Cranksets and chain rings for newbies

@lordofthemark 178811 wrote:

I have been told by the good folks at Phoenix that I probably need a new crankset/chain rings.

1. To tell if the chain rings are worn out, I check the teeth right? I could post some pics here for your opinions.

Put the chain on the outer chainring, put the pedals in the 6 o’clock and 12 o’clock position. Grab a single outer link of the chain at the 3 o’clock position and pull away from the chainring. If you can see more than 2 or 3mm between the top of the tooth (on a non-“shaped” or intentionally truncated tooth) and the bottom of the outer link, that chainring should probably be replaced. Repeat the same process on other chainrings (middle, granny).

2. In theory I don’t have to replace all the chain rings at once right? I could only replace the worn ones.

I’d recommend replacing the middle and outer at the same time. the inner usually doesn’t see enough wear unless the drivetrain is completely filthy.

3. Some people say just replace the whole crankset its more economical. What are the pluses and minuses?

I’m restating, but in your specific case I’d recommend replacing the crankset. Pluses: it’s super cheap, shifts great, and is pretty easy. minuses: it seems wasteful, and will likely upset the spirit of Sheldon Brown. If you were asking about old 9 speed Dura Ace, I’d suggest just replacing the chainrings.

4. Assuming its reasonable to just replace the chain rings, how do I tell if the other parts (that is just the crank arms, correct?) are worn out or need replacement?

You will likely need to replace chain, cassette, and chainrings at the same. If you keep using an old cassette, it will prematurely wear out the new chain, which will prematurely wear out the new chain rings. You will also need to inspect the pulley wheels in the rear derailleur for worn teeth, too.

5. Are there issues with sizing? Will any crankset or chain rings fit any bike? (oops I just saw wiki has something on this, but not clear if I need to worry about it)

The wiki (and google) cover BCD and chainring spacing for 6, 7, 8, 9, 10, 11/12 spd pretty well. It would take me 3 days to type out all the idiosyncrasies of BCD permutations and weird crank/bottom bracket setups. Be glad you have one of the most common setups, i.e., JIS square taper, threaded BB, 74-110BCD (as best as I can tell by looking at pictures) 5-arm triple.

6. Following on from 5, I see chain rings offered cheap on the DC bike marketplace. What do I need to know in terms of sizing, etc to make sure they are right for my bike?

See above re: sizing/specifications – I don’t see a problem getting chainrings used for cheap off of DC Used, but you have to know what to look for on a bare chainring as far as wear characteristics to be sure you’re not getting an already worn chainring. I’d prefer new take-off, or BNIB over “used, only 500 miles”.

7. I know this came up on the other thread, but is replacing the chain rings or the crankset myself difficult? What do I need to know?

The first time you remove a crank arm, you’re going to be surprised at the smell of the grease on the spindle.

1) remove both pedals
2) remove both crank bolts
3) remove crank arms using appropriate crank removal tool
4) install new crank arms, tighten to 30 ft/lbs
5) install pedals
6) adjust upper and lower limit screws on front derailleur
7) adjust cable tension on front derailleur

answers bolded above.