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Code: FW10.ER-10
Extend your 10speed range on your Shimano or SRAM Cassette with this 40/42T Cog.


A great addition to e*thirteens product range, now you can add range to your 10 speed, Shimano or SRAM cassette with this range extender. Simple to fit, all you need do is remove the 15t or 17t cog from your cassette & place the EX Cog on your freehub, then install your existing cassette back in place. Your shifting will remain just as sharp thanks to e*thirteen speed shift technology and the EXA+ anodized aluminium resists flex under heavy power.


  • It's an add-on cog to extend gear range of 10 spd. Shimano and SRAM cassettes
  • It comes in 40t and 42t for use with Shimano cassettes and a 42t only for use with SRAM cassettes
  • Installing your EX Cog is easy.
  • Each EX Cog is timed and ramped specific to Shimano and SRAM cassettes
  • The EX Cog comes with a longer steel replacement, B-limit screw for your derailleurs. Your current one won't be long enough to get the best shifting up to the new cog
  • Cog material:     EXA+ Aluminium
  • Thickness:           5mm
  • Weight: 70g (40t) 77g (42t)


Useful recommendations:

Q: Can I use the 40t EX Cog with a 36t cassette?

A: We don't recommend using the 40t EX Cog with a 36t cassette. Shift performance will be compromised as the timing will not be correct.


Q: Can I use the 42t EX Cog on my 34t cassette?

A: The 42t EX Cogs WILL NOT work with 34t max cassettes. A 6 tooth jump is the maximum for good shifts.


Q: I have a short cage derailleur on my bike. Will that work?

A: We recommend a medium or long cage derailleur. (if you are not sure about max. derailleur capacity, check here to reference our handy compatibility chart.)


Q: Why do you only have a 42t EX Cog for SRAM cassettes?

A: The 40t is available only for Shimano as SRAM is not offering a 34t cassette.


Q: Is it hard to setup the EX cog?

A: It's really not too hard, but you are working at the extreme limits of your rear derailleur. If you have specific questions about the setup and adjustment, we recommend heading to your local bike shop.


Q: I have a really worn drivetrain. Will the EX Cog work ok on my bike?

A: Old drivetrain components could cause poor shifting performance. We recommend a new chain and a new or well-cared for cassette.


Q: What is the extra screw for?

A: It's a replacement B limit screw for your rear derailleur. The longer screw may be needed for proper derailleur set-up. If you are unsure about setting your B limit, refer to our how to guide, or head in to your local bike shop.


Q: Can I run this cog on my 2x system?

A: Indeed you can if you have the proper bits currently in your drivetrain. Please visit our compatibility chart online in our tech area for proper compatibility.

Great product arrived quickly and looks great and makes a big difference up the hills
Great to finally get over those steep ascents! Best of all, it looks really cool too.
works perfect on 36-11, no problems with XT or STR shifter with short 85 mm cage
Works great with a Shimano Xt shadow plus medium cage derailleur. Super easy to install.
Great bit of kit, I had to put a 1mm spacer behind it for use with an XT cassette on DT swiss hubs, but the chain shifts up really smooth, great with narrow/wide front ring and shadow+ mech