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7 speed chainrings compatibility

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7 speed chainrings compatibility

Old 11-29-23, 02:12 PM
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7 speed chainrings compatibility

My current crankset is a 7 speed FC-1055 130bcd 5 bolt. It has 53/42 SG chainrings. Running an 8 speed chain with a 7 speed cassette on the back. I just replaced the chain and cassette and thought I might as well replace chainrings while I’m at it so everything is all new. All the chainrings are 130bcd 5 bolt.

The new 42t chainring looks a bit different. It’s marked SG-A. Looks like it might be a from a 9 speed? The tooth profile is much wider at the tip of the tooth compared to the originals that I have. Also much wider at the bolt mount and has recessed bolt hole compared to the original which is just flat. Looks like the new one is a model Y16P42000. Google that model number and you'll see what I mean with the wide teeth. Unfortunately I'm not allowed to post links/photos yet.

The new 53t chainring is also a bit different. It’s marked SG-A as well so that matches. The tooth profile seems more closely matched to the existing ones that I have. The only difference is that is has 2 sets of shifting pins opposite each other which my existing one doesn’t have. Looks like it’s an 8 speed for what I can tell? Looks just like the 8 speed FC-1056 big chainring on VeloBase.

I understand the matching of SG-A/B so that’s why I have 53/42 A’s for new ones. Looks like the during the 7 speed days they didn’t differentiate between A/B because the existing ones are all just marked SG.

Questions:
  1. The 42t ring is way fatter at the mount hole than the existing one and hangs over the mount compared to the flush existing one. Is this an issue (it does seem to bolt through just fine)? The tooth profile seems much different too – much wider at the tip of the teeth. Was this a change from the 9 speed chainrings from the 7/8 ones?
  2. Can I use the new chainrings together with my new 7 speed cassette, current crank and 8 speed chain and not see any decrease in shifting performance? (everything worked just fine but that was on the old chain and cassette). I’m sure it will all work but I don’t want to see any performance decrease because of the mixing/matching.
  3. Am I overthinking all of this? lol
I have photos of all these to explain better but unfortunately I can't upload them yet because I'm new.
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Old 11-29-23, 05:14 PM
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If your front shifting is friction, any chainrings will work, and all of them will shift better than you do. The 130 mm bp;t circle of your 105 crankset limits you a 39 tooth small ring. (38s are available, but being from TA, they ain't cheap.) 53T big rings are, imho, kinda silly for normies, but that's a preference thing. On a 130, I'd probably go 50/39 or 48/39, depending on how the gear chart looked, but that's just me.

--Shannon
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Old 11-29-23, 05:27 PM
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Originally Posted by ShannonM
If your front shifting is friction, any chainrings will work, and all of them will shift better than you do. The 130 mm bp;t circle of your 105 crankset limits you a 39 tooth small ring. (38s are available, but being from TA, they ain't cheap.) 53T big rings are, imho, kinda silly for normies, but that's a preference thing. On a 130, I'd probably go 50/39 or 48/39, depending on how the gear chart looked, but that's just me.

--Shannon
Thanks for the response. I'm quite happy with the 53/42 and indexed 7 speed downtube 105sc . Not interested in friction or interested in a 50/39 or purchasing any additional chainrings other than what I currently have in my original post. More just curious if the questions/new chainrings I described above will work fine with what I have - (Indexed downtube 105sc shifter, new 7 speed cassette, new 8 speed chain, existing fc-1055 crankset). I assume if you're saying the front mech is setup as friction - I have no issues?

Last edited by bharris16; 11-29-23 at 05:47 PM.
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Old 11-29-23, 05:58 PM
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Originally Posted by bharris16
Thanks for the response. I'm quite happy with the 53/42 and indexed 7 speed downtube 105sc . Not interested in friction or interested in a 50/39 or purchasing any additional chainrings other than what I currently have in my original post. More just curious if the questions/new chainrings I described above will work fine with what I have - (Indexed downtube 105sc shifter, new 7 speed cassette, new 8 speed chain, existing fc-1055 crankset).
Short answer- Yes but.

Longer answer- As long as the ring bolts secure the rings well, and the ring/teeth center to center is supported by the rest of the system (if indexed), the thickness of the ring at that bolt has very little to do with general function. The one aspect that can be in play is if you ride in the small ring and the smaller rear cogs (crossover) in that with a thicker ring and/or shifting lift pins that slightly stick out the chain can rub or snag on the large ring's inner face.

To save cost many cranks on new bikes have come with steel rings which usually are thinner to save weight. Aftermarket rings are often not those "entry level" steel ones, Al rings are often made from thicker stock. Andy
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Old 11-29-23, 10:24 PM
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Originally Posted by ShannonM
If your front shifting is friction, any chainrings will work, and all of them will shift better than you do. The 130 mm bp;t circle of your 105 crankset limits you a 39 tooth small ring. (38s are available, but being from TA, they ain't cheap.) 53T big rings are, imho, kinda silly for normies, but that's a preference thing. On a 130, I'd probably go 50/39 or 48/39, depending on how the gear chart looked, but that's just me.

--Shannon
Using a 50 with a 12 in back just wears parts faster than if you used a 53 with a 13.
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Old 11-30-23, 12:28 AM
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Originally Posted by Kontact
Using a 50 with a 12 in back just wears parts faster than if you used a 53 with a 13.
You are correct, but, as with all things, it depends on what you want to optimize, and what you're willing to give up.

The highest gear on my road bike is a 45/14. It's a bit low for my taste, in the few situations where I use it, but it's never slowed me down when it mattered. A 13t or 12t small cog would be fine. I've never felt a real need for a gear over 100", even when I had them, and these days, I don't even want one, given the compromises that come with large big rings. (There are, of course, compromises with smaller big rings as well, but they make more sense for me and how I ride, so that's what I do.)

This is OT to the OP, so I'll stop now.

--Shannon
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