore.com/p/ST-54061072/) is a chainring listed with 130BCD, so it only makes sense if your crank spider uses that bolt circle. [Bike Crankset 32T Chainring](https://suntekstore.com/p/ST-54110442/) is a crankset with a 32T chainring, which is useful only if that tooth count and crank style fit your drivetrain and frame clearance.

If one crank arm is bent, stripped, or damaged, a single-arm replacement such as [Bike Crank Arm 127](https://suntekstore.com/p/ST-54087674/) may be enough, but only if its arm length and fitting style match what is already on the bike. If you are replacing both arms together, [Bicycle Crankset Set 165mm](https://suntekstore.com/p/ST-54097844/) is listed as a crankset set with 165mm arms, so check that 165mm is the length you want before ordering.

For a bottom bracket issue, first determine whether you need a new bottom bracket, a crank-side preload or cover tool, or actual thread repair. [Bottom Bracket Components Black](https://suntekstore.com/p/ST-54108368/) is a bottom bracket component set, while [Bicycle Pin Hook Wrench Set](https://suntekstore.com/p/ST-54110266/) is a pin hook wrench set meant for crank cover removal and related service, so they solve different problems. [Bike Bottom Bracket Tapping Tool](https://suntekstore.com/p/ST-54137325/) is specifically a bottom bracket tapping tool with 1.37 x 24 thread sizing, which is for chasing or repairing shell threads rather than routine part swaps.

## Choose by fit and interface, not by appearance

The safest way to shop for drivetrain parts is to match the connection points. On a derailleur repair, the hanger must be straight before you judge shifting. A tool like [Derailleur Hanger Alignment Gauge](https://suntekstore.com/p/ST-54061746/) helps check and correct derailleur hanger alignment so the derailleur can track the cogs properly again.

Cable drag is another common source of bad shifting that gets mistaken for a bad derailleur. [Bike Cable Housing](https://suntekstore.com/p/ST-54048426/) is cable housing listed in 5mm and 4mm sizes, so confirm which size your shifter or brake routing uses before replacing housing sections.

For chainring and chain area parts, tooth count and bolt pattern matter more than shape. [Bicycle Chain Guard](https://suntekstore.com/p/DCD-10001011942/) is a chain guard designed for 32-36 tooth chainrings, while [Bike Chainring Guard 42~44T](https://suntekstore.com/p/ST-54065792/) is a chainring guard for 42~44T rings. Those guards are not drivetrain repair parts by themselves, but they can be useful when you are rebuilding the crank area and want cleaner clothing clearance or chain protection.

Bottom bracket jobs need extra caution because there are several shell and spindle standards in the market. If your frame threads are damaged or painted over, [Bike Bottom Bracket Tapping Tool](https://suntekstore.com/p/ST-54137325/) may be relevant because it is listed with 1.37 x 24 thread sizing, but do not assume that thread matches your frame without checking the shell standard in the bike’s documentation or service notes. If your problem is worn bearings or loose play rather than damaged shell threads, a replacement assembly like [Bottom Bracket Components Black](https://suntekstore.com/p/ST-54108368/) may be the more appropriate part to evaluate.

When servicing the crank and bearing area, support tools matter too. [Hub Axle Tool Set](https://suntekstore.com/p/ST-66058946/) is a hub axle and bearing removal kit that the listing says is for bottom brackets as well, so review the included tool shapes in the product description and compare them with the bearing and cup style on your bike before relying on it for the whole job.

## How the chain, derailleur, crank, and bottom bracket work together

These parts act as a single system. The bottom bracket supports the crank spindle, the crank holds the chainring, the chain transfers power to the rear cogs, and the derailleur moves that chain sideways across gears. A problem at one point often shows up somewhere else.

For example, a worn chain can accelerate chainring wear, and a bent derailleur hanger can make a good derailleur shift badly. If you install a new derailleur but leave the hanger out of line, you may still get hesitation, ghost shifting, or chain noise. That is why an alignment tool such as [Derailleur Hanger Alignment Gauge](https://suntekstore.com/p/ST-54061746/) often matters as much as the derailleur itself.

Likewise, if you replace a bottom bracket or crank without matching crank length, chainring position, or mounting style, the chainline can move enough to hurt front or rear shifting. [Bicycle Crankset Set 165mm](https://suntekstore.com/p/ST-54097844/) gives you a known 165mm crank arm length to compare against your current setup, while [Road Bike Chainring 130BCD](https://suntekstore.com/p/ST-54061072/) gives a chainring option tied to a 130BCD crank spider.

A protective part can also affect the final setup. [Bicycle Chain Guard](https://suntekstore.com/p/DCD-10001011942/) covers chainrings in the 32-36 tooth range, and [Bike Chainring Guard 42~44T](https://suntekstore.com/p/ST-54065792/) covers 42~44T chainrings, so either one must match the ring size already on the bike. If you are replacing a crankset with [Bike Crankset 32T Chainring](https://suntekstore.com/p/ST-54110442/), check whether your current guard, front shifting clearance, and chainline still make sense after the swap.

## Common mistakes to avoid during replacement

The most common mistake is replacing parts before checking alignment and wear as a group. A new chain on badly worn teeth may skip, and a new derailleur on a bent hanger may still shift poorly.

Another mistake is assuming all bottom bracket service is the same. Thread repair, cup removal, bearing extraction, and crank preload adjustment are different operations. [Bike Bottom Bracket Tapping Tool](https://suntekstore.com/p/ST-54137325/) is for bottom bracket shell thread tapping with 1.37 x 24 sizing, [Bicycle Pin Hook Wrench Set](https://suntekstore.com/p/ST-54110266/) is for crank cover removal tasks, and [Hub Axle Tool Set](https://suntekstore.com/p/ST-66058946/) is a bearing and axle tool set that may help with some bottom bracket-related removal jobs, so choose the tool around the exact service step.

Do not choose crank or chainring parts by looks alone. [Bike Crank Arm 127](https://suntekstore.com/p/ST-54087674/) is a single crank arm, [Bike Crankset 32T Chainring](https://suntekstore.com/p/ST-54110442/) is a crankset with a 32T ring, and [Road Bike Chainring 130BCD](https://suntekstore.com/p/ST-54061072/) is a 130BCD chainring, so each one fits a different kind of replacement plan.

Finally, do not ignore cable condition when chasing derailleur issues. Housing contamination or friction can mimic a worn derailleur. If your routing is cracked, sticky, or rust-stained at the ends, refreshing it with [Bike Cable Housing](https://suntekstore.com/p/ST-54048426/) may be part of the fix, but make sure the 5mm or 4mm housing size matches your bike before cutting anything.

## A typical kit

1. [Derailleur Hanger Alignment Gauge](https://suntekstore.com/p/ST-54061746/): Use this to check and correct derailleur hanger alignment before blaming shifting problems on the derailleur itself.
2. [Bike Cable Housing](https://suntekstore.com/p/ST-54048426/): Replace old shifter housing when cable drag is causing hesitant or inconsistent gear changes.
3. [Bottom Bracket Components Black](https://suntekstore.com/p/ST-54108368/): Consider this when the bottom bracket assembly itself is worn and you have already confirmed the bike uses the right style.
4. [Bicycle Pin Hook Wrench Set](https://suntekstore.com/p/ST-54110266/): Use this for crank cover or preload-style service where a pin hook wrench is the correct interface.
5. [Bike Bottom Bracket Tapping Tool](https://suntekstore.com/p/ST-54137325/): Choose this only for shell thread repair or chasing when the frame uses the listed bottom bracket thread.
6. [Road Bike Chainring 130BCD](https://suntekstore.com/p/ST-54061072/): This is a chainring option for a crank that matches the listed 130BCD mounting pattern.

## FAQ

### How do I know whether bad shifting is the derailleur or just adjustment?

Start with the simple checks: cable friction, hanger alignment, and visible damage. A straight hanger checked with [Derailleur Hanger Alignment Gauge](https://suntekstore.com/p/ST-54061746/) and fresh housing such as [Bike Cable Housing](https://suntekstore.com/p/ST-54048426/) can solve many problems that seem like derailleur failure.

### Can I replace only one crank arm instead of the whole crankset?

Yes, if the damaged side is the only problem and the replacement matches the bike’s existing interface and arm length. [Bike Crank Arm 127](https://suntekstore.com/p/ST-54087674/) is a single crank arm option, while [Bicycle Crankset Set 165mm](https://suntekstore.com/p/ST-54097844/) is a full crankset set if both sides or the chainring area need replacement.

### What tool do I need for a bottom bracket replacement?

That depends on the exact task. [Bicycle Pin Hook Wrench Set](https://suntekstore.com/p/ST-54110266/) is for crank cover removal work, [Hub Axle Tool Set](https://suntekstore.com/p/ST-66058946/) may help with bearing or axle removal depending on the setup, and [Bike Bottom Bracket Tapping Tool](https://suntekstore.com/p/ST-54137325/) is specifically for bottom bracket shell thread repair with 1.37 x 24 sizing rather than ordinary parts removal.

### Should I replace the chainring when I replace a chain?

Only if the teeth are worn, hooked, or the new chain skips on them under load. If your crank uses that mounting pattern, [Road Bike Chainring 130BCD](https://suntekstore.com/p/ST-54061072/) is a chainring option to compare against your current part.

### Do I need a chain guard when replacing the crank area?

Not always, but it can be useful if you want cleaner clothing clearance or a little more protection around the chainring. [Bicycle Chain Guard](https://suntekstore.com/p/DCD-10001011942/) fits 32-36 tooth chainrings, while [Bike Chainring Guard 42~44T](https://suntekstore.com/p/ST-54065792/) is for 42~44T rings, so the guard must match your chainring size.

## Shop the list

Live price, availability and delivery window for every item mentioned above.

- [Derailleur Hanger Alignment Gauge](https://suntekstore.com/p/ST-54061746/): 40.49 USD, in stock, delivery 7-15 days, SKU ST-54061746 ([facts](https://suntekstore.com/p/ST-54061746.md), [buy](https://suntekstore.com/buy/ST-54061746?qty=1))
- [Bike Cable Housing](https://suntekstore.com/p/ST-54048426/): 12.99 USD, in stock, delivery 7-15 days, SKU ST-54048426 ([facts](https://suntekstore.com/p/ST-54048426.md), [buy](https://suntekstore.com/buy/ST-54048426?qty=1))
- [Bottom Bracket Components Black](https://suntekstore.com/p/ST-54108368/): 28.09 USD, in stock, delivery 7-15 days, SKU ST-54108368 ([facts](https://suntekstore.com/p/ST-54108368.md), [buy](https://suntekstore.com/buy/ST-54108368?qty=1))
- [Bicycle Pin Hook Wrench Set](https://suntekstore.com/p/ST-54110266/): 18.19 USD, in stock, delivery 7-15 days, SKU ST-54110266 ([facts](https://suntekstore.com/p/ST-54110266.md), [buy](https://suntekstore.com/buy/ST-54110266?qty=1))
- [Bike Bottom Bracket Tapping Tool](https://suntekstore.com/p/ST-54137325/): 82.79 USD, in stock, delivery 7-15 days, SKU ST-54137325 ([facts](https://suntekstore.com/p/ST-54137325.md), [buy](https://suntekstore.com/buy/ST-54137325?qty=1))
- [Road Bike Chainring 130BCD](https://suntekstore.com/p/ST-54061072/): 44.19 USD, in stock, delivery 7-15 days, SKU ST-54061072 ([facts](https://suntekstore.com/p/ST-54061072.md), [buy](https://suntekstore.com/buy/ST-54061072?qty=1))
- [Bike Crank Arm 127](https://suntekstore.com/p/ST-54087674/): 22.24 USD, in stock, delivery 7-15 days, SKU ST-54087674 ([facts](https://suntekstore.com/p/ST-54087674.md), [buy](https://suntekstore.com/buy/ST-54087674?qty=1))
- [Bicycle Crankset Set 165mm](https://suntekstore.com/p/ST-54097844/): 27.99 USD, in stock, delivery 7-15 days, SKU ST-54097844 ([facts](https://suntekstore.com/p/ST-54097844.md), [buy](https://suntekstore.com/buy/ST-54097844?qty=1))
- [Hub Axle Tool Set](https://suntekstore.com/p/ST-66058946/): 194.69 USD, in stock, delivery 7-15 days, SKU ST-66058946 ([facts](https://suntekstore.com/p/ST-66058946.md), [buy](https://suntekstore.com/buy/ST-66058946?qty=1))
- [Bicycle Chain Guard](https://suntekstore.com/p/DCD-10001011942/): 9.59 USD, in stock, delivery 11-21 days, SKU DCD-10001011942 ([facts](https://suntekstore.com/p/DCD-10001011942.md), [buy](https://suntekstore.com/buy/DCD-10001011942?qty=1))
- [Bike Chainring Guard 42~44T](https://suntekstore.com/p/ST-54065792/): 7.59 USD, in stock, delivery 7-15 days, SKU ST-54065792 ([facts](https://suntekstore.com/p/ST-54065792.md), [buy](https://suntekstore.com/buy/ST-54065792?qty=1))
- [Bike Crankset 32T Chainring](https://suntekstore.com/p/ST-54110442/): 23.39 USD, in stock, delivery 7-15 days, SKU ST-54110442 ([facts](https://suntekstore.com/p/ST-54110442.md), [buy](https://suntekstore.com/buy/ST-54110442?qty=1))

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