[Doug B]

I've got a Shimano 105 Crank with a 50 tooth chainring installed. With about 14000 miles, the teeth are worn down a bit, and I'm gathering parts to perform some bike overhaul maintenance once the snow flies this winter.

Nope, I'm not having any shifting problems. No problems at all, actually.

The only markings I can find on the existing chainring are: SHIMANO 50F

I can measure the bolt circle diameter to find out if it's 110 or 130. I understand that - but haven't done it yet. I can count teeth.

Are there any other things I should consider when looking for a replacement chain ring?

A quick internet search leaves me with pricing for a 50 tooth Shimano Chain ring that varies from $25 to $125.

Will any 50 tooth ring with the correct bolt circle diameter work?


How's this? Shimano Ultegra 6650 Compact Chainring > S > Shimano | Jenson USA

 

[skinewmexico]

Hopefully the entire drivetrain isn't so worn that you have to replace it all. Probably need a new chain and cassette if the chainring is worn that much.

 

[duriel]

If it is a 50 tooth, then the bolt circle is 110. You can't get a 50 with a 130, the bolt circle is too big.
Usually your chain & cassette goes bad way before the rings.

 

[Blue CheeseHead]

The link you provided is for a 34t chainring which is a fine replacement for your small ring.

If your shifting is fine and the chain is not skipping, why are you replacing your chainring(s)? 14,000 miles is not that many unless you have never changed your chain.

 

[MMsRepBike]

If you want new chainrings, these are really nice:

https://www.praxiscycles.com/product/compact-road-sets/

 

[rm -rf]

Are you sure the chainrings are worn out? They come from the factory with differently shaped teeth to make shifting easier. After 14,000 miles, they probably show wear on the flat sides of the teeth, but are likely still good.

See this thread on another forum for some useful pictures and a discussion about how much wear to tolerate.

A badly worn chainring allows the chain to ride up on the teeth. Here's an extreme example:
View attachment 309884

 

[JCavilia]

If it is a 50 tooth, then the bolt circle is 110. You can't get a 50 with a 130, the bolt circle is too big.
Usually your chain & cassette goes bad way before the rings.

Your second statement is correct. Your first is not. A 130 bcd spider can handle an inner ring as small as 38 teeth, so it can't be "too big" for a 50. There are lots of 50-tooth 130 rings.

It is generally true that a 50-tooth ring is part of a "compact" crankset, with an inner ring of 34 or 36, so chances are that's what he has. Easy enough to find out.

 

[Jay Strongbow]

Will any 50 tooth ring with the correct bolt circle diameter work?

No. 11 speed and 10 speed are different for Shimano.

 

[duriel]

dah... if it is a 50T I assumed that it was paired with a 34 or 36. The 130mm is too big for a 34. Woops.

 

[Doug B]

My details:
10 speed
110mm bolt circle - I measured it last night
50/34 compact
Shimano 105 crank arms

I understand the crazy shapes and cuts on the teeth that aid shifting. I've "mapped" them out - there is a pattern to the shapes that repeats about every 60 degrees.

The teeth on my 50 tooth are getting to be "shark tooth" in shape. But looking at some of the photos and reading thru the other forum thread, and considering that I'm not experiencing any chain jumping problems, I may not do anything with the chain ring at this time. I think I'll wait until I begin to experience shifting or other problems.

I replace my chain about every 2000 miles. I clean and oil the chain about every 150 miles.

My cassette was new about 6000 miles ago. It honestly looks as good as it did when it was new.

I still have a difficult time understanding how a (somewhat hardened) steel cassette gear will wear faster than an aluminum (even anodized 7075 aluminum) chain ring, even considering the cassette is experiencing two or three times the revolutions as the chain ring. Many of the parts I deal with at work are made from 7075. I would never consider using it for a "wear" component without a hard anodize and a baked on dry-film lubricant finish. Even then... I would want the dry film lube reapplied every so often.


The reason I ask all of this...
I like to have "spare parts" on hand, when I can. When it's time for maintenance, it is very frustrating to either have to wait to receive an ordered part, or discover the LBS is closed and/or doesn't have the part in stock.

My wife is bugging me for an xmas list (yeah - it's ten weeks away folks) and I figured why not give her a list of things I'll eventually use. I tell her not to buy me anything. But, I've come to realize that when I tell her "nothing", she buys me a bunch of junk that I end up throwing away.


So, I guess, any 50 tooth ring, with a 110 bolt circle is basically acceptable.

 

[ericm979]

Check the 34t too. It's hiding behind the 50t so it's harder to notice when it is worn.

Some chainrings will look better on your crank than others. Both the color and the shape matter. Some chainrings shift better than others, and some wear better.

Shimano chainrings are good shifting and wear well, and would match your crank.

 

[GKSki]

Jay when you said Shimano 10 and 11 sp were different, you meant the new 11sp spider correct?

 

[Jay Strongbow]

Jay when you said Shimano 10 and 11 sp were different, you meant the new 11sp spider correct?

that's right.

 

[GKSki]

Thanks. I know when I replaced a 10sp Shimano crankset with the 11sp version, I had no problems with it working with the 10sp chain and drive train.

Not sure what the BCD is for these new 4-spider chainrings.

 

[Jay Strongbow]

Thanks. I know when I replaced a 10sp Shimano crankset with the 11sp version, I had no problems with it working with the 10sp chain and drive train.

....and thank you. I'm actually contemplating getting an 11 speed crank (because I don't see any 10 speed DA still for sale) to use with a 10 DA group so it's good to hear from someone who had it work okay.
I heard it's not problem elsewhere also.....but the other way around wouldn't be a good idea from what I hear.

 

[Blue CheeseHead]

Not sure what the BCD is for these new 4-spider chainrings.

BDC for the 4 bolt spider is irrelevant as they only make one bolt pattern. Standard, mid-compact and compact chainrings all fit it.

 

[Blue CheeseHead]

....and thank you. I'm actually contemplating getting an 11 speed crank (because I don't see any 10 speed DA still for sale) to use with a 10 DA group so it's good to hear from someone who had it work okay.
I heard it's not problem elsewhere also.....but the other way around wouldn't be a good idea from what I hear.

Shimano & SRAM 10sp & 11sp cranksets are interchangable in either direction. The distance between plates on chain are the same, but the plates are thinner on the 11sp.