I'm touring on mine Trek 4500 Disc (2011) it's a mountain bike. All parts are from factory/standart.
What parts should I upgraide or to have spares in my repair kit ( what parts are more likely to fail)?
I also bought a Trek 4500 recently as a bicycle to ride in TDA (http://www.tourdafrique.com/tours/tourdafrique)
- disc rotors (side effect of changing wheels not for own purpose)
- added rear rack
- added both handlebar grips and bar extenders for more hand positions
Not all that is necessary for a shorter touring, but for doing some touring I'd definitely consider a rear rack, saddle and additional ways of getting hand positions. I rode the modified bike on a three-day 230 mile mini-tour weekend the before last and was a fun ride.
As far as parts go, it also depends some where you go. For standard touring I'd probably bring enough to deal with (a) replacing/patching tubes (b) spare tire if I was going far enough (c) spokes if going far enough. For trip I'm planning, I'll likely bring enough spares to rebuild a wheel, replace the drive train or cables or pedals. I'd also bring random things like extra seat post clamp and extra screws on racks, etc. I'd also double on wear items like chains and tires/tubes.
As far as past failures I've had on touring bikes (not necessarily Trek 4500), somewhat from most common to least common:
- bottom brackets
- seat post
I tend to bring enough to deal with failures closer to top of my experience list and when things lower on the list happen - I figure it out as I go along. How far down the list I prepare for depends on the destination.
Anything can break on a tour, as mev shows on his list. Best idea is to replace cables, brake pads, tires, tubes, and chain. If your cassette or chain rings are old replace them too.
Carry one tube and and a patch kit. If your tires are not touring grade, add a second inner tube. I like SRAM chains with power-links, and carry an extra link. A couple of spokes or fiber spokes are a good idea too. Replace any other part that you'd consider carrying as a spare, and leave the old component home.
I carry spare inner tubes (2), tyre boot, brake/gear cables, chain masterlink, 3 or 4 spokes. On longer tours I carry a spare set of brake blocks (because modern blocks need cutting to fit my old bike).
A few spare M5 bolts, zip ties, ductape, wire should get you home through most other failures. I cant think of any other spare that you would carry unless you are crossing a vast wilderness on your own.
Where are you touring? Crossing the US and crossing some remote third world country can be very different propositions I have found that as I tour more and more frequently, I carry less and less spares and replace less and less before the start. On any trip much over 1,000 miles I am likely to replace tires, chain or whatever at a bike shop somewhere along the way rather than replace stuff prematurely before the trip.
At a minimum carry a few spare spokes, a couple rack bolts, 1 or 2 tubes, and a patch kit. That is about all the spares that I carried for my last tour (Southern Tier).