Is a long cage derailleur required for 1x11 11-40 cassette? Sram Force 1

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AJS914
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Joined: Tue Jan 28, 2014 6:52 pm

by AJS914

I'm converting an Sram Force 1 CX setup for gravel/adventure riding. Currently I have 44x11-32 with a mid-cage rear derailleur. I'd like to run 38x11-40. Sram's page says that their long cage rear derailleur is compatible with the larger cassette.

I'm trying to think through why you need the long cage for a 1x drivetrain. They say to size the chain by putting it on the chainring and the largest rear cog and then add 4 links. How does the length of the derailleur cage make any difference with 1x?

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oldnslow2
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by oldnslow2

I have Rival 1 CX and when from a short to a mid when i swapped 11-28 cassette to a 11-32. From what i've ready the mid is good to a 11-36 so i would assume you need a long for a 40.

https://www.sram.com/sram/road/products ... derailleur

"Available in Short: 11-26 through 11-28 / Medium: 11-26 through 11-36 / Long 11-32 through 10-42 cage Lengths"

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AJS914
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by AJS914

Yeah, I know that is what they say. I'm kind of wondering the why of it. There's no small chainring where chain slack needs to be taken up. The procedure for setting the chain length is exactly the same. They don't say to add more lengths for a long cage.

Unless someone tells me that it is dangerous, I may just try the med cage derailleur I have and see how well it works.

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oldnslow2
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by oldnslow2

That is true... if you have a 1x then you don't have to take up the slack from a 50T or 53T large chainring.

I could take a picture of the chain on the 32T cog.

Image

AJS914
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by AJS914

Here is what she is looking like now. I need to sell off the wheels because I can't ride tubulars and fit a 12cm stem instead of the 15 that is on there. Plus I'll do the gearing changes.

Image

stk57

by stk57

AJS914 : What BB and crankset are these ? Which BCD ? Can it fit Rival 1 rings ?

BB30 with or whitout any washer/spacer to accomodate a XX1 crankset to the CX chain-line ? Don't know if it's needed compared to a 1x MTB chainline the XX1 is commonly found.

Or a simple Red crankset without the inner chainring ?

I'd like to convert my 2017 Allez DSW Sprint 2x Comp to a 1x crit bike and I'm in the process of finding the right crankset+ring combination to get full use of the 11 cogs from a solo ring up front. Hence my many worries and questions.

-STK-

RussellS
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by RussellS

Seems to me the rear derailleur should only be concerned about the total chain wrap. 40-11=29. I think short cage rear derailleurs handle 28 tooth chain wrap. But pretty sure going to 29 would not be a problem. Potential problem may be whether the rear derailleur can swing under the big cog. Might be a slightly different swing under the big cog between short and long cage rear derailleurs. Do you have access to an extra long rear derailleur hanger? I find it hard to believe any derailleur can fit under a 40 tooth rear cog.

Your question: "How does the length of the derailleur cage make any difference with 1x?"
The derailleur cage takes up chain wrap. Whether the wrap comes from the difference in chainrings or difference in cogs makes no difference. It all adds up to affecting how much the rear derailleur swings back and forth. Front to back.

Not sure why SRAM says to add 4 chain links when on the big-big combination. Seems way too much. Big-big with rear derailleur straight ahead. Then add one full link.

grover
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by grover

SRAM 1x derailleurs only move sideways. They have no up and down movement. This contributes greatly to their chain retention abilities and the decreased noise.

Somehow the top jockey wheel needs to move up and down to follow the contour of the cassette. To achieve this without the derailleur body moving up and down they have offset the top jockey wheel from the rotation point of the cage.

As you shift through the gears the bottom jockey wheel moves back/forward to take up the chain slack. The cage length to the bottom jockey wheel determines how much vertical movement the top jockey wheel has.

So a short cage derailleur might be capable of taking up the chain slack through the range of the cassette, but the top jockey wheel will not follow the cassette contour correctly if you use the incorrect cage length for your desired cassette range. You will be choosing a trade off between the jockey wheel getting too close to the easy (big) cogs or too far away from the hard (little) cogs. So you will always be left with poor shifting in ~30percent of the cassette.

This is a little dependent on derailleur hanger length and geometry too. Some frames might get away with it better than others.

Sidenote: this is also why 1x derailleurs don't work on a double chainring. The derailleur cage might take up the chain slack between chainrings, but the change in chain length will totally destroy the position of the top jockey wheel under the cassette and will shift horribly (actually unusable).

Chain length: Correct sizing with a SRAM 1x derailleur is big-big + 4 links as stated. This sets correct jockey wheel position with cassette size appropriate for selected cage length.

Short cage: 26 to 28 big cog
Medium cage: 26 to 36 big cog
Long cage: 32 to 42 big cog

AJS914
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by AJS914

Grover, thanks for explaining that. Now I get it and now I understand why the mountain bike guys were talking about using med and short cages derailleurs on 1x setups. I guess I will source a new rear derailleur to make it all work.

Or a simple Red crankset without the inner chainring ?


Yes, I believe that it is a Red crankset with an SRAM xSync chainring. I checked the chainline and it looked spot-on. I don't know what spacers are involved.

Honestly, I kind of wish this bike was 2X but I'm going to keep it 1x and give it a go. To switch to 2X I'd need new shift levers and these hydro levers and brakes cost around $700 a set. I have 1X gearing on my Specialized Camber and I'm not sure I like it. It works fine I always feel like I'm missing a gear at the high and the low ends.

RussellS
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by RussellS

AJS914 wrote:I have 1X gearing on my Specialized Camber and I'm not sure I like it. It works fine I always feel like I'm missing a gear at the high and the low ends.


Yes. With a single chainring, you are likely to pick something mid way between the outer and inner rings. You said "Currently I have 44x11-32 with a mid-cage rear derailleur." If you were running a double crank with 53-39 rings, then you would have more highs and more lows. Your first post said you want a 38 ring with an 11-40 cassette. So you are giving up some on the high and getting a bit more on the low side. You could easily get a double crank to provide the same gear range as your 38 x 11-40 combo. A 44-34 compact crank with 11-34 cassette gets you about the same gear range. But the big disadvantage of the single speed is you must accept big jumps in the gears to end up with a similar range. Your choices are same gear range with big jumps in gears. Or keep same jumps in gears but give up the big and low gears. You can't have cake AND ice cream. You got to pick either cake OR ice cream. Not both.

AJS914
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Joined: Tue Jan 28, 2014 6:52 pm

by AJS914

Well, I'm converting this from a cyclocross to a gravel setup thus I want more low gear. I'm willing to sacrifice high gear.

I'd love to switch it to a double but a new set of hydro levers costs a small fortune so I'm just going to stick with 1x and try 38x11-40 for now.

grover
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Joined: Mon Jul 26, 2004 1:06 pm

by grover

I have a bike with Force 22 mechanical brakes, and a bike with Force 1 hydro brakes.

I want the mechanical bike to be Force 1 and the hydro bike to be Force 22. Therefore I'm going to see if I can take the shifter guts from the left mechanical level and put them in the empty left hydro lever. I'll let you know if that works.

Then you can trawl ebay for a cheap left mechanical shift lever and use the shifter guts out of it to make your 1x hydro lever 2x.

by Weenie


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JAWN
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by JAWN

grover wrote:I have a bike with Force 22 mechanical brakes, and a bike with Force 1 hydro brakes.

I want the mechanical bike to be Force 1 and the hydro bike to be Force 22. Therefore I'm going to see if I can take the shifter guts from the left mechanical level and put them in the empty left hydro lever. I'll let you know if that works.

Then you can trawl ebay for a cheap left mechanical shift lever and use the shifter guts out of it to make your 1x hydro lever 2x.

I know this was from a while ago but did it work?

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