Difference between Long and short Cage for Rear Derailleur

[awesme]

Hi guys

 

Looking at the following 2 detailers atm

 

Shimano XT M781 10 Speed Rear Mech

http://www.chainreactioncycles.com/Models.aspx?ModelID=86801

 

Shimano XT M786 Shadow+ 10 Speed Rear Mech

http://www.chainreactioncycles.com/Models.aspx?ModelID=83162

 

Other than I get the feeling the M786 is much better...

 

Whats the value of the Long cage of the M781

 

G

[DR ◣◢]

Also would like to know. Sitting with a brand new XTR Shadow 9spd with carbon cage on my desk but it's a long cage.

 

I know it will work on my bike but a short cage would look nicer

[Seadog]

Short for DH, Medium for 2X10 and Long for 3x10

[awesme]

easy enough/simple enough.

 

Thanks

 

G

 

Short for DH, Medium for 2X10 and Long for 3x10

[braailegend]

Short cage looks cooler. But most freeride/jumpbikes ride shortcage. I also have one but haven't noticed any difference yet to my longcage. Maybe if you run 3 blade it necessitate a more chain thus longer cage to keep tention

[Iwan Kemp]

Short for DH, Medium for 2X10 and Long for 3x10

 

Copy and paste...

 

Has to do with ratios. In other words what size chainring and cassette combo you are using. Yes, DH does use short cage, but most of the time those are running road cassettes with a 25 or 27T "Granny" plus the shorter cage ensures less chance of rock damage when bombing down the mountain.

[awesme]

Hi Crow,

 

doing a 3x10

front (42/32/24)

rear (11-36)

 

So guessing a long cage is needed.

 

G

 

 

 

Copy and paste...

 

Has to do with ratios. In other words what size chainring and cassette combo you are using. Yes, DH does use short cage, but most of the time those are running road cassettes with a 25 or 27T "Granny" plus the shorter cage ensures less chance of rock damage when bombing down the mountain.

[Iwan Kemp]

When I was still riding 3x9 I always used Med cage and I was running 44 big blade with a 34 Granny. You should be fine with a Med cage. 10spd, 9spd, 8 spd is irrelevant as long as the top and bottom ratios are comparable.

 

Cage lenght is there to pick up extra slack from chain.

[TNT1]

Hi Crow,

 

doing a 3x10

front (42/32/24)

rear (11-36)

 

So guessing a long cage is needed.

 

G

 

You guess correctly.

 

You only need a long cage for a triple clanger up front.

[LazyTrailRider]

the shorter cage ensures less chance of rock damage when bombing down the mountain.

That, and it reduces chain slap because there's less movement.

[awesme]

Ok, so now one guy is saying it should be ok, one is saying I need a long cage.

 

Lets make this more interesting, I'm planning on running a Chain guide.

 

The short cage looks better, but if I need the long one I don't have a problem.

 

G

[splat]

chainwrap capacity = big ring - small ring + big cog - small cog

 

Manufacturer stated derailleur capacities are as follows:

Shimano long = 43T; medium = 35T

SRAM long = 43T; medium = 37T; short = 30T

 

I have 38-34 rings and an 11-36 cassette

so, 38-24+36-11 = 39t

 

So I got a long cage rear derailleur.

 

There is another thread here: https://community.bikehub.co.za/topic/120486-rear-derailleur-length/page__hl__cage

Edited October 17, 2012 by splat

[Johan Bornman]

Every derailer has a range. This range is measured in teeth, as in sprocket teeth.

 

If you exceed the range (expressed as a number), your derailer will stretch too far forward in big-big and possibly rip off and go into the spokes. Conversely, if you make the chain longer to cope with that problem, it will not create chain tension in small-small, leaving the chain hanging.

 

The range is not widely known but available on the brochure and on the websites.

 

How to calculate the range you need:

 

1) Take the tooth value of your largest chainring (say 44) and deduct the tooth value of the smallest chainring (say 22). The anser in this case is 22. Keep that in your memory.

2) Take the tooth value of your largest sprocket (say 32) and deduct the tooth value of your smallest sprocket (say 12). The answer is 20.

3) Now add 22 and 20 (for this example only) and get 44.

 

Your jockey for the above example should have a range of at least 44. If it is say, 32, it will create the scenario I started off with.

 

Don't create a Frankenbike with wrong jockeys and large tooth ranges. It doesn't work. Buy the right jockey first time.

 

Edit: Splat beat me to it. Use his real-life examples to create your own answers.

Edited October 17, 2012 by Johan Bornman

[DR ◣◢]

So what you are saying is running a long cage on a 1x9 using at 32t to 34t chainring and a 11-34t cassette is not the right thing to do?

[awesme]

Hi Johan

 

Now remember you mentioning this during the course.

 

So my numbers: (42-24) + (36-11) = 18+25=43

 

Rear Derailleur

I see on CRC they mention something about "Total Capacity teeth" listed as 14, I'm guessing this is a teeth capacity for the rear cassette, guess they're showing the medium cage length, being 14 teeth, can't seem to select a long cage to see the capacity there

http://www.chainreactioncycles.com/Models.aspx?ModelID=83162

 

Front Derailleur

Teeth Capacity = 18 teeth, now I think If I understand things correctly then I have a problem, I need 25.

http://www.chainreactioncycles.com/Models.aspx?ModelID=83625

 

How am I doing.

 

G

 

Every derailer has a range. This range is measured in teeth, as in sprocket teeth.

 

If you exceed the range (expressed as a number), your derailer will stretch too far forward in big-big and possibly rip off and go into the spokes. Conversely, if you make the chain longer to cope with that problem, it will not create chain tension in small-small, leaving the chain hanging.

 

The range is not widely known but available on the brochure and on the websites.

 

How to calculate the range you need:

 

1) Take the tooth value of your largest chainring (say 44) and deduct the tooth value of the smallest chainring (say 22). The anser in this case is 22. Keep that in your memory.

2) Take the tooth value of your largest sprocket (say 32) and deduct the tooth value of your smallest sprocket (say 12). The answer is 20.

3) Now add 22 and 20 (for this example only) and get 44.

 

Your jockey for the above example should have a range of at least 44. If it is say, 32, it will create the scenario I started off with.

 

Don't create a Frankenbike with wrong jockeys and large tooth ranges. It doesn't work. Buy the right jockey first time.

 

Edit: Splat beat me to it. Use his real-life examples to create your own answers.

[TNT1]

So what you are saying is running a long cage on a 1x9 using at 32t to 34t chainring and a 11-34t cassette is not the right thing to do?

Yes.