I want to upgrade from shimano 2300 2x8 to 105's. I don't care if it's 2x9 or 2x10. I live in the Low Country and I never use the gears I have now. If I want to do any climbing I have to ride back and forth over the interstate bridge. So given that, the only real reason for the upgrade is I'm not fond of the thumb trigger. I don't spend every second in the drops but when I do I'd like to be able to shift without reaching back over the bars. The shifters I have work well and shift nice and crisp, it's just the thumb button issue.

I want to buy the parts here and there as I feel like spending money. Obviously I'll need new shifters, cassette and chain. Will this work without new derailleurs? I'd do it without the cassette if I could. What parts are absolute and what can be left alone?

I'm only asking because I'd like to put the new set to use even if I'm mixing group parts up until I get the whole set put together.

105 (current 5800) is 11 speed, and your rear wheel won't be compatible with the cassette fit, even if you looked at older 5700, there aren't any parts which are compatible between a 2300 and 105(5700 or 5800) versions (9 speed 5500 is 3 generations ago, and no longer supported), even the brakes would need changing (technically although they may still work with a different feel), as the pull has changed

Well crap. Didn't realize I'd have to spring for new wheels too. Looks like I have more work and money involved than I thought.

Thanks for the help.

Amigo, do you have any strong overriding love for the bike you have now?

Because as pointed out, "upgrading" will probably end up costing more than the $$ value of the frameset. The gruppo alone is $500 or so then you need wheels do to the dishing requirements of 105 11-speed.

No, I do not. I enjoy it, but that's as far as it goes. It's an entry level Secteur, it rides good, it fits me and what I do. Now given the info here, I'll be riding it for a while longer.

I was really just being hopeful about upgrading the components. I'll keep it as is and get a new bike in a year or so.

Keep in mind that there are great deals to be had on upper-end used bikes, and that will become more true as we get into winter.

You have good choices other than 105. Tiagra 10 speed, Sora 9 speed, and Claris 8 speed shifters have all done away with the thumb levers. Claris shifters would be a straight swap, no need to change cassette, chain, or anything else. The latest versions of 105, both 10 and 11 speed feature revised brake pull ratios, so braking power would be compromised.

Perfect. Like I said, I don't necessarily need any additional speeds, I just want to get rid of the thumb levers. The Claris is exactly what I need. I'm assuming I'd still need to do a wheel swap with a 10 speed Tiagra? I can't get the whole "move up the product line" out of my head though. Silly.

Shimano 8, 9, and 10 speed cassettes all fit your wheels. It is only if you move to 11 speed that your cassette body would have to be changed if it is at all possible

This is true.

I use a Sectour in my trainer, and had to swap out the original shifters (one went FUBAR big time)...Found a set of used Ultegra 3x9 shifters on eBay and swapped in a 9spd cassette. Rear shifting is smooth as butter, but the FD must have a different pull ratio as neither I nor the LBS can get it to work smoothly, so a FD replacement may be in order. If you go this route, look for grifters with the shift cables exiting the side of the bodies (as opposed to running under the bar tape), I think the brake pull ratio should be better for your brakes.