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  1. #1
    Senior Member MONGO!'s Avatar
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    Where can I get a smaller 130 BCD chainring?

    My wife's cross bike has 8 speed Sora with a 53/39 crank.

    Can I swap out the chainrings for smaller ones to make it more hill friendly?
    I'm having trouble finding smaller 130 BCD chainrings.

    Should I just swap the whole crankset?

  2. #2
    me have long head tube TallRider's Avatar
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    130mm BCD is limited in how small chainrings can be. It used to be the standard was 52/42 chainrings on a 130mm BCD double crank, nowadays it's 53/39. The smallest chainring you can get for 130mm BCD is 38t.

    If you really want to make the bike more hill-friendly, here are your options, not in any particular rank:

    1. replace the 130mm BCD double crank with a "compact double" 110mm BCD - typically 50/36 or 50/34 or 58/34 - you can keep your shifter and front derailer and everything else - you'll probably just need to lower the front derailer a little bit

    2. replace the cassette on the rear wheel with one that has more teeth - for example, if you have a 12-25, replace it with a 13-28 (if you can find that in 8-speed). This is your cheapest option, depending on what gears are already on the rear wheel and what you're able to find in replacement. Shimano road rear derailers are typically rated to a max cog of 27t but nearly always are fine with 28t and sometimes with 30t large cogs.

    3. get a triple crank. Sora brifters will work with a triple, but you'll also need to replace the front and rear derailers with ones that have capacity for a wider range of gears.

  3. #3
    Senior Member MONGO!'s Avatar
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    Quote Originally Posted by timcupery View Post
    130mm BCD is limited in how small chainrings can be. It used to be the standard was 52/42 chainrings on a 130mm BCD double crank, nowadays it's 53/39. The smallest chainring you can get for 130mm BCD is 38t.

    If you really want to make the bike more hill-friendly, here are your options, not in any particular rank:

    1. replace the 130mm BCD double crank with a "compact double" 110mm BCD - typically 50/36 or 50/34 or 58/34 - you can keep your shifter and front derailer and everything else - you'll probably just need to lower the front derailer a little bit

    2. replace the cassette on the rear wheel with one that has more teeth - for example, if you have a 12-25, replace it with a 13-28 (if you can find that in 8-speed). This is your cheapest option, depending on what gears are already on the rear wheel and what you're able to find in replacement. Shimano road rear derailers are typically rated to a max cog of 27t but nearly always are fine with 28t and sometimes with 30t large cogs.

    3. get a triple crank. Sora brifters will work with a triple, but you'll also need to replace the front and rear derailers with ones that have capacity for a wider range of gears.
    Thanks for the info.

    Will a compact double work with 8 speed?

  4. #4
    me have long head tube TallRider's Avatar
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    I think Compact double is probably your best option. It will work fine with 8-speed. Find a compact double that was designed for a 9-speed drivetrain if you can, but chainrings designed for 10-speed should still be okay. I'm not sure about that though, as I've not kept up on bike stuff in the past couple of years. Definitely 9-speed designed stuff will work with 8-speed chain, because 8- and 9-speed chains have the same inside width and thus work wtih the same width chainring teeth - I think the inside width of a 10-speed chain is narrower.
    I'm running 10-speed chainrings on a bike with 9-speed chain and rear gearing, though, and it works totally fine.

  5. #5
    Senior Member MONGO!'s Avatar
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    So, I'm thinking a Tiagra compact double will do the trick.

    Am I going to need a new BB too or can I use the one on the bike already?

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    me have long head tube TallRider's Avatar
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    You'll very likely need a new BB. In fact, I'm pretty sure the Tiagra compact double is an integrated crank/BB design. Even if you succeed in finding a square-taper 110mm double crank, it's likely that it will ideally be used with a different width bottom bracket than the Sora double - square-taper cranks weren't standardized as to what bottom bracket spindle lengths they would use to achieve proper chainline.
    You can go to eBay and look at Cranks in the road bike section and look for 50/34 or 50/36 or 48/34.
    Alternately, Nashbar has a compact double (50/34) for $60 and you'd need to buy an ISIS bottom bracket for around $25 to go with it. Likely your cheapest option.
    The Tiagra 50/34 crank is $90 but you'd need to buy the BB cups separately, probably another $30.

    If you could replace the cassette (option #2 that I listed) it would definitely be your cheapest option for getting lower gears.

    How much lower of gears?
    going from 39t to 34t small chainring is 87%.
    going from 23t to 28t large cog is 82%
    going from 25t to 28t large cog (Sora 8-speed is probably 12-25t cassette) is 89%

  7. #7
    Senior Member MONGO!'s Avatar
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    Quote Originally Posted by timcupery View Post

    If you could replace the cassette (option #2 that I listed) it would definitely be your cheapest option for getting lower gears.

    How much lower of gears?
    going from 39t to 34t small chainring is 87%.
    going from 23t to 28t large cog is 82%
    going from 25t to 28t large cog (Sora 8-speed is probably 12-25t cassette) is 89%

    Thanks for the help.

    There is a Tiagra crank w/BB for $95 BIN I may get.

    The cassette is a 13-26, I could put a 28 on there, probably not a 30 since it's a short cage RD.

    According to Sheldon's gear calculator changing to a compact crank will give a lowest gear inches of 34.4, keeping the crank and putting a 28 on the back would give 26.6, compared to the 39.4 it has now.

    I've never installed a BB (or crank for that matter) how tough a job is it?

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    Thought I would revive this thread, as I have a similar issue. Are there any options for crank and chainring replacements that will go with the bottom bracket that comes with the shimano sora?

    A triple may be desirable, but the current rings are doubles. How would i know if there is enough clearance?

  9. #9
    meb
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    Quote Originally Posted by bikeybikebike View Post
    Thought I would revive this thread, as I have a similar issue. Are there any options for crank and chainring replacements that will go with the bottom bracket that comes with the shimano sora?

    A triple may be desirable, but the current rings are doubles. How would i know if there is enough clearance?
    You might find someone with a similar frame that knows whether there is enough clearance-but the best prospect is to try.

    Keeping the same bottom bracket would give chainline problems even if you find you have clearance after installation. Whether those chainline issues are tolerable or substantial is to be determined.
    I'd plan on changing the bottom bracket if you went to a triple.

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    My understanding is that Japanese (JIS) square taper is different from the ISO/British/Italian standard, at least in the old days. Since most stuff is Japanese or Asian in origin now anyway, maybe you can find something that'll work. I have no specific recommendations. I was looking into this for Campy/Zeus compatibility questions so my 'expertise' is more on the other side of the world.

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    I want to make a general comment that I would not attempt to use a 9/10 speed crank with an 8 speed system unless you plan on using a 9/10 speed chain. The ramps on the 9/10 rings are significantly larger than 8 speed ramps and will allow very little deviation from a perfect chainline before the chain starts inadvertently getting caught on the ramps. The ramps will attempt to pick up the chain (as they are designed to do) when you really don't want them to. BTDT, and I don't recommend it.

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    It looks like Sugino makes a compact crank in square taper. www.chucksbikes.com is clearing out 160's for $30 (good if your wife is really short)
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  13. #13
    Senior Member demoncyclist's Avatar
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    But you will probably still need to swap the BB for one with a longer spindle, since the granny ring will cause clearance problems unless this is a longer wheelbase frame (the chainstay angles aren't as severe with longer stays).
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  14. #14
    Mad bike riding scientist cyccommute's Avatar
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    Quote Originally Posted by meb View Post
    You might find someone with a similar frame that knows whether there is enough clearance-but the best prospect is to try.

    Keeping the same bottom bracket would give chainline problems even if you find you have clearance after installation. Whether those chainline issues are tolerable or substantial is to be determined.
    I'd plan on changing the bottom bracket if you went to a triple.
    There would only be chainline issues if Mongo went with a triple. A compact crank would use the same chainline as the current crank. If the new crank has external bearings, the bottom bracket would have to be changed of course.
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    meb
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    Quote Originally Posted by cyccommute View Post
    There would only be chainline issues if Mongo went with a triple. A compact crank would use the same chainline as the current crank. If the new crank has external bearings, the bottom bracket would have to be changed of course.
    This branch of the thread is responsive to bikeybikebike's current question on triples, not Mongos original question of 4 months ago-the quote listed and the post root came from Bikeybikebike who explicitly asked a question on triples.

  16. #16
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    Quote Originally Posted by K6-III View Post
    It looks like Sugino makes a compact crank in square taper. www.chucksbikes.com is clearing out 160's for $30 (good if your wife is really short)
    Thanks for the help all, I am going to try desperately to avoid having to swap the BB. This is a budget/first bike, so i'm trying to make it as rideable as possible, for as little as possible.

    Will this fit the shimano BB, and will the Sora FD work on a compact?

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    Quote Originally Posted by bikeybikebike View Post
    Thanks for the help all, I am going to try desperately to avoid having to swap the BB. This is a budget/first bike, so i'm trying to make it as rideable as possible, for as little as possible.

    Will this fit the shimano BB, and will the Sora FD work on a compact?
    Your Sora BB should be a 110mm width according to Sheldon Brown's page. I cannot find any info on that particular Sugino crank though. Assuming Sugino uses the same spider design for their compact double as they do their touring triple, it has a chance of working. Sheldon claims that the correct BB length for the touring triples is 113-118mm but has a comment that 107mm works on some road bikes.

    I know that the triple Sora FD will shift to a 50 tooth ring without issue so I imagine that the double version will work just as well. The only issue would be if you had a braze-on FD and could not lower the derailler far enough in the bracket to get the right clearance. You could always grind away some of the bracket to make more room though in a pinch.

  18. #18
    It's MY mountain DiabloScott's Avatar
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    Compact cranks are nice.

    It'd be a lot cheaper and easier to put on a MTB derailleur and a 34t 8-speed cassette. You'd also have a lower low at the expense of slightly larger jumps between gears.
    http://diabloscott.blogspot.com/

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    Quote Originally Posted by joejack951 View Post
    Your Sora BB should be a 110mm width according to Sheldon Brown's page. I cannot find any info on that particular Sugino crank though. Assuming Sugino uses the same spider design for their compact double as they do their touring triple, it has a chance of working. Sheldon claims that the correct BB length for the touring triples is 113-118mm but has a comment that 107mm works on some road bikes.

    I know that the triple Sora FD will shift to a 50 tooth ring without issue so I imagine that the double version will work just as well. The only issue would be if you had a braze-on FD and could not lower the derailler far enough in the bracket to get the right clearance. You could always grind away some of the bracket to make more room though in a pinch.
    Thanks a bunch, I think the FD hanger is adjustable downwards so I should be alright. The current crankset is a double, and it doesn't look like it has ever been a triple so i'm hoping the swap will be an easy one.

    Quote Originally Posted by DiabloScott View Post
    Compact cranks are nice.

    It'd be a lot cheaper and easier to put on a MTB derailleur and a 34t 8-speed cassette. You'd also have a lower low at the expense of slightly larger jumps between gears.
    That's an interesting proposition, but i'm looking to replace the whole drivetrain as the chain, cassette, and chainrings are all pretty worn down. i've already purchased a new 12-25 cassette so i just need to replace the chainrings, and i'm not 100% sure how the sora indexing would work with the MTB derailleur.

    Any confirmed combinations?

  20. #20
    It's MY mountain DiabloScott's Avatar
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    Quote Originally Posted by bikeybikebike View Post
    That's an interesting proposition, but i'm looking to replace the whole drivetrain as the chain, cassette, and chainrings are all pretty worn down. i've already purchased a new 12-25 cassette so i just need to replace the chainrings, and i'm not 100% sure how the sora indexing would work with the MTB derailleur.

    Any confirmed combinations?
    But you can't replace the chainrings with anything smaller than you've already got so you're looking at a new crank and BB for at least $200 plus front derailleur repositioning, or a new cassette/derailleur combo for less than half that plus a new cable and a much easier installation.

    Sora 8-speed indexing is the same as every other Shimano 8-speed indexing road or MTB (one exception that doesn't matter to you). You already bought a new cassette - too bad.

    Putting a MTB derailleur and a wide cassette on a road bike is common and smart for people in your situation.
    Last edited by DiabloScott; 01-15-09 at 04:34 PM.
    http://diabloscott.blogspot.com/

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    Quote Originally Posted by DiabloScott View Post
    But you can't replace the chainrings with anything smaller than you've already got so you're looking at a new crank and BB for at least $200 plus front derailleur repositioning, or a new cassette/derailleur combo for less than half that plus a new cable and a much easier installation.

    Sora 8-speed indexing is the same as every other Shimano 8-speed indexing road or MTB (one exception that doesn't matter to you). You already bought a new cassette - too bad.

    Putting a MTB derailleur and a wide cassette on a road bike is common and smart for people in your situation.
    Well I was able to find a closeout sora cassette and a JIS crank/chainring combo for about $50 all said and done. I don't expect to have a problem repositioning the FD. Time and patience has allowed me to avoid paying 'regular' prices

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    @bikey bikey
    What shifters do you? Some Shimano shifters are EITHER double OR TRIPLE compatible. If you have double compatible shifters, you would have to replace them to run a triple, in which case a compact double (e.g. Sugino XD) would be preferable.

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