Fork problem

[BikeLoverFromChina]

Hello, i want to convert my Centurion Ironman Expert into a time trial bike. its a 50cm frame. the problem is i have no idea what length steerer tube i need since i don't know how much thread is actually on the fork. I'm planning on getting a 160mm carbon threaded fork off amazon. do you think it'll work?

[Joe_W]

Considering just the radically different geometry of TT and road bikes and being very blunt: This will be impossible.
And here is why: The best you can achieve is a compromise between a road and a fully aero position. The main problem is that the weight distribution will radically change if you go to a really agressive aero position ( seat angle > 78° etc), making the handling very different, probably even dangerous. You can ameliorate this effect a bit (I guess) by changing the fork geometry (trail and rake), but ultimately this will remain a compromise. Check with an experienced frame builder who knows about stuff like that. Note that this is (in my opinion) the sole reason to change the fork (other than the old one being broken).

Usually a moderate Aero position can be achieved by putting on some aero bars, moving the saddle forward a couple of cm, lowering the handle bar and calling it a day (well, you'll have to play around with all the settings for some rides, eg. trying to clamp the aero bars under the road bar to go lower). The full conversion requires a huge investment (brake levers, base pursuit bar, aero bar, shifters, fork) and will (I fear) not result in a bike that is really a TT bike, but rather have the high risk of resulting in a difficult (maybe dangerous) to ride bike.