Hey guys,
Sorry for my period of inactivity on this forum. I have now finally gotten my first road bike and love it to bits. But could I get Shimano STI shifters and use them with a different groupset? For example, a tiagra STI lever wth the paddle behind the brake lever on a Shimano 2300 groupset? This has made me pretty curious!

Thanks!

As far as I know all the Shimano road bike brifters work on all the road bike groupsets going back quite a long way. I have a 105 front derailleur pulled by a 4600 brifter, and a 4300 8-speed) front derailleur attached to a 4500 9-speed brifter ....

Do it. Enjoy it.

10 speed tiagra 4700 wont work as it has a different pull than previous tiagra STIs. Same with the new sora r3000.

With that said, if you get STI shifters where the cables exit the side of the shifter in the middle of the bike(vs hidden under tape), you should be good.
This means older ultegra or 105 will work too. Keep it to 9 speed and there will not be a problem at all.

You will of course need a new cassette to match the # if cogs to the shifter speed.

Also- if you want to consider Microshift brand shifters, they make excellent 9sp shifters for the money. I have some 7sp shifters made by them and the 9sp is the same quality and functionality- really solid and good price.

So I will also need to buy a cassette? Why, if I get the same shifter speed?

Thanks

Rear derailleurs don't care about how many gears you have in back. They move however far the cable is pulled. If your shifter pulls the derailleur the width of space to the next gear, you get a smooth shift. if not ....

If you have say, a Tiagra 4600 (10-speed, with the cable exiting the side of the upper shifter body, so it should work) and a nine-speed cluster you get a dead click. You start inthe lowest gear (largest cog) and drop down the cassette (up in gerars) as you accelerate. You hit the top (smallest) cog----but you try to shift again because you lost count. The shifter pulls but because you have limited it with the high limit screw, it goes nowhere.

Then the road tilts up a little and you hit the rear shifter once to drop down one gear ... and nothing happens, because it is the "ghost" gear, the tenth gear which isn't there. So you have to shift it twice. That's about as bad as it gets---nio mechanical harm done that I have ever heard.

(I have Claris shifters (8-speed) pulling an MTB derailleur across a 7-speed cluster----That has problems because of gear spacing differences between 7 and 8 .... but it still shifts pretty well, though it does need that double shift to get things moving at either end ... which can be annoying until one grows used to it. Having to constantly do "shifts-and-a-half" is much more of a pain, but old 7-speed RSX shifters are nearly impossible to find.)

Warning: My knowledge is limited and you would do well to get more opinions than mine and discard mine, like throwing out the lowest score in Olympic judging. Enjoy the performance, complain abut its flaws, reward the better performances.

You have 2300, right? Thats 8 speed. So to get 8 speed with 2 paddles(the style you say you want), you would need very old tech- like 20+ years from the mid90s.

As for the conflicting advice being given, the other poster is mistaken due to changws in recent technology. It used to be true that derailleurs dont care what speed shifters you use. That is no longer the case with current new derailleurs. A new 5800 105 rear derailleur, for example, doesnt work with 9speed sora 3500 STI shifters.
9 speed Sora 3500 isnt even compatible with 9 speed Sora R3000.

This is due to how the shift cables are routed- the derailleurs used now matter.

As far as I know this guy is correct. First-gen 10-speed Tiagra (4600) is included.