Rear Mech cage length help.

dirkpitt74

I've got a new frame that I'm going to build up over the winter - 2013 Nukeproof Mega TR - so far have acquired a few nice bits for it.

Looking into getting a new 2x10 SLX group set, but not sure about rear mech cage length.
Have read a couple of articles and I'm now confused.
I'm planning on running 2x10 with 28/36 front and 11-36 rear.
One article suggests medium cage where the other says long.

Found this formula for calculating capacity:

T = (big front + big rear) - (small front + small rear)

With the above combo it works out at 33 teeth.

Shimano spec for the mech is:
Medium Cage 35T
Long Cage 43T

So based on the above I could use a medium cage.
But if I changed any of the ratios though (i.e. went with a 40T expander on the back) I'd need to go long cage.
Do I need to take into account chain growth as it'll be on a full susser?

No price difference between the 2, just want to order the right one.

Confused!

cooldad

Formula should be big front - small front plus big rear - small rear.

cooldad

Which is the same I suppose.

dirkpitt74

Yep - gives same answer lol

The Rookie

All correct, medium cage suites, if you had a frame with big chain growth you may need a longer cage but the cage has some 'headroom' and the TR isn't too bad for growth. An expander is probably out though - you could try it (carefully) and see.

dirkpitt74

DOH!!!
Scratch that - front is 26/38 not 28/36 - so puts it over the 35T capacity (37T).
So will be running the long cage - gives me a bit more room if I want to change ratios.

Cheers chaps!

jimothy78

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19758876#p19758876]DirkPitt74[/url] wrote:

So based on the above I could use a medium cage.
But if I changed any of the ratios though (i.e. went with a 40T expander on the back) I'd need to go long cage.

Yes, but the range expander is only really meant to compensate for the lack of a granny ring when switching to 1x - I've never heard of anyone using one together with a 2x setup. And switching to only one chainring, you'd still only need a medium cage mech.

jimothy78

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19758932#p19758932]DirkPitt74[/url] wrote:

DOH!!!
Scratch that - front is 26/38 not 28/36 - so puts it over the 35T capacity (37T).
So will be running the long cage - gives me a bit more room if I want to change ratios.

Cheers chaps!

I was about to ask about that - thought it was very odd to retain two rings, but then have such close sizes that the resulting range wouldn't have been much different from a 1x setup.

The Rookie

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19758945#p19758945]jimothy78[/url] wrote:

Yes, but the range expander is only really meant to compensate for the lack of a granny ring when switching to 1x - I've never heard of anyone using one together with a 2x setup. And switching to only one chainring, you'd still only need a medium cage mech.

I know someone using an expander (40T, not 42T, don't want to be silly) on a 3x setup, watching him climb a hill in 22/40 is a giggle, well for a while but not a giggle for as long as it takes him to get up said hill!

A bit frustrating when you just climbed the same hill in 32/34!

dirkpitt74

Perhaps I need to re-think my gearing then.

Wanted to stick with 2x10 as I didn't think 1x10 would suit.

My current 2x10 36/24 front and 11-36 spins out on the flat/downs hence wanting to go to a 38/26 front.
On the hills the 24 - 36 hardly gets used as it's a bit too spinny.

But now thinking about it the ratios are fairly close so perhaps going for 11-34 on the back is a better bet?

The Rookie

I don't see it an issue spinning out on the downs, if you have the right cadence a 32/11 is doing about 26-27mph, off road I see little point in trying to pedal going much faster! 34/11 would be doing 30mph.

I suspect this is you thinking you are spinning out rather than actually teaching yourself you can spin your legs at 120rpm.

However if a 1x is out then something like a 26or28 inner and a 38 or 40 outer should do the trick.