So i’m umming and ahhing over whether to go single or double ring on new build. Thinking of starting single, see if its fine, and then changing to double if its not. with this in mind I was just gonna get a med cage mech, to allow options in later life etc.

My question, if I stick with single ring, what will be the negatives of having medium of short cage rear mech (or a longer cage in general). Just greater exposure to rick strikes etc or is there more? Obviously the cage will spend more of its time in the forward position as there won’t be as much slack as the design intends.

Feel free to discuss the question in any way that appeals to you

Ta muchly, Unk.

have you checked out the capacity of the ones you are interested in on the shimano site (assuming you are going shimano)? You might find you actually get away with the one you want.

shorter one will be fractionally less at risk of damage and crisper but the best way to avoid damage is shift to a ratio that tucks it out of the way better when you get to anything rocky and pointing downwards.

I always want to get short cage rear mechs as I only ever run single rings, but they never seem to be in stock so always get medium cage.
downsides are aesthetic (short looks better IMO) and weight (v. small) and the fact that you have less chain in contact with the chainring because of the angles created by the longer cage, which therefore makes it slightly more susceptible to dropping the chain. but if you’re running a single ring you should really have some kind of chain keeping-on device.

As an aside, what about using a road mech?