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 09-20-06, 02:39 PM   #1
hackybiker
Senior Member
Thread Starter
 
Join Date: Aug 2006
Location: Philly
Bikes:
Posts: 110
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
upgrading a chainring for hills on old Fuji

Hi,

I recently got an old (1984-ish) Fuji road bike that I like a lot. Only problem is, I want to change the gearing to make it better for climbing very steep hills. I want to do it myself, since I like tinkering and learning about bike mechanics.

I've done as much research as I could on bikeforums and sheldonbrown.com, but I still have some questions. Here's what's on the bike:

6-gear cassette (13-26)
42, 52 chainrings (5-bolt, 110mm BCD)
Sugino RT crankset (170mm)

Questions:
1) I've seen a 39T chainring that I think might fit. Does anything smaller than 39T exist? Can anyone suggest an online store with a good selection of chainrings?
2) Is it a problem for the derailleur to have two chainrings of very different sizes (say, a 52T and a 30T, if the latter exists)?
3) Sheldon Brown says derailleurs are designed for the larger chainring, so that means I can't change out the 52T. Uh... right?
4) Would I need to do anything with the front derailleur? or the chain length (shorten or lengthen it)?

Thanks for any advice or pointers to additional info!
hackybiker is offline   Reply With Quote
Old 09-20-06, 03:24 PM   #2
Al1943
Senior Member
 
Join Date: Feb 2005
Location: Oklahoma
Bikes: Trek 5500, Colnago C-50
Posts: 9,433
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Yes, you can go quite a bit smaller than 39 on a 110 mm spider. For better shifting performance try to keep the big ring to inner ring differential at 14 or less. A 52/38 should work well, or a 50/36. Compact cranksets, 110 BCD, are often equipped with 50/34 chainirngs, but I think that's a stretch. A 48/34 would be a good combination if the front derailleur can be lowered enough. Individual chainrings are available on-line from Sheldon Brown or Peter White. Your LBS may also be a good source.

Al
Al1943 is offline   Reply With Quote
Old 09-20-06, 10:47 PM   #3
Phoible
Senior Member
 
Join Date: Jun 2006
Bikes:
Posts: 159
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
It is possible that an older derailleur could have trouble with a 14 or 16T difference. But in that case, you could just replace the front derailleur.
Phoible is offline   Reply With Quote
Old 09-20-06, 11:29 PM   #4
moxfyre
cyclist/gearhead/cycli...
 
moxfyre's Avatar
 
Join Date: Oct 2004
Location: DC / Maryland suburbs
Bikes: Homebuilt tourer/commuter, modified-beyond-recognition 1990 Trek 1100, reasonably stock 2002-ish Gary Fisher Hoo Koo E Koo
Posts: 4,166
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by hackybiker
Questions:
1) I've seen a 39T chainring that I think might fit. Does anything smaller than 39T exist? Can anyone suggest an online store with a good selection of chainrings?
2) Is it a problem for the derailleur to have two chainrings of very different sizes (say, a 52T and a 30T, if the latter exists)?
3) Sheldon Brown says derailleurs are designed for the larger chainring, so that means I can't change out the 52T. Uh... right?
4) Would I need to do anything with the front derailleur? or the chain length (shorten or lengthen it)?

Thanks for any advice or pointers to additional info!
Al1943's advice is spot on! You might be better off going to something like 50/36. Front derailers are designed for a specific size of large chainring, but it's almost always possible to make a front derailer work very well with SMALLER chainrings than it was originally designed for.

Indexed front derailers are also optimized for a specific gap between the chainrings, e.g. 53-39=14, or 48-38=10, but since your FD isn't indexed, no worries about that except not to exceed a gap of 14 as Al suggests.

You'll likely need to shorten the chain if you use smaller chainrings, yes. That can be done with an ordinary chain tool and is a good idea.

Another suggestion: if you replace the chainrings, replace the chain AND freewheel as well. (You call it a 6-speed cassette, but it's actually a freewheel on a 1984 bike.) This will have several advantages: you won't wear out the new chainrings as fast as you would with an old worn chain. Read Sheldon Brown's chain article to find out how chain and sprocket wear contribute to each other in a vicious cycle. The other advantage of replacing the freewheel is that you could switch to 7-speed in the back easily AND you would also get a freewheel with modern shift ramps which makes shifting the rear derailer a LOT smoother.

If you decide to do this, Nashbar sells a very nice 7-speed freewheel for $20, and a good 6/7 speed chain for about $8.

Hope that helps!
moxfyre is offline   Reply With Quote
Old 09-20-06, 11:31 PM   #5
moxfyre
cyclist/gearhead/cycli...
 
moxfyre's Avatar
 
Join Date: Oct 2004
Location: DC / Maryland suburbs
Bikes: Homebuilt tourer/commuter, modified-beyond-recognition 1990 Trek 1100, reasonably stock 2002-ish Gary Fisher Hoo Koo E Koo
Posts: 4,166
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by hackybiker
Questions:
1) I've seen a 39T chainring that I think might fit. Does anything smaller than 39T exist? Can anyone suggest an online store with a good selection of chainrings?
2) Is it a problem for the derailleur to have two chainrings of very different sizes (say, a 52T and a 30T, if the latter exists)?
3) Sheldon Brown says derailleurs are designed for the larger chainring, so that means I can't change out the 52T. Uh... right?
4) Would I need to do anything with the front derailleur? or the chain length (shorten or lengthen it)?

Thanks for any advice or pointers to additional info!
Al1943's advice is spot on! You might be better off going to something like 50/36. Front derailers are designed for a specific size of large chainring, but it's almost always possible to make a front derailer work very well with SMALLER chainrings than it was originally designed for.

Indexed front derailers are also optimized for a specific gap between the chainrings, e.g. 53-39=14, or 48-38=10, but since your FD isn't indexed, no worries about that except not to exceed a gap of 14 as Al suggests.

You'll likely need to shorten the chain if you use smaller chainrings, yes. That can be done with an ordinary chain tool and is a good idea.

Another suggestion: if you replace the chainrings, replace the chain AND freewheel as well. (You call it a 6-speed cassette, but it's actually a freewheel on a 1984 bike.) This will have several advantages: you won't wear out the new chainrings as fast as you would with an old worn chain. Read Sheldon Brown's chain article to find out how chain and sprocket wear contribute to each other in a vicious cycle. The other advantage of replacing the freewheel is that you would have a freewheel with modern shift ramps... they make shifting the rear derailer a LOT smoother in many cases!

If you decide to do this, Nashbar sells very nice 6 and 7-speed freewheels for $20, and good 6/7 speed chains for about $8. A 7-speed freewheel works as a drop-in replacement for a 6-speed freewheel, so you could add an additional gear for no extra hassle.

Hope that helps!
moxfyre is offline   Reply With Quote
Old 09-21-06, 07:38 AM   #6
godspiral
Senior Member
 
godspiral's Avatar
 
Join Date: Jun 2006
Bikes:
Posts: 876
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
The gearing you have is low enough to go about 5 mph at 40rpm. I guess at slow rpms its a bit harder to keep a line, so its more anxious in traffic, but I've found it easier to breathe and maintain posture around that rpm rate than spinning lower gears at the same speed. If you want to go 4mph, walking up is easier than any gearing.
godspiral 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 08:52 AM.