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Frog Whisperer
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Discussion Starter · #1 ·
So to calculate my “chain line” for the rear, If I have a 120mm spacing then the distance from the inside of the dropout on the chain side less ½ the thickness of the cog subtracted from ½ the total distance (60 in this case should be the chainline?…am I right? So 16mm from dropout to cog, ½ the thickness of the cog (3.8mm)…… 1.9 mm equals 42.1 Rounding to 42mm


Front chainline….32mm tube divided by 2= 16, 33.3 mm from outside of ring to tube… and ring measures 3.7mm (divided by 2 = 1.85) So 16 + 33.3= 49- 1.85 = 47.15 rounding to 47


Is my chainline really off by 5 mm? Or am I doing this all wrong? Sighting down the chain it sure looks good.. I put a 1 mm spacer in the rear today (between the cog and the hub). The cog has one side that has kinda a rim on it while the other side is flat. I have the flat against the hub is that right? I where to flip it around, and put the ring on the inside of the “spider” rather than on the outside it would be about perfect if my math is right. Can I do that? I believe I have the room to move the ring in (clearing the chain stay)

Am I making any sense?

It seems that on a stock bike (2005 Specialized Langster) it would be right from the factory.


Thanks and correct me if I am wrong, trust me won’t be the first time (today even).

This all started when I was reading about the drivetrain is supposed to be silent on a fixed.
 

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soy un perdedor
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The outer ring on a normal road double is 46mm. Track setups are 42mm. Normal track hub and cog combinations will give a chainline of 43ish mm. Maybe you have a normal double crank and BB?

Sheldon Brown is a great resource for this stuff. Look under "chainline" in his glossary.
http://www.sheldonbrown.com/gloss_ca-m.html

A good way to check chainline is to hang the bike up vertically by the front wheel and drop a string with a weight at the end from the chainring. Use a level along the length of the toptube to make sure the bike is perfectly vertical. Compare your cog position to the string position.
 

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Done with winter.
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I haven't seen a stock Langster in a while but I'm betting it's just a road crank and if they didn't correct for the chainline just move the chainring to the inner side of the spider. That will put you much closer to the rear chainline.
 

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I'm not familar with the crank on the Langster. Do you have a track crank? If so the ring should be on the outside(actually, the ring will only go on one side. there shouldn't be a lip on the inside of spider)..

If you are using a double crank, your ring should be on the inside. That will give you a 42mm chainline..

If the chainline looks good, I'd leave it and check the math again. If you have 36" ruler, it makes a good chainline checker. Lay the ruler flat against the outside of the cog. It should line up with outside of the ring
 

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Frog Whisperer
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Discussion Starter · #5 · (Edited)
I am going to move the ring to the inside tomorrow and see if there is a difference. It must be a regular double crank because there is def. a lip on the inside.. According Sheldon Brown's site, It seems like I am doing the math right.
 

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I have the flat against the hub is that right
Unfortunately, no. The flange, (or "rim") on the cog needs to point to the center of the hub. The lockring goes against the flat side of the cog.
 

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Martini time?
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I have an 06 LAngster.

I put a 42 chainring on my stock crank, stupid me didn't pay attention when pulling the 48 off. Put the new 42 on the outside, had a noisy drivetrain, dropped chain, and weird drag issues. Sighted down the chainline one day and wondered if inside would be better...swapped it over to the inside and Much Quieter!! No other complaints since then. Give it a try.
 

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Frog Whisperer
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Discussion Starter · #8 ·
well mine for sure came on the outside and in 45 minutes it will be on the inside...that will move it in close to 4 mm, with the 1 mm spacer on the rear it should be LOTS closer, I will get a 2 mm to replace the 1 if nec. I'd rather use a single than stack them, not sure why but I would. WIM, thanks a bunch that was an important issue and that IS how I installed it. 5mm sure doesn't look like much but I guess like my work.....a miss is a miss!

I have been trying to impress on my kids for years now, unlike grades in school, either something is right or it is wrong....a 96% may be an A but it is still 4% off! Any one out there in the real world get a 4% margin of error at work?
 

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Well, now I am confused. When speaking of the cog in your original post, you said you had its flat side against the hub, which is not where it needs to be. If the cog's flange is pointing away from the frame, you need to turn the cog around so the flange butts up against the hub. That would move the cog about 7 mm to the outside.

If the cog's flange is now butting up against the hub, ignore this post :D
 

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wim said:
Well, now I am confused. When speaking of the cog in your original post, you said you had its flat side against the hub, which is not where it needs to be. If the cog's flange is pointing away from the frame, you need to turn the cog around so the flange butts up against the hub. That would move the cog about 7 mm to the outside.

If the cog's flange is now butting up against the hub, ignore this post :D
Yep...This is how the cog should be screwed on the hub. The flange is on the inside facing the hub.
 

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Touch0Gray said:
I have been trying to impress on my kids for years now, unlike grades in school, either something is right or it is wrong....a 96% may be an A but it is still 4% off! Any one out there in the real world get a 4% margin of error at work?
That's silly and unrealistic. Hell, it would be great if Microsoft's margin of error was only 4%!
 

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Frog Whisperer
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Discussion Starter · #12 · (Edited)
how does this look?

I am sorry, you were rightly confused beacause I posted the original incorrectly, and I apologize.

I flopped the ring to the inside and ...voila, near perfect chainline, I may still pull the 1 mm shim out yet, sighting down from the top, using the top tube as a reference line, the rear may be out a bit far, but for now...HUGELY improved.

Now....the sounds I am hearing are from the 3 dollar chain they installed from the factory...gee go figure. I guess there is a difference between quiet and QUIET, When you gentlemen say quiet drive train, are we talking no tapping of the chain contacting the ring or cogs?.....

can any one say anal retentive?......... someone tell me to just stop it and turn the music up!

I better get back to work where I get paid for being that critical!

btw ISO 200, f:40, 9 seconds
 

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Frog Whisperer
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Discussion Starter · #13 ·
FTM said:
That's silly and unrealistic. Hell, it would be great if Microsoft's margin of error was only 4%!

well as silly and unrealistic as it may be, if I was to be 94% accurate in my shop I would have been out of business a LONG time ago. My customers expect perfection and always have. As is is I am going on 26+ years.

I would hesitate to compare myself to microsoft.....I am NOT one of the only 3 or 4 games in town!

Especially today, I just spent 2 hour REPAIRING what someone else had fixed.....there is a big difference....very big
 

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Touch0Gray said:
well as silly and unrealistic as it may be, if I was to be 94% accurate in my shop I would have been out of business a LONG time ago. My customers expect perfection and always have. As is is I am going on 26+ years.

I would hesitate to compare myself to microsoft.....I am NOT one of the only 3 or 4 games in town!
Not every mistake makes the final product just like not every mistake brings down an airplane or kills a patient. I'm sure you make errors throughout the day just not in the final delivery. Seriously, how many jobs are there in which there is only a right or a wrong without and fluctuation or variance? Assembly line work?

I come from a family of scientists and mathematicians where creative risk taking is encouraged and failure is expected. It tends to make for a more enjoyable life and a more interesting and lucrative career.
 

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Frog Whisperer
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Discussion Starter · #15 ·
FTM said:
Not every mistake makes the final product just like not every mistake brings down an airplane or kills a patient. I'm sure you make errors throughout the day just not in the final delivery. Seriously, how many jobs are there in which there is only a right or a wrong without and fluctuation or variance? Assembly line work?

I come from a family of scientists and mathematicians where creative risk taking is encouraged and failure is expected. It tends to make for a more enjoyable life and a more interesting and lucrative career.

Absolutely, I agree completely, I was always VERY creative in Math....just never got the same answer twice. On the stuff they were trying to teach me, that was a problem. I was in my 30's before it occurred to me that 4 x 8 is 32 EVERY TIME! With my kids I have never encouraged anything but creativity... kid one....high school Spanish teacher, kid two....psychology major, philosophy minor... (under-employed but in earnest quest for the perfect party...lol)....kid three, grad student in OSU optometry department....numero 4 is only 16 but wants to study physics... ( I tell her about the BIG money it that field....hehehe)

There are usually many ways to get to the right end/solution to most problems, I understand that. Striving for perfection is a goal, shooting for just good enough.....well....not good enough for me. I understand I cannot demand perfection of anyone but myself, I have enough friends who tried and lost that battle ..(and wives and kids........)

Even kid two is striving for perfection!!!!!

I did my job.....


back to the thread, after very careful measuring and calculation, my chainline is almost exactly 42 mm both front and rear...It really would have been easy enough for Specialized to put the ring where it should have been at the assembly point. In this case it was an oversite that did make it into the final product. (like Microsoft products, although, I have no real problem with them, they do what I need them to do)
 

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Touch0Gray said:
study physics... ( I tell her about the BIG money it that field....hehehe)
Ah yes, my major before I switched to math. I then went on to get my masters in Art... the big bucks. Now I'm in a job that didn't exist when I was in college using a little of each. Sounds like you've got a great family.

42.5mm is generally the standard for track chainlines. Sounds like you got it all worked out. Looks like Specialzied could use a better QC department; I've got one and they make me look way better than I am.
 
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