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  1. #1
    Member lem0ndrider's Avatar
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    Individual Chain Rings

    I have a Sora Triple, 52/42/30 and was wondering if I can replace the 42 for a 34? Are the sizes standard?

    Thanks

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    Chain rings are sort of standard, but there are subtle variations.

    The first and critical dimension is the number of chainring bolts, and the diameter of the circle they lie on (BCD). Those dimensions determine whether they actually fit the crank. SORA cranks use 110 BCD chainrings so a 34t is possible.

    But there are other less critical dimensions which may affect performance, and are less standardized.

    These are (in no particular order)

    Tooth offset, ie. where the center of the teeth is with respect to the mounting face of the ring. Most teeth are centered, but some are offset toward the inner or outer face. A change in offset will change the effective spacing of the ring.

    Mounting hole diameter. This is standard for the inner and middle (inner of a double), but can (rarely) be different for some grannies.

    Intended position. Chainrings have shift gates, pins or ramps which will be positioned according to whether the ring is intended for the outer, middle or inner position (no ramps or pins).

    Shift gate phasing. This is subtle, but the cut teeth, pins and ramps, are positioned so the chain will make the shift when the teeth are aligned so they slide immediately between the rollers. When the rings are out of phase, the tips of the teeth hit the rollers on a shift, causing a bit of a skip before they settle on the new chainring.

    So you can fit a 34t, and the odds are that things like offset and such will be OK, but it's unlikely it'll phase perfectly unless you stay with the same brand, and even then there's no assurance. Experienced riders who don't shift under load don't have problems with non-phased rings, but they can cause dropped chains or a skip if shifted under load. Also, keep in mind that large chainring size differences make shifting worse.
    Last edited by FBinNY; 08-29-12 at 05:57 AM.
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    Member lem0ndrider's Avatar
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    Thanks for the information. Would it be prudent then, to change my 52/42 to a 50/34?. I don't use the 30 anymore and replacing the whole crank seems expensive.
    Last edited by lem0ndrider; 08-29-12 at 06:06 AM. Reason: wrong size

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    You can change the 42 for a 36 or a 34 if the BCD of the spider is the right one (110).

    IMO you can do it all with a 42 unless you cant climb the stairs or you are old with weak knees. I bet you have a 32 cog in that cassette too, we did not have those back in the day when the cranksets were 52/42

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    Quote Originally Posted by lem0ndrider View Post
    Thanks for the information. Would it be prudent then, to change my 52/42 to a 50/34?. I don't use the 30 anymore and replacing the whole crank seems expensive.
    I wouldn't buy a new ring for the outer just to drop two teeth. But if you rarely use the 52t with the outer few cassette sprockets, it might make sense to go smaller and bring the gear range more into line with how you ride.

    Before replacing either chainring make a note of the gear combinations you use and those you don't. Then use a gear chart to see which chainrings will give you the range you need with your cassette. I assume you did something similar to decide on the 34t. By assessing your needs you might find that you'll be happier with a 48 or 46t outer chainring.
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    Quote Originally Posted by ultraman6970 View Post
    IMO you can do it all with a 42 unless you cant climb the stairs or you are old with weak knees. I bet you have a 32 cog in that cassette too, we did not have those back in the day when the cranksets were 52/42
    I love these dismissive statements about how others should be able to use certain gears because "...back in the day..." You bring your 42T small ring to nearby Maryland or West Virginia and we'll see how well it works.

    To the OP: If your crank has a 110 mm bolt circle you can fit a 34T chainring. I did the same thing for my son when he didn't want to use a triple but wanted a lower gear than the 52/42 provided. His crank was an older SR with a 110 mm BCD so it worked. The early Sora triple cranks were 110/74 and if you have one of these, you can make the change.
    Last edited by HillRider; 08-29-12 at 06:48 AM.

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    Fred-ish rogerstg's Avatar
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    Quote Originally Posted by lem0ndrider View Post
    Thanks for the information. Would it be prudent then, to change my 52/42 to a 50/34?. I don't use the 30 anymore and replacing the whole crank seems expensive.
    If you don't use the 30, why change the middle ring? Just ignore the small ring.

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    Sincerely i dont see the issue, if you do well good then I live in that area and some stuff is pretty hilly but for a regular rider IMO to keep that 42 wont make any difference, I'm sure he is doing recreational riding too... lower gear makes life easier that's the logic but we did not have that 20 years ago and nobody complained, in a matter of fact the 42 was standard, even some shimano cranksets came with a 47, others with 45 too. Well is her problem after all, right? dont see why the bitterness ... is cheaper for him do not change anything right?

    Quote Originally Posted by HillRider View Post
    I love these dismissive statements about how others should be able to use certain gears because "...back in the day..." You bring your 42T small ring to nearby Maryland or West Virginia and we'll see how well it works.

    To the OP: If your crank has a 110 mm bolt circle you can fit a 34T chainring. I did the same thing for my son when he didn't want to use a triple but wanted a lower gear than the 52/42 provided. His crank was an older SR with a 110 mm BCD so it worked. The early Sora triple cranks were 110/74 and if you have one of these, you can make the change.

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    Senior Member zukahn1's Avatar
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    Will if the OP wants to change the middle ring I don't see a problem if they get one with the right BCD. I would probably however go with 38 or maybe 36. 52 to 34 is pretty big jump and slightly smaller jump would likely work better and give more practical gear spacing between all 3 rings.

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    Quote Originally Posted by FBinNY View Post
    Chain rings are sort of standard, but there are subtle variations.

    The first and critical dimension is the number of chainring bolts, and the diameter of the circle they lie on (BCD). Those dimensions determine whether they actually fit the crank. SORA cranks use 110 BCD chainrings so a 34t is possible.
    Are you sure about that? The Shimano site shows that the current SORA triple has 130/74 BCD with 52-39-30 chainrings. All of the Shimano triples with 52-42-30 chainrings that I'm familiar with are 130/74 BCD.

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    Quote Originally Posted by Al1943 View Post
    Are you sure about that? The Shimano site shows that the current SORA triple has 130/74 BCD with 52-39-30 chainrings. All of the Shimano triples with 52-42-30 chainrings that I'm familiar with are 130/74 BCD.
    No, I'm not sure, I ride Campagnolo Chorus on road, and my older stuff is either Campy or Sun Tour.

    My first instinct was that as a road set it would be a 130mm, and I was going to post that a 34t wasn't an option. But I didn't want to be wrong, so I went to the Shimano site, and the first Sora crankset that came up was this one a 110mm double road. Not being a Shimano spec expert I went with that, not having any idea that Shimano would make a 110bcd double and a 130bcd triple in the same model.

    If you're familiar with my posts, I shy away from detail specs, and usually suggest people either measure or look them up for themselves. This is a good example why.
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  12. #12
    Senior Member zukahn1's Avatar
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    Some good points I dind't really fully think if the OP's crank is a 130bcd 38 would be the lowest they can run.

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    Quote Originally Posted by lem0ndrider View Post
    Thanks for the information. Would it be prudent then, to change my 52/42 to a 50/34?.
    No. The 34 also requires a 110mm bolt circle diameter while most road triples are 130mm for the outer rings.


    I don't use the 30 anymore and replacing the whole crank seems expensive.
    That's most likely because you have a monstrous rear cassette with pie plate sized cogs spaced far apart. You need to consider both ends when contemplating gearing changes. Both spacing, when you'll need to change rings, and total range are all significant.

    Get a tighter cassette. 12-23 (or maybe 14-23, or maybe 13-26 - it's more ambiguous) would be my choice in 10 cogs, 13-23 or 12-21 in 9, and 13-21 in 8.

    Assuming 10 cogs you're better off with the triple unless you can spin a 39x21 or 23 up almost everything you'll encounter (depending on whether you want an 11 or 12 starting cog) and manage everything else. With 9 cogs you can have a 19 or 21.

    While you can get close to the same range using a compact double and road triple, with a tight cogset the former means you'll be shifting the front derailleur a lot (over ten times more often) more with five cog changes in back to get to the next gear. Having run 50-34 x 13-23 9 speed (because it had the same range as 50-40-30x13-21 8 speed and two rings are better than three) where I shifted from 50x21 to 34x15 (five cogs away) on the small ring slowing below 17 MPH on a false flat up and back to 50x19 from 34x14 after speeding up past 19 MPH (that happens _a lot_) I advise against it (with a triple you can ride your middle ring for most flattish solo efforts).
    Last edited by Drew Eckhardt; 08-30-12 at 02:30 PM.

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    Member lem0ndrider's Avatar
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    My rear cassette is an 8 speed 13-26 and I have to admit I am a bit confused on the different gear combos. I am not a technical rider by any means but having being off the bike for 3 years and training for a MS165 this Sept, I thought I would look into possible upgrades. You guys have been great and helped me not make any purchasing mistakes. I had read that most combos were 50/34 and thought that was the way to go.......shows you how ignorant I am . I do notice when I am climbing, I am in the 42/26 and struggling but when I get into the 30, I kinda spin too fast and I don't want to stress the chain by moving to the big gear on the cassette. Any suggestions?
    Last edited by lem0ndrider; 08-30-12 at 02:40 AM.

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    Senior Member zukahn1's Avatar
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    One thing is you could change your cassette to a 12-28/30 which would give you little more gearing range without changing a lot on your bike. Another would be to change your small inner granny gear to a 32 or 34 which would be pretty easy. The modern 50/34 you mention is usually run with 10-26/28 9 or 10speed cassette which gives about the same gear range as you currently have.

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    Quote Originally Posted by ultraman6970 View Post
    Sincerely i dont see the issue, if you do well good then I live in that area and some stuff is pretty hilly but for a regular rider IMO to keep that 42 wont make any difference, I'm sure he is doing recreational riding too... lower gear makes life easier that's the logic but we did not have that 20 years ago and nobody complained, in a matter of fact the 42 was standard, even some shimano cranksets came with a 47, others with 45 too. Well is her problem after all, right? dont see why the bitterness ... is cheaper for him do not change anything right?
    No bitterness intended, just pointing out that the fact nothing lower than a 42 used to be available on road cranks doesn't mean we should still live with that limitation. Back then nobody complained because they didn't know any better.

    As to the Sora cranks, the early versions (late 90's) were indeed 110 doubles or 110/74 triples but they are now 130 mm doubles or 130/74 triples so it depends on which one the OP has. If it came 52/42/30 i expect it's a 130/74 and the 34T middle chainring won't work.
    Last edited by HillRider; 08-30-12 at 09:09 AM.

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    Your 42/26 is a Ratio very close to the 30/19,
    so you double shift both derailleurs at once.
    downshift in front, up shift in back.
    Then as the hill gets steeper you have several lower ratios to go to, in back.

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    Quote Originally Posted by lem0ndrider View Post
    My rear cassette is an 8 speed 13-26 and I have to admit I am a bit confused on the different gear combos.
    13-14-15-17-19-21-23-26

    There's no 16 or 18 cog. Most road riders want a 16 because the jump from 17 to 15 is big and there are situations where the 15 is too hard and the 17 spins too fast. Some like an 18 cog too although some think it feels about the same as the 17 and 19 next to it.

    Pushing on the pedals too hard and pedaling slow can be be very fatiguing - _Training and Racing With a Power Meter_ has an anecdote about a rider who got dropped every time he spent five minutes pedaling below 70 RPM at an intensity he could otherwise handle for an hour. It's hard on your knees. If that happens switch to a bigger cog. When you run out of cogs switch to a smaller ring noting that's a very significant change - with 42 x 26 about the same gear as 30 x 19 (this is a simple ratio - 26 / 42 * 30 = 18.6 which is closest to 19) moving directly to the 30 ring without a cog change too is three gears easier which is a bit much. Because of that many people like to change the rear derailleur at the same time as the front - I'd move two cogs smaller at the same time to end up in 30x21.

    You can also pedal too fast for comfort. This is trainable and something you want to work on because it's good for endurance, speed, and can make for less shifting but there are still limits. Moving between rings is also a big jump, with 42 x 13 nearly identical to 52 x 16. The next gear there is 52 x 15.

    52 x 26 and 30 x 13 should be avoided (they may not be quiet).

    I do notice when I am climbing, I am in the 42/26 and struggling but when I get into the 30, I kinda spin too fast and I don't want to stress the chain by moving to the big gear on the cassette. Any suggestions?
    Shift to the 30 ring and 21 cog. You're not going to stress anything.

    If you don't need 30x26 you want a 13-23 which adds the 16 cog, and if you don't need 30x23 a 13-21 may be better (with the 18 cog too). If 42x26 was easy for you on the steepest hills you might run 53-39 (or 50-39) x 13-21 but it's not. Compacts are not a good idea unless you're a bike company (fewer SKUs means bigger profits) or have a lot of cogs. I rode 50-34 x 13-23 9 cogs (with the same range and spacing as 50-40-30 x 13-21 8 cogs plus the belief that two rings are better than three) and it was horrible - every time I dropped below 17 MPH I shifted five cogs from 50x21 to 34x15 and when I accelerated past 19 MPH it was five cogs back from 34x14 to 50x19 and instead of riding 40x17 or 40x16 in the middle of the cassette I spent a lot of time in 50x21 and 34x14 one cog in from the end which were noisier. 11 cogs in back would have restored the better shift pattern and chain line from the triple ( 46-36x12-13-14-15-16-17-18-19-21-23-25) although an 11 speed cassette and chain can cost more than some bikes. I switched back to a triple when I moved on to 10 cogs.
    Last edited by Drew Eckhardt; 08-30-12 at 04:32 PM.

  19. #19
    7-speed doomsday prepper ThermionicScott's Avatar
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    Quote Originally Posted by rogerstg View Post
    If you don't use the 30, why change the middle ring? Just ignore the small ring.
    This. Swapping the rings to make a 50/34 double would probably wreck the nice chainlines the OP is getting now.
    Quote Originally Posted by chandltp View Post
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    Quote Originally Posted by zukahn1 View Post
    One thing is you could change your cassette to a 12-28/30 which would give you little more gearing range without changing a lot on your bike. Another would be to change your small inner granny gear to a 32 or 34 which would be pretty easy. The modern 50/34 you mention is usually run with 10-26/28 9 or 10speed cassette which gives about the same gear range as you currently have.
    A 12-28 with only 8 cogs would be horrible for road riding. Probably 12-13-14-16-18-20-24-28. Yuck.

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    7-speed doomsday prepper ThermionicScott's Avatar
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    Quote Originally Posted by Drew Eckhardt View Post
    A 12-28 with only 8 cogs would be horrible for road riding. Probably 12-13-14-16-18-20-24-28. Yuck.
    I probably shouldn't mention the 7-speed 12-28 or the 5-speed 14-28 I have on my road bikes, huh?
    Quote Originally Posted by chandltp View Post
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    having commonly used gear ratios requiring a double shift is a PIA..

    So wide doubles, there needs to be a lot of overlap..

    Benefit of a 42t in the middle is it spans the more commonly used ratios,
    and its on the chainline center.

    the 52 when you spin out the 13/42, the 30/19 for the lower range..

    Not so much a parts swap, as using what you have, better.

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    Quote Originally Posted by ThermionicScott View Post
    I probably shouldn't mention the 7-speed 12-28 or the 5-speed 14-28 I have on my road bikes, huh?
    I was thrilled when I realized that by moving to a new fangled 8 cog setup and triple crank I could have both a straight block (13-19) for the plains east of Boulder, CO and low gear like 42x28 (30x21, same thing) for the mountains west without changing wheels or free wheels.
    Last edited by Drew Eckhardt; 08-30-12 at 02:20 PM.

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    Member lem0ndrider's Avatar
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    Quote Originally Posted by fietsbob View Post
    having commonly used gear ratios requiring a double shift is a PIA..

    So wide doubles, there needs to be a lot of overlap..

    Benefit of a 42t in the middle is it spans the more commonly used ratios,
    and its on the chainline center.

    the 52 when you spin out the 13/42, the 30/19 for the lower range..

    Not so much a parts swap, as using what you have, better.
    Thats a great point. I think I may keep what i have and change the back to a 10 speed and learn more efficiency pedaling.

    Thanks everyone

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