1x RD with 2x FD - Why Not?
08-21-22, 04:22 AM
#1
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1x RD with 2x FD - Why Not?
Hello,
I currently have a 1x SRAM Apex RD with a 1x SRAM Apex 40T crank (GXP BB) and 11-42 cassette on a bike. I want to try 2x on this bike so I bought a SRAM 38/24 crank (GXP BB) for the purpose. Looking at the SRAM website I noticed that the existing Apex RD on the bike is spec'd as only for use with 1x drivetrains.
What might happen if I try to use this 1x RD with a 2x crank and FD?
Thanks!
I currently have a 1x SRAM Apex RD with a 1x SRAM Apex 40T crank (GXP BB) and 11-42 cassette on a bike. I want to try 2x on this bike so I bought a SRAM 38/24 crank (GXP BB) for the purpose. Looking at the SRAM website I noticed that the existing Apex RD on the bike is spec'd as only for use with 1x drivetrains.
What might happen if I try to use this 1x RD with a 2x crank and FD?
Thanks!
08-21-22, 04:41 AM
#2
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The Apex 1 rear derailleur doesn't have the chain wrap capacity to take up the extra slack in the chain when you shift into the small chainring at the front. You have the parts in hand, so it can't hurt to try them and find out.
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08-21-22, 09:18 AM
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There will be some pretty major slack in the chain in the small ring/smaller cogs. Because the rear derailleur doesn't have the chain wrap capacity for a 2X...which is why SRAM specs it for 1X. This set up will not work correctly. You can try it, but it's going to be compromised because it's the wrong derailleur.
08-21-22, 05:12 PM
#4
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Thread Starter
Ok - makes sense re: lack of chain wrap capability.
I found a SRAM GX 2x11 RD that will take a 42T cog - $85 new. It should work with the Apex brifter thanks to 'X Actuation'.
For the FD I'm thinking of using the GRX 400 braze on using a bar end shifter to actuate.
Thanks.
I found a SRAM GX 2x11 RD that will take a 42T cog - $85 new. It should work with the Apex brifter thanks to 'X Actuation'.
For the FD I'm thinking of using the GRX 400 braze on using a bar end shifter to actuate.
Thanks.
08-21-22, 07:26 PM
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'Shifter'.
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01-04-23, 07:37 AM
#7
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jlaw, did you ever try this and confirm the lack of chain wrap capacity for the Apex RD? I want to try the same thing and was curious if it would work.
01-09-23, 07:25 PM
#8
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Thread Starter
I bought a SRAM GX RD, an inexpensive GXP 38/24 MTB crank, and a Rival YAW FD ($20 from Jenson!). I also set it up for friction shifting using some ENE Ciclo bar ends that I already had (need to add an in-line Shiftmate 8 for the ENE bar end to clear all 11 cogs - only clears 9 cogs without the Shiftmate)
I like a nice quiet drivetrain and couldn't get the SRAM RD indexing 100% in all gear combos - friction shifting solved that!
I'm likin' it!!
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01-09-23, 08:31 PM
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There will be some pretty major slack in the chain in the small ring/smaller cogs. Because the rear derailleur doesn't have the chain wrap capacity for a 2X...which is why SRAM specs it for 1X. This set up will not work correctly. You can try it, but it's going to be compromised because it's the wrong derailleur.
This ^^^^^^
1x rear derailleur will not work if go big in the back 11- 40T it's not going to be able chain wrap small and small and have enough chain for BIG and BIG.
It might work if you had a 11-28T or 11-30T on the back.
01-09-23, 09:19 PM
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The Apex and NX are apparently identical except for the way the cable comes in for the different cable pull per shift. The X-Horizon style RD does not have a slant parallelogram. The proximity of the upper pulley to each cog is pretty closely controlled by the chain wrap. In the 11 speed versions it’s 42-46 teeth max, and MTB size shifts. A double front and smaller cassette would screw that up pretty good. Even if you were within the wrap.
If you want a more adaptable RD, Shimano makes one
If you want a more adaptable RD, Shimano makes one
Last edited by Darth Lefty; 01-09-23 at 09:35 PM.
01-10-23, 07:53 AM
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Even if you can get enough capacity, the jockey pulley geometry of many 1x derailleurs is incompatible with 2x because the upper pulley moves drastically to produce cassette clearance. So you'll have good clearance in the big ring, but then with extra chain slack you lose that clearance in the small ring. Or you have too much chain gap in the big if everything is alright in the small. That's why Shimano and Sram make separate 1x and 2x derailleurs.
