Epicus07

I want to run a 13/29 with a 39/53 crank on a 10 speed campy centaur drive. The rear derailleur is a short cage.

Will this work perfectly or will i need to buy a new RD ?

thanks

HillRider

It will work but not perfectly. The short cage won't "wrap" enough chain to allow use of the full range of gearing.

Campy claims a total tooth capacity of 27 teeth for their short cage rear derailleurs and your combination has 30T. If you size your chain to allow big-big, (which you must do to protect the components), you probably won't be able to use the 13 or 14T cog with the 39T chainring. That's not a real sacrifice but it's why Campy recommends their medium cage rd's with this particular gearing choice.

DaveSSS 

This combination will work with some bikes and not work with others. If you have the perfect chainstay length, up to 3T of wrap capacity can be had. There may also be problems with the upper jockey pulley clearing the 29T cog, in the little ring. That varies with the derailleur hanger length.

To figure out the perfect chainstay length, use the rigorous chain length formula from the Park Tool website. When the result is a length that a nearly perfect whole inch length, like 53, 54 or 55 inches, then you have the maximum wrap capacity. If the suggest length is something like 53.25, then you must use 54 inches, just to gain 1T of wrap.

Adding 1 inch of chain increase the wrap capacity by 4 teeth, but as already mentioned, that may cause the chain to hang loose in several of the smaller cogs, when you're in the little ring.