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.

replacing chain ring

Old 03-18-08, 05:07 PM
  #1  
Plow13
Senior Member
Thread Starter
 
Plow13's Avatar
 
Join Date: Jan 2006
Location: Pittsburgh, PA
Posts: 1,212

Bikes: Lemond Alpe d'Huez 2005

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
replacing chain ring

i just got a single speed bianchi san jose. http://www.bianchiusa.com/08_san_jose.html

it has a 42t ring up front and a 17t cog in the back...i live in a very hilly area and i wanted to switch out the ring up front. Can i buy this ring and have it fit my new bike?
http://www.rei.com/product/698240

in other words what bcd do i have to get when i buy a chain ring?
Plow13 is offline  
Old 03-18-08, 05:12 PM
  #2  
barba
Senior Member
 
barba's Avatar
 
Join Date: Nov 2005
Posts: 4,083
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
You have to make sure the BCD of your crank is the same as the ring. I think the XD is 110mm and the ring you link is as well, but I would double check. It can be easier and more convenient to change the rear cog or freewheel. I keep several different sized cogs and freewheels around. They are fairly easy to swap around to get a different gear. Play with a gear calculator to compare different ratios.
barba is offline  
Old 03-18-08, 05:15 PM
  #3  
HillRider 
Senior Member
 
Join Date: Aug 2005
Location: Pittsburgh, PA
Posts: 31,342

Bikes: '''96 Litespeed Catalyst, '05 Litespeed Firenze, '06 Litespeed Tuscany, '12 Surly Pacer, All are 3x8,9 or 10. It is hilly around here!

Mentioned: 30 Post(s)
Tagged: 0 Thread(s)
Quoted: 1089 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
You can get a smaller chainring but the smallest you can go will be determined by the BCD (bolt circle diameter) of your crank. I'm not sure about the Suguino crank on your bike but if it has a BCD of 130 mm then 38T is the smallest that will fit. If it has a BCD of 110 mm you can fit a 34T ring.

BTW,It would be a lot cheaper to get a larger rear cog. A 19T cog would give the same gearing as reducing the 42T chainring to a 38T and a 21T cog would be the same as going to a 34T chainring.
HillRider is offline  
Old 03-18-08, 05:40 PM
  #4  
Plow13
Senior Member
Thread Starter
 
Plow13's Avatar
 
Join Date: Jan 2006
Location: Pittsburgh, PA
Posts: 1,212

Bikes: Lemond Alpe d'Huez 2005

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
if I get a bigger cog...do I have to replace the chain?
Plow13 is offline  
Old 03-18-08, 05:43 PM
  #5  
barba
Senior Member
 
barba's Avatar
 
Join Date: Nov 2005
Posts: 4,083
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
It depends on how much bigger and how much room you have in the track ends. For each tooth difference you will need about 3mm of movement of the axle in the track end.
barba is offline  
Old 03-18-08, 11:31 PM
  #6  
MrCjolsen
Senior Member
 
MrCjolsen's Avatar
 
Join Date: Nov 2004
Location: Davis CA
Posts: 3,957

Bikes: Surly Cross-Check, '85 Giant road bike (unrecogizable fixed-gear conversion

Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 3 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
OK, I've done this a zillion times.

I'm pretty sure the bcd on your crankset is 110mm. Thus the cranks you have work with the chainring you wish to purchase.

In my opinion, it's easier to swap out chainrings than cogs. No need for special tools, and no risk of damaging threads on the hub. An inexpensive chainring can be found for $20. The beauty of singlespeed is that you can use lots of cheap bmx parts.

If you are going from 42t rings to a 39t ring, I'm pretty sure you will need to shorten your chain.
MrCjolsen is offline  
Old 03-18-08, 11:42 PM
  #7  
Sixty Fiver
Bicycle Repair Man !!!
 
Sixty Fiver's Avatar
 
Join Date: Sep 2007
Location: YEG
Posts: 27,276

Bikes: See my sig...

Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 43 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
The beauty of running a bigger cog (and leaving the chain ring as is) is that it will also make the bike's drive smoother.

Having a few ss freewheels and the proper freewheel tool makes swapping things pretty easy as does having a few chain rings... neither is very hard to do and you might be able to run one chain with two freewheels if their differential isn't that great. 3 teeth seems to be the norm for maximum difference before the chain needs to be lengthened / shortened)

For a while I had a 42:14 on my Carlton which was good for everyday riding and also had a 52 tooth crank and spider that I could swap in if I was feeling like going insanely fast... that warranted another chain.

Now I just run a 52:18 on both my road bikes which is almost the same gearing as a 42:14 but is so much smoother.
Sixty Fiver is offline  
Old 03-19-08, 03:54 AM
  #8  
MrCjolsen
Senior Member
 
MrCjolsen's Avatar
 
Join Date: Nov 2004
Location: Davis CA
Posts: 3,957

Bikes: Surly Cross-Check, '85 Giant road bike (unrecogizable fixed-gear conversion

Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 3 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
You are right about the smoothness issue. I've recently been trending upward with regard to cog and ring sizes.
MrCjolsen is offline  
Old 03-19-08, 12:24 PM
  #9  
Owner
Senior Member
 
Join Date: Jun 2007
Posts: 230

Bikes: a green one and a black one

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Like others have said, it looks like you have a 110bcd crank. Here's a chart you can use to confirm the bcd by measuring between two adjacent bolts: http://sheldonbrown.com/gloss_bo-z.html#bcd

If your hills are long, then you might want to switch to a freewheel (with brakes) if you aren't running one already. If you're gearing down for the uphills, you'll spin out that much sooner on the descents. The first real climb I did on a fixed gear was about six miles, and the long descent was way harder then going up.
Owner is offline  

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


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.