Go Back  Bike Forums > Bike Forums > Bicycle Mechanics
Reload this Page >

Need a lower gear

Notices
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.

Need a lower gear

Old 04-25-09, 02:53 PM
  #1  
Genius
Thread Starter
 
FlatMaster's Avatar
 
Join Date: Jan 2008
Location: Auburn, AL
Posts: 324

Bikes: Specilized Sirrus

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Need a lower gear

After attempting a steep grade in my new hilly home today, I realized I need lower gearing for a century comming up in two weeks. I also don't mind sactificing my topmost gear, so I think I might change both chanrigns.

Currently, I'm running Hyperglide 13...28 in the back. In the front, I have 42,52 Biopace. I'm tending towards choosing a smaller set of chainrings rather than a larger casette. First, I'd like to get of the Biopace. My questions...

So far, on combination that creates the lowest position for the chain at the FD, I have about 12 mm of clearence between the chain and the bottom of the FD. Any idea how small of a chainring I can get without needing to move the FD? The bike is older and I'd rather not need to move the FD.
FlatMaster is offline  
Old 04-25-09, 03:38 PM
  #2  
cycles per second
 
Gonzo Bob's Avatar
 
Join Date: Oct 2003
Location: Minnesota
Posts: 1,930

Bikes: Early 1980's Ishiwata 022 steel sport/touring, 1986 Vitus 979, 1988 DiamondBack Apex, 1997 Softride PowerWing 700, 2001 Trek OCLV 110

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 44 Post(s)
Liked 71 Times in 48 Posts
Biopace 52x42 is almost certainly a 130mm BCD crank. Biopace was also made for 110mm BCD but those were typically triples with 48x38x28 or 46x36x26.

The smallest round ring for a 130mm bolt circle is 38. I believe the smallest Biopace for 130mm is 40 but you may not be able to find one.

If you get a smaller large ring, you will probably want to lower the front derailer - about 2mm per tooth reduction (e.g. if you go from 52 to 50, lower the front derailer by about 4mm) - or you may have poor shifting.
Gonzo Bob is offline  
Old 04-25-09, 03:59 PM
  #3  
AEO
Senior Member
 
AEO's Avatar
 
Join Date: Jun 2007
Location: A Coffin Called Earth. or Toronto, ON
Posts: 12,258

Bikes: Bianchi, Miyata, Dahon, Rossin

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 3 Post(s)
Likes: 0
Liked 5 Times in 5 Posts
if you need a lower gear than 38x28, you will need a different crankset.
__________________
Food for thought: if you aren't dead by 2050, you and your entire family will be within a few years from starvation. Now that is a cruel gift to leave for your offspring. ;)
https://sanfrancisco.ibtimes.com/arti...ger-photos.htm
AEO is offline  
Old 04-26-09, 02:17 AM
  #4  
meb
Senior Member
 
meb's Avatar
 
Join Date: Aug 2003
Location: arlington, VA
Posts: 1,764
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 6 Post(s)
Likes: 0
Liked 5 Times in 4 Posts
Originally Posted by Gonzo Bob
Biopace 52x42 is almost certainly a 130mm BCD crank. Biopace was also made for 110mm BCD but those were typically triples with 48x38x28 or 46x36x26.

The smallest round ring for a 130mm bolt circle is 38. I believe the smallest Biopace for 130mm is 40 but you may not be able to find one.

If you get a smaller large ring, you will probably want to lower the front derailer - about 2mm per tooth reduction (e.g. if you go from 52 to 50, lower the front derailer by about 4mm) - or you may have poor shifting.
Since he has a Biopace 42, he probably can go to 38 round without lowering the FD-certainly wouldn't on the more easily located 39s.
meb 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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread

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

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.