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B Screw question

Old 08-08-22, 10:15 AM
  #26  
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Originally Posted by cxwrench View Post
I can't imagine it being explained any better. If you don't understand what is being done in Bill's photo I don't know what to say. One more time...shift the bike into big/big (carefully in case there isn't enough chain) then put the screwdrivers in the chain as shown in the photo. If there's enough slack to do that you're good to go. I just twist the chain w/ my fingers but if you don't want to get dirty use the 2 small screwdrivers. If you need a video to make that more easily understood then watch a video. At that point it should be crystal clear.
I can put the bike in big/big and take up all the slack then release tension until I can gather 1-2" of slack...but then the hanger on the RD would be nearly fully biased forward. That would leave the chain WAY too tight for the bike.
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Old 08-08-22, 11:13 AM
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Originally Posted by sknhgy View Post
I can put the bike in big/big and take up all the slack then release tension until I can gather 1-2" of slack...but then the hanger on the RD would be nearly fully biased forward. That would leave the chain WAY too tight for the bike.
...the way rear derailleurs are supposed to work is that the spring loaded cage has a certain capacity to take up the slack, and tension the chain in all combinations. The only way to get it to work well over this entire range (from big /big to small/ small), is to adjust chain length so the cage is angled forward in the big/big combination. That's how rear derailleurs work.
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Old 08-08-22, 01:49 PM
  #28  
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OK, OK, my bad. When I checked it before taking out the links I could get all kinds of slack. After taking out about 4 links there's hardly any. It rides ok. When this chain gets used up I'll probably add 2-4 links back in.

Thanks for the help everyone.
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Old 08-08-22, 03:48 PM
  #29  
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Originally Posted by sknhgy View Post
OK, OK, my bad. When I checked it before taking out the links I could get all kinds of slack. After taking out about 4 links there's hardly any. It rides ok. When this chain gets used up I'll probably add 2-4 links back in.

Thanks for the help everyone.
Why would you do that?
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Old 08-08-22, 03:58 PM
  #30  
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Originally Posted by bikeme View Post
Almost touching is way too close. I was misled by Shimano instructions of having it very close for years. I've found that 5mm between the largest cog's and pulley's teeth is great. Yields plenty of chain wrap on big cog and quieter drivetrain. Per the attached video, also check the b-tension with the chain in big ring and highest cog so there's no belly in the chain (provided chain is proper length). Kyle is does a great job of explaining what b-tension actually does and how to adjust it! FYI, he's a mtb guy but info applies to road bikes too. EDIT: additional thought--if this is a mtb with an after-market extra big gear, you might need a longer (like 25mm) b-tension screw that the RD originally came with.

https://youtu.be/TGCM2DTsozk
The "B" screw is NOT an tension adjustment!!!
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Old 08-08-22, 04:00 PM
  #31  
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Originally Posted by bikeme View Post
Almost touching is way too close. I was misled by Shimano instructions of having it very close for years. I've found that 5mm between the largest cog's and pulley's teeth is great. Yields plenty of chain wrap on big cog and quieter drivetrain. Per the attached video, also check the b-tension with the chain in big ring and highest cog so there's no belly in the chain (provided chain is proper length). Kyle is does a great job of explaining what b-tension actually does and how to adjust it! FYI, he's a mtb guy but info applies to road bikes too. EDIT: additional thought--if this is a mtb with an after-market extra big gear, you might need a longer (like 25mm) b-tension screw that the RD originally came with.

https://youtu.be/TGCM2DTsozk
The "B" screw is NOT an tension adjustment!!!
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Old 08-08-22, 04:34 PM
  #32  
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Originally Posted by cxwrench View Post
Why would you do that?
IDK. Don't you want a little slack? Because that's what I've got - just a little.
Maybe I won't.
It's ok. I got time to think about it.
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Last edited by sknhgy; 08-08-22 at 04:56 PM.
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Old 08-08-22, 09:59 PM
  #33  
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Originally Posted by sknhgy View Post
OK, OK, my bad. When I checked it before taking out the links I could get all kinds of slack. After taking out about 4 links there's hardly any. It rides ok. When this chain gets used up I'll probably add 2-4 links back in.

Thanks for the help everyone.
Are you saying that when the chain becomes worn out you're going to put 2-4 links back in? Cuz it sounds like that's what you're saying.
Originally Posted by sknhgy View Post
IDK. Don't you want a little slack? Because that's what I've got - just a little.
Maybe I won't.
It's ok. I got time to think about it.
You would put 2-4 links with zero wear back in to a worn out chain? Because you just ran that chain long enough to wear it out...at the proper length...and now you're going to put some links on to the chain that aren't worn at all...and make your chain that much too long? Do you know how stupid this sounds?
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Old 08-09-22, 06:55 AM
  #34  
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I think all sknhgy is saying is that he or she would replace this chain with one that's 1 or 2 links longer when it comes time to replacement, because he or she doesn't like how much tension the current one has in the big-big combination.

sknhgy, while the predominant method of sizing a chain is to use the big-big method to ensure there's just enough slack, I typically favor less chain tension, and I use the small-small method...in other words, make the chain just short enough to where the chain doesn't drag on itself when in the smallest possible driveline combination. This usually leaves plenty of room on the big-big combination. This also results in a chain with less tension than most people prefer, but I don't ride aggressively to where I want that extra tension to help avoid chain slap on the chain stay or for chain retention, etc. I find that, with just a little less tension/more chain length, the driveline is quieter and seems to pedal more smoothly. This, of course, requires your derailleur to be able to clear the big sprocket in low gear...which of course circles back to the original question and response...where shortening the chain just a little bit can sometimes help a situation with marginal clearance.
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