Looking to upgrade the drivetrain on my Cannondale Ironman 600 (mix of 105 and Tiagra components) to a complete 105 or Ultegra set. Would this be a direct swap or are there other considerations I should take into account? I'm wanting a lighter and more reliable drivetrain for longer distances. Total noob so any advice is appreciated.

I doubt you will encounter much problems. Also there is no reason, other than wear and ajdustment that your old drivetrain cannot function as good as the 105 or ultegra (save for the possible newest 6700 group - but that will entail changing more than just the drivetrain bits.

Chain, cassette, bottom bracket and crankset are likely to be no problem. Same with the derailleurs.

According to bikepedia, other than crank and front derailleur, you're all 105. I don't think changing that little will improve reliability much, if any, at least in any way that couldn't be achieved by regular maintenance and proper adjustment.

One thing to note: current 105 is 10sp, while yours is 9sp.

As barturtle noted, you won't see much in the way of increased performance or decreased weight. If you go Ultegra, you are basically starting over as you'll be going 10 speed. I would think a new bike would be a better deal at that point.

Yes, I agree. I feel my bike shifts better with Ultegra. It's fun to do, so go ahead and play with it.

Should be a straighforward swap, but unless something on your bike is broken or completely worn out, it is a waste of money.

For what it's worth I replaced a left 105 shifter with a left Ultegra shifter (5510 to 6510) on one bike and I could not tell the difference. I got the Ultegra shifter for $40 so I figured what the heck. The bike is a mongrel of parts and at the time the right shifter was a Sora. Now I'm going to put older Campy on it with the goal of at least having the shifters match. ;-)

Thanks for all the replies! After taking all of your feedback into consideration and talking to a few friends I've decided to keep the bike stock and upgrade only as needed. As someone suggested, it may be more worthwhile to save up for one of the many newer, lighter models.

If you want to feel an upgrade, shell out on nicer wheels.

And pay attention to your gear ratios with an eye to improving them when it's time to replace your chain and cassette.

Ok, I need to replace the cassette and chain on my road bike, as they are worn.

My bike is a 2007 specialized Roubaix Elite Triple - 105 derailleurs and cassette (10 speed)

the cassette is 12-27, and the chainrings are 50-39-30

not sure if it matters, but about 7 or 8 months ago, the RD god sucked into the spokes (bent hanger?) and destroyed. I replaced it with a new 2009 105 RD.

Anyway, I understand that I _can_ replace the chain and cassette with Ultegra instead of 105, but what I want to know is..., is there any particular reason to do so. The price difference is minimal, so if there were any reason to expect better shifting, I would do it.

on the other hand, i guess it's possible that the 105 RD and FD will work better with the 105 chain...

So, which is it:

a) ultegra cassette and chain will shift better than 105 cassette and chain

b) 105 cassette and chain will shift better than ultegra cassette and chain

c) no perceptible difference

also, other than counting the links, how do i know what size chain to get?

c) no perceptable difference. The Ultegra cassette will be slightly lighter but otherwise they will perform the same.

New chains all come the same length (114 or 116 links) and you shorten them to fit your particular bike and gearing. Sheldon Brown has an article describing the best way to set the chain length: https://www.sheldonbrown.com/derailer...ent.html#chain Scroll down to "Chain Length" and follow his directions. You will need a decent chain tool.

Ride it until it wears out and replace the parts as necessary. There is no upgrade in performance when going to 105 or Ultegra. They might last a little longer.
Weight should never be a consideration unless you are getting paid to race and you are 5% body fat and capable of generating 450 watts for an hour.