Cycling and bicycle discussion forums. 
   Click here to join our community Log in to access your Control Panel  


Go Back   > >

Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

User Tag List

Reply
 
Thread Tools Search this Thread
Old 09-24-08, 11:08 AM   #1
MONGO!
Senior Member
Thread Starter
 
MONGO!'s Avatar
 
Join Date: Jun 2007
Location: Portland, OR
Bikes:
Posts: 4,279
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
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?
MONGO! is offline   Reply With Quote
Old 09-24-08, 12:55 PM   #2
TallRider
me have long head tube
 
TallRider's Avatar
 
Join Date: Oct 2005
Location: Chapel Hill, NC
Bikes:
Posts: 4,106
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
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.
TallRider is offline   Reply With Quote
Old 09-24-08, 12:59 PM   #3
MONGO!
Senior Member
Thread Starter
 
MONGO!'s Avatar
 
Join Date: Jun 2007
Location: Portland, OR
Bikes:
Posts: 4,279
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
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?
MONGO! is offline   Reply With Quote
Old 09-24-08, 01:09 PM   #4
TallRider
me have long head tube
 
TallRider's Avatar
 
Join Date: Oct 2005
Location: Chapel Hill, NC
Bikes:
Posts: 4,106
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
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.
TallRider is offline   Reply With Quote
Old 09-24-08, 01:50 PM   #5
MONGO!
Senior Member
Thread Starter
 
MONGO!'s Avatar
 
Join Date: Jun 2007
Location: Portland, OR
Bikes:
Posts: 4,279
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
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?
MONGO! is offline   Reply With Quote
Old 09-24-08, 02:09 PM   #6
TallRider
me have long head tube
 
TallRider's Avatar
 
Join Date: Oct 2005
Location: Chapel Hill, NC
Bikes:
Posts: 4,106
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
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%
TallRider is offline   Reply With Quote
Old 09-24-08, 02:20 PM   #7
MONGO!
Senior Member
Thread Starter
 
MONGO!'s Avatar
 
Join Date: Jun 2007
Location: Portland, OR
Bikes:
Posts: 4,279
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
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?
MONGO! is offline   Reply With Quote
Old 01-10-09, 09:47 PM   #8
bikeybikebike
Economists do it w/models
 
Join Date: Aug 2005
Location: Ottawa/Toronto
Bikes:
Posts: 591
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
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?
bikeybikebike is offline   Reply With Quote
Old 01-11-09, 03:01 AM   #9
meb
Senior Member
 
meb's Avatar
 
Join Date: Aug 2003
Location: arlington, VA
Bikes:
Posts: 1,745
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
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.
meb is offline   Reply With Quote
Old 01-11-09, 07:32 AM   #10
zacster
Senior Member
 
Join Date: Jul 2004
Location: Brooklyn NY
Bikes:
Posts: 4,966
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
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.
zacster is offline   Reply With Quote
Old 01-11-09, 10:16 AM   #11
joejack951
Senior Member
 
joejack951's Avatar
 
Join Date: May 2004
Location: Wilmington, DE
Bikes: 1984 Trek 660, 2003 Specialized Hardrock, 2004 LOOK KG386i, 2005 Iron Horse Warrior Expert, 2009 Pedal Force CX1, 2014 Islabikes CNOC 14 (son's)
Posts: 9,938
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 54 Post(s)
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.
joejack951 is offline   Reply With Quote
Old 01-13-09, 03:23 AM   #12
K6-III
Senior Member
 
Join Date: Jul 2003
Location: Brooklyn, NY
Bikes:
Posts: 1,453
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
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)
K6-III is offline   Reply With Quote
Old 01-13-09, 08:35 AM   #13
demoncyclist 
Senior Member
 
demoncyclist's Avatar
 
Join Date: Oct 2002
Location: Medway, MA
Bikes: 2011 Lynskey Sportive, 1988 Cannondale SM400
Posts: 2,685
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
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).
__________________
DEMON

Satanic Mechanic
STAR 3 Spinning Instructor

2011 Lynskey Sportive (Shimano Ultegra 10s)
1988 Cannondale SM400 (Suntour XC-M 7s)
demoncyclist is offline   Reply With Quote
Old 01-13-09, 08:41 AM   #14
cyccommute 
Mad bike riding scientist
 
cyccommute's Avatar
 
Join Date: Nov 2004
Location: Denver, CO
Bikes: Some silver ones, a black one, a red one, an orange one and a couple of titanium ones
Posts: 17,801
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 70 Post(s)
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.
__________________
Stuart Black
New! Pokin' around the Poconos A cold ride around Lake Erie
New! Dinosaurs in Colorado A mountain bike guide to the Purgatory Canyon dinosaur trackway
Solo Without Pie. The search for pie in the Midwest.
Picking the Scablands. Washington and Oregon, 2005. Pie and spiders on the Columbia River!
Days of Wineless Roads. Bed and Breakfasting along the KATY
Twisting Down the Alley. Misadventures in tornado alley.
An Good Ol' Fashion Appalachian Butt Whoopin'.
cyccommute is offline   Reply With Quote
Old 01-14-09, 02:08 AM   #15
meb
Senior Member
 
meb's Avatar
 
Join Date: Aug 2003
Location: arlington, VA
Bikes:
Posts: 1,745
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
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.
meb is offline   Reply With Quote
Old 01-14-09, 01:15 PM   #16
bikeybikebike
Economists do it w/models
 
Join Date: Aug 2005
Location: Ottawa/Toronto
Bikes:
Posts: 591
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
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?
bikeybikebike is offline   Reply With Quote
Old 01-14-09, 04:42 PM   #17
joejack951
Senior Member
 
joejack951's Avatar
 
Join Date: May 2004
Location: Wilmington, DE
Bikes: 1984 Trek 660, 2003 Specialized Hardrock, 2004 LOOK KG386i, 2005 Iron Horse Warrior Expert, 2009 Pedal Force CX1, 2014 Islabikes CNOC 14 (son's)
Posts: 9,938
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 54 Post(s)
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.
joejack951 is offline   Reply With Quote
Old 01-14-09, 06:14 PM   #18
DiabloScott
It's MY mountain
 
DiabloScott's Avatar
 
Join Date: Sep 2006
Location: Mt.Diablo
Bikes:
Posts: 6,697
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 67 Post(s)
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.
DiabloScott is offline   Reply With Quote
Old 01-15-09, 05:18 PM   #19
bikeybikebike
Economists do it w/models
 
Join Date: Aug 2005
Location: Ottawa/Toronto
Bikes:
Posts: 591
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
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?
bikeybikebike is offline   Reply With Quote
Old 01-15-09, 05:30 PM   #20
DiabloScott
It's MY mountain
 
DiabloScott's Avatar
 
Join Date: Sep 2006
Location: Mt.Diablo
Bikes:
Posts: 6,697
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 67 Post(s)
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 05:34 PM.
DiabloScott is offline   Reply With Quote
Old 01-15-09, 10:34 PM   #21
bikeybikebike
Economists do it w/models
 
Join Date: Aug 2005
Location: Ottawa/Toronto
Bikes:
Posts: 591
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
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
bikeybikebike is offline   Reply With Quote
Old 01-16-09, 08:22 PM   #22
acorn_user
Senior Member
 
Join Date: Dec 2005
Location: Charlottesville, Virginia
Bikes: Dawes Kalahari, Puch Prima Super Sport, Graham Weigh 853
Posts: 1,990
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
@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.
acorn_user is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -6. The time now is 12:37 PM.