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PostPosted: Fri Jan 15, 2010 9:23 pm 
Moderator /Lincs, E & S Yorks Deputy AEC
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Sram & Shimano have different ideas of what is short, medium & long cage.

I run a modern Sram X9 medium cage rear mech with 22/32/44T chainrings & an 11/32T cassette, it works if you use your gear ratios correctly.

Quite a a lot of modern bikes come with a medium cage Sram rear mech

IIRC Sram mechs are longer than Shimano's mech's of the same stated length, capacity is what really matters.


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PostPosted: Fri Jan 15, 2010 9:29 pm 
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was going to ask this

thanks ,really useful

mike


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PostPosted: Sat Aug 14, 2010 8:56 pm 
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found this thread, and although its been a while since it was current, the info has been really helpful. Its all about capacity, so dont hung up whether its short or medium between SRAM and Shimano. Great post thanks and glad its still retrievable!


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PostPosted: Sat Aug 14, 2010 9:06 pm 
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I've alway fancied the idea of short cage mechs just for the look of it.


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PostPosted: Sat Aug 14, 2010 9:18 pm 
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who'd want to use the smaller sprockets with the granny ring anyway ?!


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PostPosted: Sat Aug 14, 2010 9:53 pm 
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This stuff is 'rule of thumb' only, IMO.

Provided that you use the small chainring with the largest sprockets and vice versa, you can get away with a short cage mech for almost anything.

I've used 11-30 (8-speed) with 20/32/42 rings but only used the 20 with the largest 5 rings and the 42 with the smallest 5.


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PostPosted: Sun Aug 15, 2010 8:29 am 
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Steve Kish wrote:

I've used 11-30 (8-speed) with 20/32/42 rings but only used the 20 with the largest 5 rings and the 42 with the smallest 5.


which is the way to do it to keep proper chain aligment


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PostPosted: Sun Aug 15, 2010 11:04 am 
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FluffyChicken wrote:
with the realisation you either cannot use large-large or your chain will snap or get stuck there.
Or you cannot use small-small else the chain is floppy and skips around.


The only problem is it leaves no margin for error. What if it's dark and/or you're tired and you forget which chainring your in. I've done that plenty of times and ended up in the large-large gear. If you have a replacable hanger you could snap that before the chain snaps.


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PostPosted: Sun Aug 15, 2010 12:04 pm 
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Another issue is with modern cassette ratio's and suspension designs, for which some seem not to consider the fact that mech cage lengths and operation with a growing chain line have not developed, rear mechs are still designed with fixed parameters in mind, suspension frames are not.

We did get mega range when large capacity sprockets appeared on cassettes, manufacturers clearly realised there that current cage length was an issue that a larger Jockey wheel could address.

But none of this seems to stop idiots like Commencal adding a Medium cage Sram to a bike with a gearing completely unsuitable, leaving large large and small small both unuseable while stopping the bike from attaining full travel from the third large sprocket upward when in the big ring.

Gear ratios and cage lengths are there for a reason, safe operation in any gear is what should be addressed with anything else just opinion. The fact is that stating you should not be in big and big is with regard to chain wear a fine opinion, but not actual operation, it is used by many as a bail out gear and by having the correct gear ratio/capacity it is safe to go in and out of it. If you cannot then in technical terms it is wrong spec.

Quite simply, if a customer went into the big ring from middle, while using the rear 34 low, if he lost control of the bike and crashed due to his rear mech hanger or chain bending or snapping the retailer would have a headache.

Try explaining to someone riding a full sus that his chain snapped because he should not have been in 44-28 when hitting a large bump?

Legally any bike that cannot safely operate in and out of all the gear ratios is not fit for purpose and probably should not have an EN sticker on it.

The second line in the picture Andy B posted states "must have" for a reason.


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PostPosted: Sun Aug 15, 2010 12:24 pm 
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JamesM wrote:
FluffyChicken wrote:
with the realisation you either cannot use large-large or your chain will snap or get stuck there.
Or you cannot use small-small else the chain is floppy and skips around.


The only problem is it leaves no margin for error. What if it's dark and/or you're tired and you forget which chainring your in. I've done that plenty of times and ended up in the large-large gear. If you have a replacable hanger you could snap that before the chain snaps.


hence what I typed:?

--
Oh and as pointed out just above, capacity is not just length, that's why we now have an extra tooth on our modern mechs jockey wheels

.


Last edited by FluffyChicken on Sun Aug 15, 2010 12:28 pm, edited 1 time in total.

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