Changing Hybrid to Tourer

As Robert says 135 OLN is the MTB rear axle spacing standard and there are a whole host of 8,9,10 speed ‘MTB’ hubs available that either a 8, 9 or 10 speed cassette will fit onto. The cable pull for “Road” and “MTB” Rear Mechs are the same, so you can use either type with STI Road Shifters. One thing to consider is, for touring and hauling a load up hills, you may want lower gearing i.e a 11-32 T cassette, which a Road Rear Mech may or not be able to handle, especially with a Triple Crankset at the front.

Tiagra is now 10 speed but looking at what I assume your 9 speed Tiagra Rear Mech is (RD-M4500), it says maximum rear sprocket 27T. So to get low gearing for touring where it is hilly I would personally recommend you use a MTB Rear Mech (which to reiterate will work with Road STI’s) and an 11-32T cassette.

The cable pull for the Front Mech is different between ‘Road’ and ‘MTB’ so to work with STI Road Shifters you will need a ‘Road Front Mech’.

This now opens a can of worms! ‘Road’ is designed for a 45 mm chain line. ‘MTB’ is designed for a 50 mm chain line. So your Alivio Crankset outer chain ring is 5mm further out than where a Road Triple outer would be. Hence with a ‘MTB Crankset’ (like your Alivio) fitted, a Road Front Mech might not be adjustable far enough out to prevent chain rub when on the large front chain ring or even cleanly shift the chain to it. A solution if the Front Mech isn’t adjustable far enough out would be a shorter axle bottom bracket to move your Alivio crankset inboard (onto a 47.5 mm or 45 mm chain line) , but then there is the potential problem of clearance between the inner chain ring and the frame (chain stay).

That said I ride a Touring bike with STI shifters (old 8 speed Sora) with an old FD-M2303 Road Front Mech that works perfectly with a 50 mm chain line Triple Crankset, (like your Alivio one). I’m sure someone on here will be able to confirm if a newer / “higher up the ladder” Road Front Mech works with a MTB Crankset.

Why not use bar end shifters? Not sure if you could get them indexed to 7 speed, but they should work just fine as friction shifters. Then you don't need to shell out for sti brake levers (brifters sounds so wrong), all you'll need are basic road brake levers (cane creek or tektro make them) that way you only need to invest in gear on the bars and keep the drive train.

Also bear in mind bar diameters may differ between flats and drops. If they are different you'll need a new stem to hold the bars.

130 OLN is typical for 8 - 11 speed road bikes, 135 OLN is an MTB standard. There's no end of choice of 8,9,10 speed 135mm hubs.

My concern would be the extra reach of drop bars. Typically, flat bar bikes have longer top tubes than drop bar bikes. Putting a drop bar on it may stretch your riding position too much unless the current bike is a sit-up-and-beg type.