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Can you measure Shimano 12 speed rear derailleur length?

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Can you measure Shimano 12 speed rear derailleur length?

Old 12-30-20, 09:54 AM
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ft3safety
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Can you measure Shimano 12 speed rear derailleur length?

Hi,

Hopefully I can reach out to someone with a Shimano long cage 12 speed rear derailleur. If so, could you please measure the distance from where the derailleur attaches to the frame (center of bolt) to the very bottom of the rear derailleur swing arm at 6 o'clock position? Not entirely mountain bike relating but I'm wondering if I can use a wide range cassette (50 or 51 tooth) on a small folding bike (16" wheels / 20" wheels). Or would it be too long and would the bottom portion hit the pavement? My folding bike is a 1x system so having a 1x - 12 speed will really help get good gear ratios.

Thank you!
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Old 12-31-20, 11:51 AM
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There is no measurement or answer to your question.

All rear derailleurs have two basic specs; max cog and capacity.

Max cog is the rating based on design that design to use a 28t, 34t, 40t, 50t, etc. cog. It technically has nothing to do with cage length, but every mfg designs them together because an 11-50 cassette has capacity issues even with a 1x.

Capacity is the amount of extra chain can be stored, so to speak, between the derailleur pulleys (cage length). The the longer the cage the more capacity.

Wolftooth, and others, have an adapter that lowers the derailleur away from the cassette and allows a larger max cog.

But as you noted lowering the derailleur on 16”/20” wheels will probably be a deal breaker. I’m running a Wolftooth RoadLink on my 26er with a 40t and my longe cage derailleur sits 5” off the ground. I’m one bad line away from walking.

If you have a specific derailleur that will run a 50t, you can probably get an answer to cage length question. But overall maximum derailleur vertical “stretched” length might be more important.

John

Last edited by 70sSanO; 12-31-20 at 11:55 AM.
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Old 01-01-21, 03:46 PM
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Originally Posted by ft3safety View Post
Hi,

Hopefully I can reach out to someone with a Shimano long cage 12 speed rear derailleur. If so, could you please measure the distance from where the derailleur attaches to the frame (center of bolt) to the very bottom of the rear derailleur swing arm at 6 o'clock position? Not entirely mountain bike relating but I'm wondering if I can use a wide range cassette (50 or 51 tooth) on a small folding bike (16" wheels / 20" wheels). Or would it be too long and would the bottom portion hit the pavement? My folding bike is a 1x system so having a 1x - 12 speed will really help get good gear ratios.

Thank you!
I have a shimano 1x12 MTB and a 20 folding bike. No need to measure anything. It's going to hit the pavement for sure.

My folding bike uses a SRAM DualDrive, which combines a 3x IGH with an 11-34 cassette, to achieve an extremely wide range. It works great, but I think they stopped selling them years ago.

Sturmey Archer has (or at least had) a similar solution though.
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Old 01-01-21, 06:43 PM
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Thanks Amt0571! I asked a friend with a 12 speed rear derailleur and they told me that from the the center of the axle to the bottom of the rear derailleur swingarm is approximately 24cm on the 12 speed long cage rear derailleur. I measured my 10 and 11 speeds at 21.5cm and 22cm respectively. The dual drives were good but yes I too think they stopped production. My 1x8 with 11-32 doesn't give me the gears I'd like. A 11-51 would be nice...
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Old 01-02-21, 04:13 PM
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Originally Posted by ft3safety View Post
Thanks Amt0571! I asked a friend with a 12 speed rear derailleur and they told me that from the the center of the axle to the bottom of the rear derailleur swingarm is approximately 24cm on the 12 speed long cage rear derailleur. I measured my 10 and 11 speeds at 21.5cm and 22cm respectively. The dual drives were good but yes I too think they stopped production. My 1x8 with 11-32 doesn't give me the gears I'd like. A 11-51 would be nice...
Check if Sturmey Archer still sell the CS-RF3. Its the same concept as the DualDrive.

I think that the idea behind an IGH mated to a cassette is better than a wide range 1x on a 16" or 20" bike, since it allows low gears, but also high gears without needing an enormous chainring.

I'm personally very happy with my DualDrive, and I think it's a shame they stopped selling it.
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