Author Topic: chain ring sizing  (Read 4842 times)

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Offline PeteJack

chain ring sizing
« on: November 05, 2014, 11:48:33 am »
A friend of mine who is an expert(!) was appalled that the front triple on my 520 was 51-38-24. He claimed that you're not supposed to have more than a 20T gap between the largest and smallest rings. Does he have something?

the only odd thing I have had happen was when I got to the top of a longish hill and shifted up from the granny perhaps a bit too soon and the Quicklink came undone. It was all twisted when I checked it so I replaced it with a spare and was on my way. Other than that strange incident I've rode any thousands of trouble free miles with this arrangement.

Offline dkoloko

Re: chain ring sizing
« Reply #1 on: November 05, 2014, 12:32:48 pm »
Answer no. Ran 50-45-24 for many years, no problems. Your chain problem is another matter.

Offline RussSeaton

Re: chain ring sizing
« Reply #2 on: November 05, 2014, 01:51:40 pm »
Your chainrings sizes are fine.  On my 1991 Trek 520 I used 50-45-24 chainrings.  Then 48-45-24 rings.  Current bike has 44-33-20 rings.  Shifting to and from the inner chainring has always worked perfectly using either triple or double front derailleurs.  Barend or STI shifters.

http://bike.shimano.com/content/sac-bike/en/home/components1/road/105/fd-5703-b-l.html
Above is a link to the Shimano 105 triple front derailleur.  It lists 20 teeth as the maximum capacity.  Difference between large and small chainrings.  But this number is very conservative.  And fictional.  You can exceed the 20 teeth difference and be just fine.

As for your quicklink coming undone.  Unsure.  Perhaps you did not have it installed correctly and it took until then under those exact circumstances to come undone.  Some of them click together.  Others just fit together with nothing clicking to hold them together.

Offline DaveB

Re: chain ring sizing
« Reply #3 on: November 05, 2014, 06:27:30 pm »
Agree that your "expert" need more and better information.  I've had several bikes geared 52/42/26 and 53/42/26 and 50/39/26 and they all shift well and reliably.

Edit to add an additional comment:  There is a possible problem with a huge chainring difference.  The top run of the chain can drag on the tail of the front drailleur in the small small combinations so you won't be able to use them, at least not quietly.   No loss as there is no reason to use the granny ring with the smallest few cogs anyway.
« Last Edit: November 05, 2014, 10:40:27 pm by DaveB »

Offline PeteJack

Re: chain ring sizing
« Reply #4 on: November 06, 2014, 09:13:33 am »
I've come up with an explanation for the Quicklink separating. The derailer cage pushed the left side of the Quicklink backward and the ramps on right side pushed it forwards thus opening up the QL, the sideways push to move to the middle ring pulled it apart. I think not shifting quickly enough gave it time to separate. It hasn't happened since (about 2000 miles). Probably nothing directly to do with chain ring sizes but the size difference does mean the chain is quite slack on the granny. I found out the hard way not to do anything about that by shortening the chain.
« Last Edit: November 06, 2014, 09:15:34 am by PeteJack »

Offline Old Guy New Hobby

Re: chain ring sizing
« Reply #5 on: November 06, 2014, 09:44:38 am »
About the quick link - I used to lubricate my chain with melted paraffin mixed with graphite. I removed and replaced the chain each time I lubricated it. I found that as the quick link was used, it gradually became more likely to come apart while riding. Replacing an unreliable quick link with a new one would solve the problem. I used to keep a spare quick link in my tool kit. When I started touring, melting paraffin was no longer practical and I switched to Bloeshield T-9 chain lube. Now I don't remove my chain nearly as often, and the quick links last the life of the chain. I still have several spare links that are years old that I will probably never use. You don't mention how many times you have removed your chain. If it's been taken off and on several times, this might be the issue. FYI, I use SRAM quick links.

Offline PeteJack

Re: chain ring sizing
« Reply #6 on: November 06, 2014, 11:54:31 am »

Quote
You don't mention how many times you have removed your chain.
The chain had about 1000 touring miles on it and had never been removed. Maybe it's QC on the QLs (!) but sometimes they separate easily and other times they can be a bear to get apart. I only separate when replacing a chain, never to clean a chain.