silverz

I meant ChainRing.

New to biking...Bought a used Trek 1220 ZX and notice some jumping on the inner and mid ring. Looked and it looks like the teeth are worn down in a few locations.

The chainring says Shimano SG C-46, C-36 and C-24 for narrow chain only and it's 5 arm crank. Does anyone know of a good place to find a nice deal on replacements. Did a little researching and I think I'm looking for 110mm BCD for the mid and outer and 74mm BCD for the inner. Is that correct? Is brand important?

I might also get another chain for the bike...what type should I be looking for...Am I 9 or 10 speed...model no, etc. Sorry for all the stupid questions..like i said I'm new.

thanks.

joejack951

Post some pictures of the bike, the chainrings, and the rear cassette. Chances are, what you are seeing on the chainrings is normal and part of the design. The teeth on the rings are trimmed in certain areas to aid with shifting. Chainrings are not a common wear item so unless you have lots of miles on the bike and have never replaced your chain, the rings themselves are not likely the problem.

As for the actual cause of the jumping, what exactly is the chain doing? Is it falling off the chainrings?

silverz

If you look at the mid ring, it teeth look like they are worn or cut down at about 10 and 11 o'clock.

When I'm pedaling with the chain on the inner or mid ring it would like skip when I put force on the pedal climbing up hill. It's not falling off just feels like it's skipping.

AEO

it's a bit hard to see from your picture, but I would check your chain for wear.

get a 12" ruler, every pin will line up at exactly 1/2" on a new chain.
a worn chain will not, and if the pins go from 0 to 12-1/16~12-1/8 it needs to be replaced.

if you replace your chainrings and chain you should also replace the cassette in the rear.

cassette: looks like a 7 or 8, but I can't really see.
chain: match # with cassette, usually chains are rated for 1, 5/6/7, 7/8, 9 or 10 and you should use the one with the same number of gears as your cassette.
chainrings: sugino chainrings, 7/8/9, can always add thin spacers to get the spacing right for 9sp rings.

joejack951

Your chainrings look fine from what I can see. Unless they have a sharkfin-like shape, they do not need to be replaced. Your skipping problem is most likely a worn chain which in turn has worn out your cassette. Replace both at the same time using AEO's advice otherwise the problem will continue.

silverz

So you are counting the number of rows of teeth on the cassette to determine the speed. i.e. if i have 7 rows of teeth I have a 7 speed.

here is a close up picture of the teeth...showing off my mad paint skills




What is weird is that it runs smooth with the chain on the outer ring.


Thanks for all the help.

joejack951

When cassettes wear, they generally only get worn severely on the most used cogs. You probably use a few specific cogs and stay in the middle chain ring for the majority of your riding. Most likely, when you switch to the outer ring up front, you also change cogs in the back. Right?

silverz

I bought it used and have only taken it on one test ride.

After measuring the chain, they all seem to line up at 1/2" between pins.

joejack951

So which specific gear combinations slip when in the middle ring? All of them or just a few? Have you tried all combinations in the big ring?

DannoXYZ 

No, stretch the chain out and measure with a metal ruler. Put the end at the edge of one pin and go out to 12" and see where that final pin lines up. Its edge should be on the 12" mark as well. The distance between the edge of the pin and the 12" mark is the cumulative wear between 12 llnks. It should be 1/16" or less. If it's more, replace the chain.

Here's a photo:

https://bicycletutor.com/images/bike/...ar-400x280.jpg

This person started out with the ruler at the centre of the 1st pin. But it's hard to determine where in the middle of the pin the 12" mark falls. In this picture, it actually looks like 12" occurs before the centre of the pin; the chain is less worn than brand-new! That's why I prefer to line up on the edge of the pin.

silverz

I'll have to check that next time I take it out.