I am looking to get in to TT and would like some advice about what is the best bike for a beginner? Also, is there a difference between TT bikes and road racing bikes? Any advice would be great.
There are TT specific bikes but most people start off using a standard road bike, then maybe adapt it a bit, then if really keen get a TT rig, pointy hat etc. Best thing would be to enter a few local club TT's using whatever bike you've got or can borrow and see how you get on.
Most people start off on a normal road bike. The cheapest way to turn it into a TT bike is to get some clip-on tribars, as that enables the rider to get a more aerodynamic position. That way you find out if you like doing time trials and if you want to start spending money on specialist kit.
You can spend as little or as much as you want - from doing it on a normal road bike, then add some cip-on tribars or go all the way up to a TT-specific bike, skinsuits, aero-lids, overshoes, carbon wheels... the full works.
I used to TT on my road bike - skinsuit, aero lid deep carbon rims, TT bars (the old Mavic adjustable ones were the dogs doodahs) got some good times...
It's changed a fair bit since I last TT'ed 12 years back, although many courses benefit from a road bike...... especially if it's a circuit that is lumpy with lots of turns, rather than a flat dual carriageway..... certainly suited the Cheshire courses......
To my underastanding, there are two reasons, to get you further over the bottom bracket for increased power output and to help open up your hip angle to avoid too much loss of power when you are in an aero tuck possition.
Have a look at Tri and TT bikes and the angle the seat tube is, vs a road bike, you will notice it is closer to the vertical. You can emulate this seat angle by using a "fast forward" seatpost, which is like an inverse set back seatpost (google it for detail) or by pushing your seat right forward on the rails.
Dont forget that when you push your seat forward, you close the distance between the bottom bracket and your seat so you may need to inch the seat up a bit. You may also need to alter the fore and aft possitions to optomise your hip angle.
In a TT while "comfort" is an aspect of fit, it should be "comfort" in the context that you can complete the TT distance while keeping your possition and form and not be shifting about out all over your saddle and having to change your riding possition all the time, not "comfort" in that you could ride the bike around all day, hence some of the set up on the TT bike will seem odd because they go against standard accepted road bike set up. In context, most times your going to be flying over 10-25 mile on this thing, not riding a hilly mountain stage race that will have you in the saddle 6-8 hours.
There are some longer TT distances and events such as Ironman distance Triathlon, not sure how they would set up, maybe they make compromises in terms of aero and power output for comfort since its a longer distance?
Rob3rt has pretty much summed it up - the only thing to bear in mind is that it is also shortening the distance from the saddle to the bars, so in some scenarios a longer stem can correct the distance.
To some extent the seat tube angle/position of the saddle over the bottom bracket is restricted by UCI rules, but you can get away with more under CTT. Triathletes have it easy and some of them ride stupidly steep angles such as 85 degrees although this is also to help the muscle groups in the transition from bike to run.