Chainline / BB guestion on converting a Classic Hybrid to 1X drop bar bike
04-01-21, 03:51 PM
#1
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Chainline / BB guestion on converting a Classic Hybrid to 1X drop bar bike
I am planning to convert my mid 90's 3x7 flat bar hybrid to a more current 1x10 drop bar "gravel" bike. The bike has all of the original parts except for the wheels which have been moderately upgraded from single wall to double wall and the rear wheel is equipped with a Shimano Alivio FH-T4000 hub. Here is a pic of the bike. This bike is very similar to the mid 90's Trek Multitrack 700 series bikes that some of you may be more familiar with.
Below is a list of the of the drivetrain related parts that I have or expect to have:
have:
Gevenalle GX Shifters/ Brake Levers
Microshift Advent X Rear Derailleur for 1×10 Speed
Microshift Advent X 11-48T 10-Speed Cassette With Alloy Spider
KMC X10 Chain
expect to have:
Shimano FC-1050, 105 Crankset
Wolf Tooth 130 BCD Gravel/ CX/ Road Chainring
Wolf Tooth Set of 5 Chainring Bolts+Nuts for 1x
I've read through Sheldon Brown's All About Bicycle Chainline and Park Tool Chainline Concepts. If I understand correctly, my current front and rear chainline is 47.5. I expect the 10 speed cassette to move my rear chainline in to approximately 44.85. The 105 crank calls for a chainline of 43.5 with a bottom bracket spindle length of 113. That puts the the big ring's (which is where I expect the new single chainring to be positioned) chainline at 46. I think that the spindle length of 113 keeps my chainline within a reasonable tolerance. Square tapper bottom brackets aren't the most expensive part out there but I'd rather not be completely wrong right out of the blocks. Does it sound like the 113 BB is where I should start or do I need a different spindle length?
I have a thread over in Bicycle Mechanics with some additional information on my initial thought process but it is not getting much response and I thought I might get some different eyes and more responses to this more specific question here. Thanks for taking the time to read my thread.
Below is a list of the of the drivetrain related parts that I have or expect to have:
have:
Gevenalle GX Shifters/ Brake Levers
Microshift Advent X Rear Derailleur for 1×10 Speed
Microshift Advent X 11-48T 10-Speed Cassette With Alloy Spider
KMC X10 Chain
expect to have:
Shimano FC-1050, 105 Crankset
Wolf Tooth 130 BCD Gravel/ CX/ Road Chainring
Wolf Tooth Set of 5 Chainring Bolts+Nuts for 1x
I've read through Sheldon Brown's All About Bicycle Chainline and Park Tool Chainline Concepts. If I understand correctly, my current front and rear chainline is 47.5. I expect the 10 speed cassette to move my rear chainline in to approximately 44.85. The 105 crank calls for a chainline of 43.5 with a bottom bracket spindle length of 113. That puts the the big ring's (which is where I expect the new single chainring to be positioned) chainline at 46. I think that the spindle length of 113 keeps my chainline within a reasonable tolerance. Square tapper bottom brackets aren't the most expensive part out there but I'd rather not be completely wrong right out of the blocks. Does it sound like the 113 BB is where I should start or do I need a different spindle length?
I have a thread over in Bicycle Mechanics with some additional information on my initial thought process but it is not getting much response and I thought I might get some different eyes and more responses to this more specific question here. Thanks for taking the time to read my thread.
04-01-21, 04:33 PM
#2
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Is the BB shell 68mm wide?
04-01-21, 06:25 PM
#3
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As precise as I _need_ to be about some stuff, chainline ain't one of the stuff. I've pretty much ignored chainline since the '80s, just try to get the inner chainring as close to the chainstay as possible, and that's all she wrote. 1x/2x/3x doesn't make much difference, it seems, as long as I avoided indexed Suntour gear, everything shifts just fine. Nowadays with 1x, especially with the combo of wide cassettes, modern flexible chains, clutch rders and narrow-wide rings, I just try to get the ring as far inboard as practical, and leave it to the gear spirits to work the rest out.
I realize that doesn't necessarily help with your question, concretely, but I may get around to that. Just saying my thinking/approach would be looking for the bb spindle that gets the chainring as far inboard as practical, i/o looking at chainline numbers. Hard to say what that spindle length is in your particular case, because it depends on the chainring size you're using, which you didn't mention, and what's happening with your drive-side chainstay. Dimpled? How deep? Where is the dimple? From the pic of your cool Fisher it looks like a std 68mm bb, and probs nice chainstay indents for the original triple crank, so if 113mm is the std spindle length the FC-1050, I'd start there.
When I 1x a double crank, I usually put the ring on the inner position and use a BBG Bashguard on the outer position. My 1x rings tend to be on the smaller side, 34-40t, so the inner position tends to work fine. If you're going with a larger ring, 46-48t+, you may need to use the outer position due to chainstay interference.
Most of my 1x builds are using newer cranks/bbs, which don't have the range of spindle lengths we had with square tapers. But I'll be working on 1x-ing a vintage Harry Quinn over the next couple/few days, which will likely involve some spindle swapping tomfoolery.
The Schwinn Paramount in the 2nd photo below just got an upgrade to a Dura-Ace 7800 crank, 38t outer w/BBG. No pix yet.
I realize that doesn't necessarily help with your question, concretely, but I may get around to that. Just saying my thinking/approach would be looking for the bb spindle that gets the chainring as far inboard as practical, i/o looking at chainline numbers. Hard to say what that spindle length is in your particular case, because it depends on the chainring size you're using, which you didn't mention, and what's happening with your drive-side chainstay. Dimpled? How deep? Where is the dimple? From the pic of your cool Fisher it looks like a std 68mm bb, and probs nice chainstay indents for the original triple crank, so if 113mm is the std spindle length the FC-1050, I'd start there.
When I 1x a double crank, I usually put the ring on the inner position and use a BBG Bashguard on the outer position. My 1x rings tend to be on the smaller side, 34-40t, so the inner position tends to work fine. If you're going with a larger ring, 46-48t+, you may need to use the outer position due to chainstay interference.
Most of my 1x builds are using newer cranks/bbs, which don't have the range of spindle lengths we had with square tapers. But I'll be working on 1x-ing a vintage Harry Quinn over the next couple/few days, which will likely involve some spindle swapping tomfoolery.
The Schwinn Paramount in the 2nd photo below just got an upgrade to a Dura-Ace 7800 crank, 38t outer w/BBG. No pix yet.
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04-01-21, 10:07 PM
#4
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04-01-21, 10:12 PM
#5
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Thread Starter
I expect to use a 42 tooth chainring. I don't detect a dimple on the the chainstay; just a slight narrowing of the stay on the inside for tire clearance.
Last edited by JDandy; 04-02-21 at 08:42 AM.
04-03-21, 12:45 PM
#6
Newbie
Thread Starter
As precise as I _need_ to be about some stuff, chainline ain't one of the stuff. I've pretty much ignored chainline since the '80s, just try to get the inner chainring as close to the chainstay as possible, and that's all she wrote. 1x/2x/3x doesn't make much difference, it seems, as long as I avoided indexed Suntour gear, everything shifts just fine. Nowadays with 1x, especially with the combo of wide cassettes, modern flexible chains, clutch rders and narrow-wide rings, I just try to get the ring as far inboard as practical, and leave it to the gear spirits to work the rest out.
I realize that doesn't necessarily help with your question, concretely, but I may get around to that. Just saying my thinking/approach would be looking for the bb spindle that gets the chainring as far inboard as practical, i/o looking at chainline numbers. Hard to say what that spindle length is in your particular case, because it depends on the chainring size you're using, which you didn't mention, and what's happening with your drive-side chainstay. Dimpled? How deep? Where is the dimple? From the pic of your cool Fisher it looks like a std 68mm bb, and probs nice chainstay indents for the original triple crank, so if 113mm is the std spindle length the FC-1050, I'd start there.
When I 1x a double crank, I usually put the ring on the inner position and use a BBG Bashguard on the outer position. My 1x rings tend to be on the smaller side, 34-40t, so the inner position tends to work fine. If you're going with a larger ring, 46-48t+, you may need to use the outer position due to chainstay interference.
Most of my 1x builds are using newer cranks/bbs, which don't have the range of spindle lengths we had with square tapers. But I'll be working on 1x-ing a vintage Harry Quinn over the next couple/few days, which will likely involve some spindle swapping tomfoolery.
The Schwinn Paramount in the 2nd photo below just got an upgrade to a Dura-Ace 7800 crank, 38t outer w/BBG. No pix yet.
I realize that doesn't necessarily help with your question, concretely, but I may get around to that. Just saying my thinking/approach would be looking for the bb spindle that gets the chainring as far inboard as practical, i/o looking at chainline numbers. Hard to say what that spindle length is in your particular case, because it depends on the chainring size you're using, which you didn't mention, and what's happening with your drive-side chainstay. Dimpled? How deep? Where is the dimple? From the pic of your cool Fisher it looks like a std 68mm bb, and probs nice chainstay indents for the original triple crank, so if 113mm is the std spindle length the FC-1050, I'd start there.
When I 1x a double crank, I usually put the ring on the inner position and use a BBG Bashguard on the outer position. My 1x rings tend to be on the smaller side, 34-40t, so the inner position tends to work fine. If you're going with a larger ring, 46-48t+, you may need to use the outer position due to chainstay interference.
Most of my 1x builds are using newer cranks/bbs, which don't have the range of spindle lengths we had with square tapers. But I'll be working on 1x-ing a vintage Harry Quinn over the next couple/few days, which will likely involve some spindle swapping tomfoolery.
The Schwinn Paramount in the 2nd photo below just got an upgrade to a Dura-Ace 7800 crank, 38t outer w/BBG. No pix yet.
I have to assume that everyone that has read this thread agrees with your advice pcb.
It seems like a 113mm spindle length is where I should start. I may have a choice of placing the chainring outside or inside. The other spindle length option might be 110mm but that may be too far inward to allow the chainring to clear chainstay and likely no outside/inside option. So 113mm it is. Thanks.
