I am replacing my chain, cassette and chainrings and am unsure which model chainrings to buy. I have already bought the chain (9-speed Shimano Ultegra). My current cassette, which I will be replacing, is an 11/26 9-speed and I have a 34/50 in the front (compact, can't tell if it is Tiagra or 105, but probably not Ultegra since I don't remember it being that expensive).

I found the following 34-tooth that specifies it is for a compact:

https://www.bikesomewhere.com/bikesom.../18/5286/34643

and here is a 50T chainring

https://www.bikesomewhere.com/bikesom.../18/5286/34353

The 50T, however, is for a double, not specifically for a compact. So my questions are:

1. Is the 50T compatible even though it says it is for a double?

2. Will these 105 chainrings be compatible with my current crank if the crank is a Tiagra (and again, I can't seem to figure out if it is or not).

Any info is appreciated.

You can identify your crankset using the model number on the inboard side of the crank at the pedal hole (4500-series are Tiagra, 5600-series are 105), or by the fact that the 105 cranks are hollow, whereas the Tiagras are just channeled on the inboard side. The 105s also say "105" on them, and the Tiagras say "Tiagra."

The 50-tooth chainring in your second link will not work on a compact because it has the un-compact 130mm bolt-circle diameter. You need 110mm BCD.

Thanks mech. I know that the inboard side of the crank is channeled, so I'm guessing it's a Tiagra (I will look again when I go home tonight to see if it is obvious as you suggest). Assuming that it is a Tiagra crank, can I install 105 chainrings on it?

I was able to find a compact 50T, so that issue is now resolved.

If the Bolt Hole Diameters (BCDs) are the same, then you can interchange them (with some caveats). When you price new ones, though, you might find that it's almost as cheap to replace the crank.



Now for the $64,000 question: Why are you changing the 'rings? They wear out a lot slower than the other components.

The chain is very stretched and it appears to have damaged the chainrings (as well as the cassette). I'll try to upload some photos tomorrow showing the damage--I'm open to second opinions.

Slap on the new chain and (assuming it's installed correctly). If you start skipping in the front/rear. They're toast. You might also want to quanity "very stretched".

Yeah, especially with the way Shimano cuts teeth on the 'rings, it's quite difficult to gauge wear with the Mk. I Eyeball. It's likely that the cassette is toast (again, quantify "stretch"), but leave the 'rings until you get the others replaced and have an actual problem.