I have a Shimano Ultegra 50/34 compact crank and have been reasonably happy with it, other than the extra rear cassette shifting I have to do when I switch between the chainrings, as there is a 16 tooth difference between them.

I ran some gear calculations and I think I would prefer a 50/36 set up while keeping my 12-25 rear cassette. My questions are, can I just purchase someone else's 36 chainring as Shimano apparently does not make one, do I need to purchase a matching 50/36 chainring pair from someone else so the ramping and pins work properly and the shifting is optimum, or do I need to purchase a completely new crankset from someone else (FSA/Ritchey etc.) to make this work?

Any feedback, especially from those who have done this would be greatly appreciated. My front derailleur is Shimano Ultegra as is the rear derailleur if that matters. I believe the compact crank I'm currently using is a Shimano 600 series. Thanks...

You can certainly change out the rings to FSA or some other 110BCD set of rings without changing the cranks. I do think you will want both inner and outer rings to be the same brand though.

I have a question.

Why?

There is a difference of 2 teeth. Ain't much of a difference. If you want to move things around, get a standard road crank and a larger cassette, say a 28 or 30 to give the gear inches you want in low gear.

Mainly because I find the 53 not much use at my size (5'6") and age (56). When I've had the 53 I lived mostly in the 19/21/23/25 and rarely used any of the other gears. I also found myself switching chainrings a lot during a ride.With a 50 large ring, I can make use of more of the cassette, especially where there is a single-tooth jump such as the 15/16/17, and I spend most of my ride in the big ring which I prefer.

Part of the decision to consider a 50/36 is to not have a 16 teeth difference along with the associated extra shifting I have to do when going from one chainring to the other, and part of it is to find a way to keep the 50 big ring which allows me to spend most of my ride in the big ring.

Actually, the difference is more than most would think. After shifting between the chainrings, you can shift one cog less to reach the next higher or lower gear ratio. The percentage difference is a lot closer to the standard 53/39, but all ratios are just a bit lower.

The OP's complaint is about the extra cog shifting after a chainring shift. With Campy shifters it's a bit easier, since one push of the thumb button will shift as many cogs smaller, as needed, rather than tap, tap, tapping a Shimano or SRAM shifter. Most shifters will do 3-cogs larger with one sweep of a lever excpet the new DA 7900 that can only shift 2-cogs larger.

A 36 is a big improvement over a 34, better range of cruising gears if you don't need the low end.

You should be able to drop an FSA in there without any problems, assuming your chain isn't too worn.

Most people will have to double shift when going from small to large ring on a compact (or 52/39 or 53/39)

However, if you want to change, the reason to get your chainrings in pairs is because of the ramps and pins. You would probably be OK with anybody's 36, but the ramps/pins are optimized for a 34 inner...

In theory the shifting will be crisper with a matched set... But, I have no experience to prove or disprove this.

[QUOTE=DaveSSS;9446493]Actually, the difference is more than most would think. After shifting between the chainrings, you can shift one cog less to reach the next higher or lower gear ratio. The percentage difference is a lot closer to the standard 53/39, but all ratios are just a bit lower.

The OP's complaint is about the extra cog shifting after a chainring shift. With Campy shifters it's a bit easier, since one push of the thumb button will shift as many cogs smaller, as needed, rather than tap, tap, tapping a Shimano or SRAM shifter. Most shifters will do 3-cogs larger with one sweep of a lever excpet the new DA 7900 that can only shift 2-cogs larger.[/QUOTE]

^^^
What he said...

I have got to learn the lingo...

A 50/36 setup makes perfect sense to me.