I am currently have campy 59/39 10 speed and I am looking to go from a 11-23 to either a 12-25 or 13-26 to help in some climbs. I currently have a standard( short cage Dr,)Will I need to increase my chain lenght?

A bit. I would say one link.

Pierre

I doubt it unless the chain is already close to the limit on either the short side or the long side. Put the new one on and check to see that when the chain is on the small to small combination there should be no slack hanging and the rear derailleur should not be very close to its rearward limit. In the big to big combination the rear derailleur should not be near its forward limit. When in the big to small combination the derailleur should be semi-perpendicular to the ground.

Al

The short cage is perfecty capable of handling a 13-26 and the chain would not need lengthening if the length was properly adjusted in the first place, but unfortunately, rather than do it the correct and simple method, many people resort to shortcuts and guess work methods. The following will work with any derailleur.

Two simple tests will determine if the chain is the correct length. First, it must not hang loose in the little ring, little cog combination. If there is no tension on the chain in the little ring, little cog combination; remove two links (one inch) at a time, until there is. When the ends of the chain are brought together, some movement of the lower pulley should occur, indicating tension is being applied. Two more links (another inch) may need to be removed, beyond the point of absolute minimum tension, to keep the chain from rubbing on itself as it passes under the upper derailleur pulley. If you want to see how much lower pulley movement will occur, without removing the extra inch of chain, shift up four teeth (11 to 15 or 12 to 16). This has the same effect as removing two links. Once this is done, the chain is set to the maximum useable length. Removing additional links will do nothing but reduce the derailleur's capacity.

Second, the chain must be long enough to avoid over-extending the rear derailleur when shifted to the big ring and biggest cog combination. If the chain is set to the maximum length as described, it should always pass this test, unless your setup exceeds the derailleur's stated wrap capacity. If you deliberately exceed the derailleur's capacity and the derailleur is over-extended in the big ring/largest cog combo, then you must either avoid that combo or add another inch and avoid using the little chainring and the smallest 3 or 4 cogs (since the chain will hang loose).