I'm new here, and I want to convert my triple to a compact double.
I have new 105 black (5700) components in a triple.
I want to use a SRAM Rival compact crank and a new 105 short cage rear derailleur. I'd like to use my 105 triple shifters with the double set-up.
Can this be done? If so, how?

Thanks,

Peter

Yes. Set up the front derailleur limit screws. Now the front shifter will only be able to use two of the three positions. You can use inner/middle or middle/outer positions and the FD effectivel locks out one of the end positions.

Using inner/middle will lock out the outer position completely. However, you may be able to damage the shifter if you accidentally try to upshift into the outer position because the FD won't allow it to move, but you can wear the mechanism by trying to force it. Someone said a while back though that this problem was mainly seen on Tiagras.

Using middle/outer won't have the above problem. However, it will still allow you to shift into the inner position, but the FD won't move in any further, so the line will just be really slack.

Might not have to do anything. Shimano uses the exact same part number for 9-speed double and triple shifters.

I've owned a triple crankset equipped tandem and a double crankset equipped road bike that used the same Ultegra 9-speed STI shifters. They actually had 4 shift positions. On the triple I had 1 shift position for the granny, 2 for the middle ring and 1 for the big ring. The double had 2 shift positions for each chainring. I also had Flight Deck computers on both bikes and both computers always indicated the correct chainring so I know that I had them set up the way that Shimano envisioned.

Now the question is: "Will it work the same way with an 8-speed or a 10-speed cassette?" If it was my bike, and I already owned triple crankset shifters, I'd sure give it a try before spending money on new ones. If I was buying new shifters, however, I'd hold out for the ones that Shimano recommends.

I have done that. I now have a triple 105 shifter with a double crank.

After replacing my triple crank with a double and using the same FD, I just began tightening/loosening the H/L limit screws of the FD. Observing how the shifting reacted to each turn and compensated accordingly, I adjusted till it was perfect.

The final outcome was I was able to lockout the inner small ring and the shifter too. The shifter operates as if it was an actual double shifter. Big/small ring.

I dont recall how many turns, etc of the high and low limit screws, but to answer your question - yes it had been done.

Adjusting limit screws does not take trial-and-error.

Cable should frst be detached. Chain should be on the inner chainring and inner (largest) cog. Adjust L limit screw so that inner plate of FD gets as close to the forward-moving chain as possible without rubbing.

With shifter in either the inner or middle position (depending on which you want to use with the inner chainring), attach FD cable taught (make sure shifter is in the actual chainring position, not the trim position). Shift to outer chainring (may or may not want it in the trim poistion) and outer (smallest) cog. Adjust H limit screw so that outer plate of FD gets as close to the forward-moving chain as possible without rubbing.

This is the most concise-yet-thorough description of the process that i've ever read. Well done, jiveturkey.
-rob