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Chain Length - Help!

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Chain Length - Help!

Old 01-27-21, 04:46 PM
  #26  
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Originally Posted by Gasman1440
P.S. yes there is a formulae for virtually everything....so says the engineer
Unlike many here, apparently, that you're an engineer is not a reason to scoff...might be a similarity we possess.

Read my post above, you don't need a formula. Just a browser, and a few key pieces of data. Plug in the numbers, you'll have your chan length.
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Old 01-27-21, 04:57 PM
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Originally Posted by Badger6
Unlike many here, apparently, that you're an engineer is not a reason to scoff...might be a similarity we possess.

Read my post above, you don't need a formula. Just a browser, and a few key pieces of data. Plug in the numbers, you'll have your chan length.

Thanks....I did and its very helpful. This thread has been very informative for me as I said I’m really new to trying to fix a bike. I like my LBS and they have been helpful but I’m slowly buying a tool here and there and converting to tubeless and changing a cassette etc. Not close to trying to build a bike or fix something that is broken (did I say I’m not mechanical despite being a ME) but I like to learn new things, love to ride and find it almost meditative working on my bikes (or trying to)!
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Old 01-27-21, 05:05 PM
  #28  
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Originally Posted by HillRider
One more time. The manufacturer's recommendations are based on your staying within their published limits for all parameters like max and min cog sizes, chainring sizes and total teeth. If you go outside their limits, you better be willing to adjust as needed.
Well the OP didn't say they were going outside spec. But your suggestion of big big +1 does happen to be what Shimano typically recommends for a 2x road bike setup. At least if that is without threading through the pully wheels.

Though most people going out of spec will be going for larger rear cog and I'd actually worry more about the slack when in the smalls in that case. But whether any DR can do less than big big + 1 I've never tried. And if going out of spec, I'd not go strictly by any mfr suggestion or rule of thumb. I just look and see what the results are. Probably by starting with the chain a link or so longer than the mfr suggestion.
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Old 01-27-21, 06:09 PM
  #29  
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Originally Posted by HillRider
And, no, you don't need a PE if you work for a corporation as your covered by your employer. You only really need it in private practice.
I dunno if that's universal. We (municipal utility/government) have to have our plans stamped by a WI licensed PE. Our chief design engineer stamps in house and whomever involved does consultant plans.
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Old 01-27-21, 07:25 PM
  #30  
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Originally Posted by Gasman1440
Thanks....I did and its very helpful. This thread has been very informative for me as I said I’m really new to trying to fix a bike. I like my LBS and they have been helpful but I’m slowly buying a tool here and there and converting to tubeless and changing a cassette etc. Not close to trying to build a bike or fix something that is broken (did I say I’m not mechanical despite being a ME) but I like to learn new things, love to ride and find it almost meditative working on my bikes (or trying to)!
I think this will broaden your ME "legs".
Simply observing the machinations of a RDER in all the gear combinations can give one an appreciation of engineering.
Having a severe lack of formal education via Asperger's and a 9th grade Algebra teacher that didn't know the Quadratic equation pretty much derailed me. (she was also the principal, so nowhere to complain)
I personally enjoy a well built built wheel. Spoke tensions all equally sharing their part of the load in an artistic symmetry. My "art" tends to be simple mechanical designs that work well.
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Old 01-27-21, 08:38 PM
  #31  
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I get so tired of arrogant engineers. I mean, seriously -- how hard can it be to drive a train? Damn thing is on a track.
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Old 02-16-21, 09:43 AM
  #32  
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Originally Posted by MudPie
on the above Park Tool Page, #6 offers an equation for determining chain length. As an engineer, I also appreciate formulas.
So i should have been more specific in my question. I currently have a new SRAM Red chain that i counted to be 55 full links. It’s on a 10-28 cassette with a 48/35 crank which calculates to be a 53 full link chain. I would like to swap for a 10-33 or 10-36 cassette and am wondering if I need a new chain. My chain stay is 410mm so when i check various ways I come up with needing a chain with 55 (54.339) full links for the 10-36 and 54 for the 10-33 (actually 53.6).

So will a 55 link work with the 10-33 as it has one spare?

Will 55 work with the 10-36 if there is less then one spare?

I’m still trying to see if the Red RD will work with the 10-36, SRAM says no only the 10-33 but several people have said it will work with the 10–36, if anything you may need a longer B-screw. I have some credit and can get the 10-33 Force cassette easily but would love the 10-36. I refuse to buy a new derailure however if that’s what’s needed for a 10-36. Any thoughts, comments answers are greatly appreciated as I’m trying to learn.
Txs
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Old 02-16-21, 10:08 AM
  #33  
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Sometimes I feel like an analogue man who has been trapped in a digital world.

Big/big, bypassing the derailleur and figure out the shortest place you could rejoin the chain. Add 1 inch to that. Takes about the same amount of time as it took me to type this. The digital engineering types will still be counting sprocket teeth.
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Old 02-16-21, 12:00 PM
  #34  
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Originally Posted by Retro Grouch
Sometimes I feel like an analogue man who has been trapped in a digital world.

Big/big, bypassing the derailleur and figure out the shortest place you could rejoin the chain. Add 1 inch to that. Takes about the same amount of time as it took me to type this. The digital engineering types will still be counting sprocket teeth.
No not stuck, I too love my mechanical cable brakes on one bike, have VCR, vinyl and 8 tracks....but I also love my XM radio and DI2 on my ebike. Everyone keeps saying big-big + but if you dont have the chain in your hand how do you know? I’m trying to decide if I need a new chain and I dont have the cassette yet. I cant do big-big because I’m trying to decide which cassette to get (10-33 or 10-36) and then if I need a new chain. So first I have to understand the small intricacies of chain fitting. I’m new to fixing bikes and have very limited mechanical ability but like to learn. I have the tools and ability to change a cassette but dont know enough about is less then one spare link in the chain ok (e.g. the calc is 53.xxx and my chain is 54). So I’m trying to learn from all you more experienced people out there. The Park equation (and several others) is very helpful to figure out what you might need). Yes I could order a new Force chain for $30 and when it comes if I dont need it return it but I’d like to know why you need some amount of slacks but not to much and what amount some is and what is to much. I didnt grow up fixing things so I’m learning all this about bikes in my late 50’s.

Plus, I’m trying to learn if I really can use the 10-36 with my RD. SRAM says no but a few people have said defiantly. So I’m trying to understand how you know if your RD is stretched to much (obviously if the b screw is maxed and your hitting thats a no go). I can not tell from hours of looking at pictures and video of what an extended RD is compared to an ok one. Yes I can go to a great LBS that have helped me a lot and thought me but I’m trying to learn more on my own. I never will put an LBS out of work nor do I do everything online and ignore them, there is a place for both. I’m just trying to learn about bikes and I think for some people who it comes easy its hard to explain to someone like me.

Thanks for any help.
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Old 02-16-21, 12:09 PM
  #35  
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I ALWAYS go with the manufacturer's spec for derailleurs. If SRAM says 33, then 33 it is. I ALWAYS size chains on the bike. Formulas and counting links are a waste of time. If you want to use a 10-36 get the new derailleur that's designed for it. In the past I've used the small/small method as it gives you the longest (safest) chain length as long as all parts of the drivetrain are with the spec for the rear derailleur. Some of the new mtb drivetrains need slightly shorter chains so I use the recommended method from the manufacturer. In other words, RTFM and do what it says. Don't worry about over-extended derailleurs. Don't overthink chain installation.
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Old 02-16-21, 12:17 PM
  #36  
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Originally Posted by cxwrench
Formulas and counting links are a waste of time. In other words, RTFM and do what it says. Don't worry about over-extended derailleurs. Don't overthink chain installation.
I couldn’t disagree more....its not a waste of time, its another way to learn. If your a mechanic perhaps your one of those people that can “do” many things but cant explain how. I know I can do it on the bike but if I dont have the cassette so how do I know if I need a new chain? Yes, $30 will not break the bank but teach me how to fish dont give me a rod and a manual. I’m trying to learn why things are the way they are, perhaps some dont care, I do. I like to learn and question why something is a certain way.

Also, I did RTFM and it doesn’t tell me anything about what I am asking. I could go to bicycle mechanics school or work at the LBS but I cant do that and support my family. I cant believe how many people try to tell me, stop trying to learn, equations are a waste of time, it takes more time to write the question, just do this or do that. Well if you dont have parts bins and tons of chains laying around you want to learn how to do things from the very beginning. Maybe someday I will be able to build a bike, I dont know but I would like to know how you figure things out in advance of buying them.
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Old 02-16-21, 12:20 PM
  #37  
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1) If you're changing the cassette, there's no drawback to putting on a fresh chain. In fact, if your current chain is worn, you'll have poor performance with the new cassette and will likely wear that out prematurely. So when in doubt, I will replace both. Keep in mind that these are both consumables, so you're going to need new ones eventually and you might as well get them both now.

2) You don't have to know the exact number of links when you order the chain. They typically come longer than you need. After you size it, you use a chain breaker to cut off the extra links, then install the quick link attachment. (Remember that the quick links are outside plates, so make sure you're left with two inside half-links on both ends.) So, while calculating the exact number of links is an interesting math problem, it's not necessary to go through that exercise. All the chains on my bikes fit, and I have absolutely no idea how many links are in each.
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Old 02-16-21, 12:25 PM
  #38  
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I understand, the chain I have is brand new. I just got the bike and its my first real road bike hence the questions. The two rides I did told me (I rode about 3k miles last year) a smaller gear will increase my enjoyment significantly. I dont race or ride with others so it’s simply about enjoyment. I have had enough bikes now (mostly gravel and MTB but some road) to know I would have more fun with a lower gear. So really I am just trying to learn....in the future I’m sure I too wont know the links but for now I would like to learn and then decide. Not having the chain or cassette in hand I wanted to learn why you need an extra 1” to 2”, then figure out about what length I need for either cassette I am looking at and decide if I need a new chain.

Basicly I’m trying to do two things, learn about bikes and see if the existing brand new chain will work on either of the cassettes. First and foremost I’m just trying to learn a little, thats all.
Txs
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Old 02-16-21, 12:28 PM
  #39  
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Originally Posted by Gasman1440
I couldn’t disagree more....its not a waste of time, its another way to learn. If your a mechanic perhaps your one of those people that can “do” many things but cant explain how. I know I can do it on the bike but if I dont have the cassette so how do I know if I need a new chain? Yes, $30 will not break the bank but teach me how to fish dont give me a rod and a manual. I’m trying to learn why things are the way they are, perhaps some dont care, I do. I like to learn and question why something is a certain way.

Also, I did RTFM and it doesn’t tell me anything about what I am asking. I could go to bicycle mechanics school or work at the LBS but I cant do that and support my family. I cant believe how many people try to tell me, stop trying to learn, equations are a waste of time, it takes more time to write the question, just do this or do that. Well if you dont have parts bins and tons of chains laying around you want to learn how to do things from the very beginning. Maybe someday I will be able to build a bike, I dont know but I would like to know how you figure things out in advance of buying them.
The manual can't tell you how many links you need...how could it? It most definitely DOES tell you how to properly size the chain. You need to have the parts you want to use on the bike to do this. If you're putting a new cassette on just put a new chain on as well. They ALL come long and you'll have to remove some links.
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Old 02-16-21, 12:38 PM
  #40  
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I have grown to like the small/small sizeing approach no calculations needed

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Old 02-16-21, 05:54 PM
  #41  
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Originally Posted by Gasman1440
Everyone keeps saying big-big + but if you dont have the chain in your hand how do you know? I’m trying to decide if I need a new chain and I dont have the cassette yet. I cant do big-big because I’m trying to decide which cassette to get (10-33 or 10-36) and then if I need a new chain. So first I have to understand the small intricacies of chain fitting. I’m new to fixing bikes and have very limited mechanical ability but like to learn. I have the tools and ability to change a cassette but dont know enough about is less then one spare link in the chain ok (e.g. the calc is 53.xxx and my chain is 54).
The big-big + 1 method: the "+1" is needed to allow the chain to climb over the teeth of the chainring or the cog when shifting to the big/big combination. Otherwise the chain will jam, and the tension will mangle the RD and the hanger. Instant disaster you do not want to happen. It is not about stressing the RD pedaling in this combination, but about it being destroyed during shifting. Check it on a stand first, gently rotating the pedals by hand.

Many years ago when I had no clue about bike mechanics I destroyed an old Sears FreeSpirit this way. I shifted to the big-big, simultaneously in the front and the rear. The chain was not properly sized.

I you do not have the cassette you can use the Park formula, or this calculator: Javascript Bicycle Chain Length Calculator (the latter does not add +1", you need to do it yourself; they also speak about adding +2" for RDs with large wheels, this is not correct, +1" should be enough).

Exceeding the B-screw capacity/specs for the large cog is a different story.

Last edited by csport; 02-17-21 at 03:21 PM.
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Old 02-17-21, 05:56 AM
  #42  
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Originally Posted by Gasman1440
I understand, the chain I have is brand new. I just got the bike and its my first real road bike hence the questions. The two rides I did told me (I rode about 3k miles last year) a smaller gear will increase my enjoyment significantly. I dont race or ride with others so it’s simply about enjoyment. I have had enough bikes now (mostly gravel and MTB but some road) to know I would have more fun with a lower gear. So really I am just trying to learn....in the future I’m sure I too wont know the links but for now I would like to learn and then decide. Not having the chain or cassette in hand I wanted to learn why you need an extra 1” to 2”, then figure out about what length I need for either cassette I am looking at and decide if I need a new chain.

Basicly I’m trying to do two things, learn about bikes and see if the existing brand new chain will work on either of the cassettes. First and foremost I’m just trying to learn a little, thats all.
Txs
Playing around with the calculators is fine, and one day I might do the same. However, if you are trying to create a combination which is not recommended you risk falling outside what the calculators are designed to do. I am not saying that should be a barrier, because as an R&D engineer I would write the specs to keep the company from legal/guarantee consequences and the potential negative consequences of future developments, not to define what was possible.

Don't worry about the chain length now - get the new cassette you clearly want and see how your current new chain fits. Development begins with many theories, but until you have something to test the theories are nothing but theories. Testing is where we learn to understand.
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Old 02-17-21, 08:52 AM
  #43  
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Originally Posted by Geepig
Playing around with the calculators is fine, and one day I might do the same. However, if you are trying to create a combination which is not recommended you risk falling outside what the calculators are designed to do. I am not saying that should be a barrier, because as an R&D engineer I would write the specs to keep the company from legal/guarantee consequences and the potential negative consequences of future developments, not to define what was possible.

Don't worry about the chain length now - get the new cassette you clearly want and see how your current new chain fits. Development begins with many theories, but until you have something to test the theories are nothing but theories. Testing is where we learn to understand.

Agree, the calculation was only to see if I needed to order the new chain, and for my own learning. I see the drawings and videos and I cant really tell when they show a RD thats to tight vs not.....I’m not good at that! I also do not want to screw up this bike, I have other bikes that are more suitable for experimentation. I think the 10-33 is the way to go for now and given there still is snow on the ground I can always order the chain after I install the cassette. I also didnt know how to determine if my existing chain is ok with the new cassette. For example, if I do big big and its 13/16” of an inch, thats not an inch but probably ok. What if its big big and only 1/4”? I was trying to understand all that as well. So it was a combination of experimentation (10-36 even though SRAM says 10-33) plus learning (is big big plus 1/4” ok)?

Txs
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Old 02-17-21, 10:22 AM
  #44  
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Seems like you're making this too difficult. The simple equation really is simple. It's just twice the chain stay length plus the total of maximum wrap divided by 4.

One thing to keep in mind is that it requires 4T of additional sprocket to use an entire inch of chain. If you change from a 33 to a 36 max sprocket, it will most likely need an extra inch of chain, unless your current setup has an additional 1/4 of chain length to spare. That's where the formulas come in handy, but only if you know the exact chain stay length. Another thing to remember is that the big/big plus 1 inch method is the minimum length needed. If 2 inches are added, the worst that can happen is the lower section of chain will hang loose in the little/little combo. If you're using SRAM AXS, it's best to start with the chain too long and only remove 1 inch if needed. I've reused the AXS quick links many times and not had a problem, but I also keep extra links on hand. If it makes you nervous to reuse a link, sacrifice one and mark it for the next time you need to test a chain length. Any old 11 speed link will also work, just for a test on the work stand. I have one that I use, just for this purpose.

If the chain length is set for a 36T sprocket, it is not necessary to shorten the chain to use a 33T max sprocket. The B screw position should be adjusted though.

FWIW, with 415mm chain stays, a 54 inch chain will barely wrap a 46 chain ring and the 36T sprocket. The simple equation yields a 54.17 inch calculated length. Park says to round down if the result is less than 54.5. I use a 55 inch chain, because the equation suggests more than 54 inches with 415mm stays and a 46/30 crank. Only the 30/11 combo is too loose to use, but I never go smaller than the 13. I can change to a 48/32 crank with the same chain length and not have to worry about it being too short. The absolute maximum wrap capacity of any derailleur depends on the chain stay length. A perfect length will have 3T more wrap than the worst case. The advertised wrap capacity has to account for the worst case length, where 1 inch of chain length is added, just to cover the need for 1/4 inch.

For those who don't know how many links are on their chain, lay it out on a table and measure the entire length, between pin centers, including the quick link. A 55 inch chain has 110 links, since the chain pitch is 0.5 inch. There is never a need to count links.
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Old 02-17-21, 03:19 PM
  #45  
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Physics major here.
Originally Posted by Gasman1440
Agree, the calculation was only to see if I needed to order the new chain, and for my own learning. I see the drawings and videos and I cant really tell when they show a RD thats to tight vs not.....I’m not good at that! I also do not want to screw up this bike, I have other bikes that are more suitable for experimentation... I also didnt know how to determine if my existing chain is ok with the new cassette. For example, if I do big big and its 13/16” of an inch, thats not an inch but probably ok. What if its big big and only 1/4”? I was trying to understand all that as well. So it was a combination of experimentation (10-36 even though SRAM says 10-33) plus learning (is big big plus 1/4” ok)?
Txs
You can become good at that easily Of course you can read the manuals, but it is better to understand what the manual is trying to prevent. I think I answered the question is post #41, here is and older post by FBinNY explaining this: https://www.bikeforums.net/19651934-post3.html He is a pro mechanic with a huge experience very highly respected here.

Is 1/4" OK? If we assume the worst case scenario when the chain does not shift right away but rides on the tops of the teeth for some time, what is the extra length needed? I apposed the measuring tape to the chainring, the tooth height is approximately 6mm. The extra length of the half circle is then pi*6mm = 19mm. This is more than 1/4", 13/16" will barely suffice. You may get away with it, and the best way to check is to test on the stand. I would not do it, and there is a good reason people say 1":

Another story is what happens if you shift in the front and the rear simultaneously. This is how I destroyed an old clunker long ago.
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Old 02-18-21, 12:45 PM
  #46  
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All of my bikes have always been triples. I don't know if these triples have anything to do with it, but all of the above methods have never worked for me. So I use a decidedly non-formulaic, probably cumbersome, but always foolproof method.

I keep old chains for sizing purpose, one 8 speed and one10 speed for my different drive trains. I leave the chain pins in on one side of the broken link of these chains. I also have supplies of discarded links and pins. When I need to size a chain, I install the appropriate old one, removing or adding links until the fit is right. Then I match the length of the new one to that of the old one.

I doubt if too many other people use this method, but it works for me.
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Old 02-18-21, 01:52 PM
  #47  
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The methods mentioned work perfectly with a triple crank, providing that you're not exceeding the RD wrap capacity. If that's done, then using the big/big plus 1 inch or formula methods may result in the chain being loose in the little/little combo, but there's no point in using the little ring and the smallest several sprockets.
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Old 02-18-21, 03:52 PM
  #48  
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Originally Posted by MudPie
on the above Park Tool Page, #6 offers an equation for determining chain length. As an engineer, I also appreciate formulas.
As a boilermaker I find engineers to be a pain in the butt.
Shimano at one time that the pullies should be verticle when the chain is on the big ring and small cog.
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Old 02-18-21, 03:55 PM
  #49  
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Originally Posted by DaveSSS
I got my mechanical engineering degree from Kansas State University, in 1981, at age 28. After that, I spent 22 years working in a nuclear weapons manufacturing plant, with up to 6000 employees. A PE license was not a requirement to develop manufacturing processes for nuclear weapons components. I quit that job to follow my wife's more lucrative job, working for the US Treasury Department. Finding an equivalent position at age 50 proved impossible, so I retired, 18 years ago.
I retired before my wife also and became her house-ho!
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Old 02-18-21, 04:06 PM
  #50  
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Originally Posted by DaveSSS
The methods mentioned work perfectly with a triple crank, providing that you're not exceeding the RD wrap capacity. If that's done, then using the big/big plus 1 inch or formula methods may result in the chain being loose in the little/little combo, but there's no point in using the little ring and the smallest several sprockets.
Yeah, I don't want the chain loose; it slaps the chain stay if I accidentally drop into that gear. I just finished using my method described above to install a chain on my 1979 Richard Sachs. The chain is perfect in every gear.
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