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Discussion Starter · #1 ·
I recently bought a bike from Nashbar using a 20% off code. I'm just getting into doing my own maintenance and thought this would be a good opportunity to learn while I assemble it. The bike came with a 12-25 (10 speed) cassette and compact crank. The rear derailleur is a 105 which from what I've read should accept up to 30t. Our area is pretty hilly so I ordered a 12-30 and put it on. I also got a new chain and measured it using the "two biggest rings" method. OK. New chain and cassette are on. Feeling good. Now I think I have to check my limiter screws. That's where the good times end. When I'm in the big ring in the front, I can't shift to the two biggest gears in the back. If I'm in the biggest in the rear and small up front, shifting the big front ring causes the chain to get stuck half on the ring and everything seizes up. Can't turn the crank. I know cross chaining is frowned upon (but maybe less so with a double?), but this can't be normal. So where did I go wrong? Chain too short? Misread the 105's capacity? Thanks.
 

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NOt all 105's accept a 30T. the 5700-A is a 30T RD.

the standard 5700 accepts 28T max.
 

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'zackly. Whatever method you used to size the chain, you did it wrong. You're lucky you didn't force it when trying to shift to the big ring, or you'd break your derailleur.
 

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Discussion Starter · #5 ·
Thanks for the replies. How do I determine the rear derailleur capacity with certainty? The spec list for the bike just says 5700, but on the derailleur is printed RD-5701. And does anyone have a sure-fire method of measuring a chain?
 

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Thanks for the replies. How do I determine the rear derailleur capacity with certainty? The spec list for the bike just says 5700, but on the derailleur is printed RD-5701. And does anyone have a sure-fire method of measuring a chain?
yes, the 5701 is the "A" version

one of the ways to length out a chain is the large & large plus 2 links (if half link, go to the next one).
 

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the SAFEST way to determine chain length is small/small, w/ just enough tension so the lower run of chain doesn't rub on the derailleur cage. this will give the longest possible chain for your derailleur...so if you're within the spec for chain wrap capacity, you will always be able to go big/big. most good mechanics will always size chains this way, unless they're working w/ a single chainring set-up.
 

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Discussion Starter · #8 ·
cxwrench I can't find anything about the method you've described. Do you have a link to a video or something? Every tutorial I've found seems to use the "large + large" method (which is what I thought I did in the first place).
 

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I too always use small-small method. Here are pictures of how the RD should look at either extreme:

Big-Big (worst case)

View attachment 279999

and small-small (with just a little tension on the chain)

View attachment 280000

If OP has really farked things up it might be better to start again with a new chain. Use one with a removable link like Wipperman, SRAM, or KMC, and go easy on the shortening till you get it right.
 

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Thanks for the replies. How do I determine the rear derailleur capacity with certainty? The spec list for the bike just says 5700, but on the derailleur is printed RD-5701. And does anyone have a sure-fire method of measuring a chain?
You were able to shift onto the largest cog (while on the small ring, of course). That suggests your der handles that cog okay. Put some links back into the chain and you should be okay.
 

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In case you didn't know.....Shimano chains are uni-directional and the letters on the links should be facing out. I'm not suggesting that's the cause of the problems you mentioned but figured it was worth a mention. I've fcked that up even with the benefit of knowing they need to go on that way.
 

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One further thought, and perhaps someone more familiar with this Shimano RD will add to it:

OP you are wrong to assume that the fact that the RD should be OK for 30T, means that it will work with all combos of gearing. The 30T max simply means that the upper pulley should clear a 30T cog. The other important issue is the total amount of chain that the RD will take up, and that is determined by the length of the cage.

My illustrations showed a Campy short cage RD illustrating that a 30 tooth TOTAL takeup was about max for that RD. Takeup means the difference between the biggest and smallest cogs plus the difference in the front chainrings.

My pictures showed a 12-26 cassette (14T difference) on a compact 50-34 crankset (16T difference), so 14+16=30T total takeup.

This is a long way round of saying that a short cage shimano RD might not handle the talkeup that you are asking of it which is 12-30 (18T) plus 50-34 (16T) or 34T total.

The way to handle this SAFELY is to size for the big-big combo, and avoid cross chaining in the small ring.
 

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Discussion Starter · #13 ·
Well I couldn't find anything about the 5701 on the Shimano website, but if I'm reading it correctly, the info seen at this link <Shimano 105 5701 10 Speed Rear Mech | Buy Online | ChainReactionCycles.com> suggests I should be good and it is a chain length issue after all. No?

The chain is a KMC. If all I need to do as add a few links, can I just get another missing link and use that (plus the links I had previously removed) to lengthen the chain?
 

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One further thought, and perhaps someone more familiar with this Shimano RD will add to it:

OP you are wrong to assume that the fact that the RD should be OK for 30T, means that it will work with all combos of gearing. The 30T max simply means that the upper pulley should clear a 30T cog. The other important issue is the total amount of chain that the RD will take up, and that is determined by the length of the cage.

My illustrations showed a Campy short cage RD illustrating that a 30 tooth TOTAL takeup was about max for that RD. Takeup means the difference between the biggest and smallest cogs plus the difference in the front chainrings.

My pictures showed a 12-26 cassette (14T difference) on a compact 50-34 crankset (16T difference), so 14+16=30T total takeup.

This is a long way round of saying that a short cage shimano RD might not handle the talkeup that you are asking of it which is 12-30 (18T) plus 50-34 (16T) or 34T total.

The way to handle this SAFELY is to size for the big-big combo, and avoid cross chaining in the small ring.
the Short cage (SS) of the 5701 (5700-A) has a chain wrap capacity of 34T
 

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the Short cage (SS) of the 5701 (5700-A) has a chain wrap capacity of 34T
Good news, and just what OP needs to know.

So, OP what this means is that if the chain is at the correct length, you should be OK in all combos and the RD at the 2 extremes will look like the one in my pictures.
 

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cxwrench I can't find anything about the method you've described. Do you have a link to a video or something? Every tutorial I've found seems to use the "large + large" method (which is what I thought I did in the first place).
In this case, it's actually better to use the big/big plus 1 inch method. If the links that meet when wrapping the big/big are the same - both outer plates - then you should add 1-1/2 inches or 3 links, so the ends can be joined. If the chain does not hang loose in the small/small then the RD's wrap capacity has not been exceeded.
 

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cxwrench I can't find anything about the method you've described. Do you have a link to a video or something? Every tutorial I've found seems to use the "large + large" method (which is what I thought I did in the first place).
What's to figure out? You put the chain on the small ring and the smallest cassette cog (through the derailleur) and then remove just enough links so that the rear derailleur starts to take up slack or so that the chain is not touching the underside of the pulley cage.

Small/small is what is recommended by Campagnolo and has been standard mechanic practice for at least 40 years. Using the "big/big" method suggests that you're using a derailleur with insufficient wrap capacity and so have to make the chain extra long to compensate. If that is the case the chain would be hanging loose in the small/small combination. In practice the big/big approach results in a shorter chain than the small/small in most cases.
 

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