I decided to build a DS bike. The gearing is 24 speed with 11/34 free wheel on back.
Would you go with long or med. cage rear derailuer? Is there less chain slap with med. cage?
Thanks to all that respond........

Of course there is a less chain slap/play with the shorter cage, but probably not enough to matter much. That said go with the short cage if it fits your gearing and you KNOW you will be happy with it. If you think you may want to increase your granny cog later then go with the long cage.

All things being equal, the long cage will wrap more chain, and therefore have less slap. More importantly, however, is the calculated wrap capacity requirement of your drivetrain, and the capacities of the two derailers. For your drive train, (34-11) + (44-22) =45. If both derailers can wrap 45 teeth worth of chain(listed on the derailer specs) I would choose the smaller(and therefore lighter) cage.

What does DS stand for?

Oh . . . no . . . it's too cheap . . . must . . . resist....

Dual Slalom? Damn Slow? Dual Sport? Dirt Slinger? Definitely Sucks?

Uh, That would be Dual Suspension.......

Ahhhhh . . . forgot about that. Used to seeing it as FS.

In answer to you question (well, my opinion really) . . . I would go medium cage. Less banging around and a little less vulnerable.

I'd go for medium cage too.

Ditto

Ditto

^^ Hey, you are still alive.

I am yes...I hang out in foo quite a bit ...

Uh, well that's good because a Dual Slalom bike with that drivetrain would be ridiculous

Front Suspension?

Hey dude.

hey......I don't recognize the handle, but that doesn't mean much...hahaha

^^ We changed it because the old one had become synonymous with 'weaksauce' and 'pushover.' He needed something that sounded more 'abominable.'

Thanks for all the responses. Looks like I will go medium cage. Thanks........

Since you say you have a "24 speed" I take that to mean you have a triple crank with an eight speed cassette. You need a long cage derailleur, a medium cage doesn't have enough chain wrap capacity for a triple with a mtb cassette. Medium cage mtb derailleurs are intended for mtb drivetrains with only two chainrings. The long cage models are for triples.

^Agreed! Long cage for triple chainring up front!

I semi-disagree. As long as you don't seriously cross-chain (and really, how many people use the big ring on an MTB unless they're in an almost-spun-out situation anyway?), you should do fine with a medium cage.

Example: a medium cage derailleur with a capacity of 38. Front difference of a 44-32-22 is 22; rear difference of a 12-32 (typical 8-speed) is 20. Sum is 42 - - not far enough off 38 (IMO) to where you can't easily fudge it if you don't do silly things.

I disagree with your semi-disagreement. Number one rule of chain sizing is make sure the chain is long enough to safely shift to the largest cog/largest chainring. With that in mind, with a triple crank and medium cage derailleur, when in the smallest chainring there will be a few gear combinations (the smallest few cogs on the cassette) where the chain is too slack to function correctly. Should you severely cross chain? No, of course not; not in the big ring, not in the small ring. Do people do these "silly things?" Based on my experience working in my bike shop: yes, very often. The simple, straightforward answer to the OP's question is to get a long cage derailleur. His type of drivetrain is what they are designed for. A medium cage is not.

I just checked- Shimano medium cage has a 33T capacity, Sram medium cage has a 37T capacity. OP- DO NOT GET A MEDIUM CAGE! You need a long cage derailer.

i disagree with your disagreement of dminor's semi-disagreement.
he is here asking the question (and building up his own bike from the sound of it), so he is obviously not one of those morans* that runs big cog + big ring. he has been warned that he won't be able to run that gear, so i think he can run the medium cage if he wants to. he's a big boy. if the "no big-big for less chain slap" compromise is one he is willing to make, let him. it seems like less chain slap is what he is after, so he is probably willing to give up that moranic gear combination to get it.
the real question is: what if he wants to go to a 34t rear cassette? then he would have to change to a long cage. that by itself would make me go with a long cage.

First, a long and medium cage mtb derailleur both have the same largest cog compatibility. The only difference is cage length, which affects chain wrap capacity, not largest cog compatibility.

Second, it's irresponsible to advise someone to use a chain that's too short to safely shift to the largest cog/largest chainring combination. It is indeed moronic to run a chain that's too short to do this. One brain lapse and you'll likely snap your deraiiler, your hanger, your chain, maybe damage your rear wheel, and maybe even your frame. Risking this for what reason? The difference between using a medium and long cage deraiileur?

Bottom line: if you have a mountain bike with a triple crank, use a long cage deraiileur. That's why they make them. And make damned sure your chain is long enough to safely cover the largest cog/largest chainring, no matter what.

I thought this thread was over after the first few answers. So I ordered a medium cage. What is a medium cage used for if not for a mountain bike with 3 chain rings. If I get a smaller free hub will the medium cage work? Lessons learned I guess......

^^ Always take everything on interwebs forums with the caveat that what we say is usually JUST ONE PERSON'S OPINION. And those opinions often differ. I qualify what I say quite often but sometimes I don't; but, really, that should be a given.

You really don't need to do anything drastic (IN MY OPINION). I personally would lose the big ring, put a nice bash guard on and maybe go up to a 36 middle ring anyway. Since you're building this, take the opportunity to customize some of your build to better suit the way you're going to ride it.

More info on chain wrap on the late Sheldon Brown's web site which you may find some comfort in:

https://www.sheldonbrown.com/harris/derailers-rear.html

See his note about capacity.