alathIN

I have a 10sp Tri bike, and have an occasional hilly event.
I'm kind of stuck with my chain ring set, so the best way I have to deal with hill is change the cassette.
My short cage RD doesn't like the 32t cassette.
I have a medium cage RD. Can I just put the medium cage on and leave it?
Or is there some reason to put the short cage back when I'm back from Hilly Land?

HillRider

Some will claim a longer cage rear derailleur shifts slightly slower but I've never seen the effect. It also adds a few grams which some rider consider a crippling penalty. And of course, there is the derision you will suffer from your fellow racers as they point to and laugh at your "tourist" gearing.

Andrew R Stewart 

Seems to me that you'll be a faster finisher is you control how much effort you use up during the ride portion of a tri. So gear the bike to whatever that takes.


Sometimes a mid cage rear der will allow a 32T cog, sometimes not. But if you never cross chain (big-big) and if the upper pulley clears the large cog when in the smaller ring and you never cross chain in big/big you'll be fine (If you never use the big=big). Andy.

dsbrantjr

You will of course need to have sufficient chain length to go into big-big even if you never plan to use it, because you WILL forget eventually (

Bike tinker man

Assuming the Mid cage RD is designed for 10.sp there should be no problem no need to keep on changing back, I doubt you will notice the difference, as mentioned above you will need to make sure the chain is long enough, also the mid cage RD may have a different swing, so you will need to make sure the RD cable is OK, also remember to check & re-adjust the B screw if needed.

Slash5

You say "My short cage RD doesn't like the 32t cassette."
Depends on what you are trying to accomplish. A medium cage derailleur has more chain take up but won't necessarily handle a larger rear cog. You need to check the specs.
If the derailleur doesn't shift well to a 32 T cog then you may have to go to a different model of derailleur rather than just a longer cage.

bradtx

@alathIN, I can only compare a pair of Ultegra RDs on a pair of Cannondales I have. One is a short cage for a double and the other is a long cage for a triple...there is no noticeable difference in the shift quality.

You may want, or need to use a RD from a mountain bike group to accommodate the 32T bottom cog. If so, I can report that my XT RD shifts quite well also.

Point is that you don't need to switch RDs for smaller capacity cassettes.

Brad

Facanh

What short cage and what medium cage derailleur you have exactly? A longer cage derailleur can take up more chain slack (like if you have a triple) but it does not necessary mean it can handle a larger cog in the rear better.

For example, I have a super short cage ZEE mountain bike rear derailleur, and it can handle a 36T no problem, but since it's capacity is low because it's a short cage you can pretty much only use it in a 1x10 setup.

But to answer your question, using a long cage derailleur even when you don't need one is perfectly fine. You won't notice a difference. If you compare the exact same model a short cage might be a few grams lighter, but that's about it.

alathIN

SRAM rival short cage, vs. rival wifli/mid cage. SRAM says the wifli will work with my 1050 32t.

I can grind up a hill at slow mashing cadence if necessary, but probably will have a happier run if I can avoid that.

Thanks for the info.

jsdavis

The mid cage will have a larger minimum big gear compared to the short cage. The short cage probably spec'd to works with 11-23, 11-25, 11-28; and 11-28 and 11-32 for the mid cage. The mid cage should still shift the three smaller range cassettes, but you might be unable to adjust the B screw enough to get the upper pulley as close compared to the short cage. Shifting might be slower or less smooth as a result.

Facanh

Oh yeah crap I forgot about the single pivot design... Although, on most sites I don't see anything in the specs like "minimum biggest cog" for the Wifli medium cage. CRC is the only site that lists this in the specs:

"Compatiblity: Cassettes from 11-26 to 11-32"

With MTB RDs SRAM and Shimano (only Shadow of course) always lists this spec but for this particular RD other than CRC I did not see anything.