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  1. #1
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    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!

  2. #2
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    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

  3. #3
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    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.

  4. #4
    cyclist/gearhead/cycli... moxfyre's Avatar
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    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!
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  5. #5
    cyclist/gearhead/cycli... moxfyre's Avatar
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    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!
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  6. #6
    Senior Member godspiral's Avatar
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    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.

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