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Chainring rubbing chainstay
Hey folks,
New to the forum and I'm trying to build up my first SS so cut me some slack. I had an old mtn bike, 2006 Giant Iguana that I am converting to a SS. I purchased a 46t Origin8 P/P crankset and a 107mm Shimano UN55 bb. I went to put the bike together and the chainring is rubbing on the chainstay. I know I have the bb installed in the right direction and its not just touching, full contact. The bb I took off was a 113mm, did I go downsize to far in spindle length? I don't think going to a 44t or a 42t chainring is going to solve my problem. The largest chainring was a 42t originally. Any help is appreciated. |
Buy a track/fixed frame is my cynical response.
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Originally Posted by TIMBERS44
(Post 18813833)
Hey folks,
New to the forum and I'm trying to build up my first SS so cut me some slack. I had an old mtn bike, 2006 Giant Iguana that I am converting to a SS. I purchased a 46t Origin8 P/P crankset and a 107mm Shimano UN55 bb. I went to put the bike together and the chainring is rubbing on the chainstay. I know I have the bb installed in the right direction and its not just touching, full contact. The bb I took off was a 113mm, did I go downsize to far in spindle length? I don't think going to a 44t or a 42t chainring is going to solve my problem. The largest chainring was a 42t originally. Any help is appreciated. |
Looks like on Origin8's site that the crankset you have calls for a 110mm spindle.
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What I read from origin8,107mm was the correct length. I had also read on the forum there were some questions on the correct length because they were mislabeled at one point.
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Originally Posted by TIMBERS44
(Post 18813962)
What I read from origin8,107mm was the correct length. I had also read on the forum there were some questions on the correct length because they were mislabeled at one point.
2. Do NOT use a Shimano UN55 110mm BB. They are asymmetrical and the spindle is a good 3-4mms farther out on the non drive side than they are on the drive side which would make your problem worse, not better. All UN55s are off by varying amounts but the 110 is off the most. I know this because I needed an asymmetrical BB for an oddball frame/build. Someone once posted a chart listing every UN55 length and the amount by which it was off center, but I can't find it. |
Agree with [MENTION=362748]SquidPuppet[/MENTION]. Measure your front chainline from the center of the seat tube first and adjust chainring/freewheel ratio to eliminate rubbing. Orrr... Just dimple the chainstay! Iguanas are steel frames, no? Not a big deal to put a small dimple on a steel chainstay. I've done it a few times.
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Combination of BB spacers and/or chainring spacers just might do it.
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First i've heard of this! I hope you find that chart, i'm curious..
Originally Posted by SquidPuppet
(Post 18814028)
1. What is your front chainline measurement currently?
2. Do NOT use a Shimano UN55 110mm BB. They are asymmetrical and the spindle is a good 3-4mms farther out on the non drive side than they are on the drive side which would make your problem worse, not better. All UN55s are off by varying amounts but the 110 is off the most. I know this because I needed an asymmetrical BB for an oddball frame/build. Someone once posted a chart listing every UN55 length and the amount by which it was off center, but I can't find it. |
Originally Posted by Unkle Rico
(Post 18814531)
First i've heard of this! I hope you find that chart, i'm curious..
This is a common post on the subject.
Originally Posted by mrblue
(Post 17612433)
I was recently trying to install a crankset, on a single speed bike, that uses a square taper bottom bracket. I was using a Shimano UN-55 BB with 107mm spindle length. As it turned out that spindle length was a bit too short (chainline was off and crank arms were too close to chainstays). So, I decided to try a Shimano UN-55 with 110mm spindle length.
I haven't had a chance to actually install the 110mm BB, however something does look odd to me. I noticed the drive side spindle on the UN-55 is the same length for both the 110 and the 107, while only the non-drive side is longer on the 110. Correct me if I'm wrong but that is still going to leave me with the same issue I was having, only now the non-drive crank arm will be further out. Am I missing something here? |
Use a longer BB, use spacers, or get a smaller ring.
One of the three will be your answer. |
My FG conversion is an old MTB, too, so I ran into similar constraints. It was originally designed to have a 48-38-28 crankset, and 45T is about the biggest chainring I can use without scraping. If you have to use a 42T to make things work out, it won't be the end of the world.
BTW, here's the link to the Sheldon Brown blog post about UN54 bottom brackets: Shimano UN54 Cartridge Bottom Brackets Relative Chainline ? Harris Cyclery Blog I was bored one afternoon and did the rest of the math to figure out the NDS lengths and by how far some of them were asymmetrical (I figure a difference of 1mm or less is close enough to call symmetrical ;)): Code:
Bottom Bracket/Spec Actual NDS DS Symmetrical? |
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