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Change only the inner chainring of dual setup

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Change only the inner chainring of dual setup

Old 01-30-19, 09:17 PM
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Change only the inner chainring of dual setup

I ride a 10-speed, dual chainrings front, 5 speed freewheel rear. Front setup is Shimano 600, 40T and 52T alloy chainrings. I ride almost exclusively on the small chainring, I noticed that the fronts of the teeth are starting to get a little concave from the chain, not bad yet, but I have flipped it over so the good side of the teeth is now facing forward.
I was idly looking for replacements, if I replace it I would prefer to go to 42T, but I found a site that said the outer and inner rings they sold were designed to be a matched pair as far as tooth count and tooth clocking, that a non-mated inner would affect the shifting.
Is there something to that? Is there some sort of synchronization between the clocking of outer teeth and inner teeth that would be thrown off if I went to a different inner with different tooth number? It seems a little hard to believe, at some point in the crank rotation you will have teeth aligned with teeth and at other points teeth aligned with valleys no matter what you do
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Old 01-30-19, 09:25 PM
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Probably not a huge deal to go with a 42T, or even another 40T. Shifting might suffer in instrumented testing but maybe not in the real world.
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Old 01-30-19, 09:54 PM
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Are the rings you are looking at described as ramped and pinned? Which do work better in matched pairs.
Guessing your setup, with a five speed freewheel, dates back to before the introduction of such rings.
Your needs would probably be met by plain, non-ramped and pinned rings. Which are usually cheaper and compatible with a variety of ring sizes.
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Old 01-30-19, 11:02 PM
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?Un disclosed is the bolt circle diameter.. measure research that...

Ramped and pinned is meaningless on inner chainrings, particularly in the 5 by 2 era .. that was not a thing for many decades later..

( Maybe the OP has a riveted together one ... IDK.. no details offered )


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Old 01-30-19, 11:19 PM
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I would think that since you are planning to go to a larger inner ring and thus making the difference between the two only 10 teeth, you should not have a problem. This can sometimes be a problem when going to a significantly smaller inner ring thus greatly increasing the difference between the two rings.

Yes ramps and pins help the chain climb up to the larger ring but are found on the larger ring so you should have no trouble with not having them on the smaller ring.

Do do check the bolt circle diameter (bcd) for your crankset so you get the proper size.
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Old 01-31-19, 11:42 AM
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For what it's worth , I have a Nishiki International that I converted to triple front chainrings - 48-36-24 with a 14-28 tooth 6 speed freewheel and I find I ride most of the time on the 36 tooth ring. If you are going to swap out rings I would see if you could go to 48-36.

Unless you are racing I can't see where you would need anything more than 48 teeth and with a 14-28 tooth freewheel you could negotiate almost any terrain. By the way Amazon has a 5 speed 14-28 tooth hyperglide (or copy) freewheel with ramps for about $10 or so which would be a great upgrade if you don't already have the new type.
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Old 01-31-19, 12:07 PM
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With a 5 speed cluster and mostly staying on the inner ring, I wouldn't worry about getting a matched pair of ramped and pinned rings. You only need that with modern, indexed front derailleur shifting systems. Just get an inner ring of the appropriate BCD (likely 130mm, but do check), and be happy.
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Old 01-31-19, 07:32 PM
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The BCD is 130mm. There is a spider on the drive side crank, the inner and outer rings mount on either side and can be unscrewed and removed and easily replaced. The outer is not ramped or pinned, these are both just plain flat chainrings. The sheet material that the inner is made from appears to be about 3mm thick with my cm ruler and calibrated eyeball, the chain looks a little narrow between the plates, but the ring is also cut narrower up at the teeth, I will have to make sure I look for that. There are a number of 130 BCD 40T and 42T chainrings on ebay, maybe now is the time to look while I have some time to be sort of selective
I appreciate the comments
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