I have a 2014 Giant Trance with an Overdrive 2 tapered steerer (1-1/2 - 1-1/4). As we know, the standard tapered steerer is 1-1/2 - 1-1/8 inch. I want to replace my OEM fork (Fox 32 Float Evolution CTD 140) with a more advanced Fox or RS. Is it possible to fit the bike with a standard steerer? I know that it would mean changing all the front end of the bike (fork, headset, stem) which I am prepared to do. Is there a headset to accommodate my frame and new fork. Would a standard tapered integrated headset do? Has anyone have an OD2 Giant bike here that have done the same exercise? This bike is problematic!
You can just buy a standard tapered headset. Or if you can firnt it, only the upper assembly for 1 1/8". Giant uses the same diamete for their 1 1/8" and 1 1/4" headsets as it says here: http://www.pinkbike.com/news/Giant-OverDrive-2-Steerer-tube-sizing-2011.html.
Another solution I can think of is to turn a spacer yourself (or have it done by someone) to work as an inner race for the bearing. It's more demanding (since you would have to turn both the spacer and a cap), but could probably work out a bit cheaper than the entire headset.