Difference between road and TT bikes???

Apart from aero tubing, specific TT bikes usually have a slightly longer wheelbase, and sometimes a slacker head-tube angle, both which make the steering more stable, therefore the bike is more likely to hold a dead straight line with the sllightly less control the rider has using aero bars.

BUT, there's noting wrong with adapting a 'normal' bike for time trials. Aero testing shows that body position is the MAJOR OVERWHELMING factor when it comes to aerodynamics, and wheels is a very distant second. All the rest -- aero tubing, etc -- is minimal. I've read stuff saying that a tight, non-flapping clothing is more important than aero wheels, but I'm not sure about that one. 🙂

check out how body position affects speed:
http://www.legslarry.beerdrinkers.co.uk/tech/SpeedAndPower.htm

According to Hed, a "typical" 150lb rider in 'normal' conditions generates 6.5lbs of drag, and the best aero wheels reduce the drag to ~6.25 lbs

Usually your TT bike has a shorter head tube than your regular bike, giving you a larger saddle to bar drop. This allows you to achieve a better aero position with aero bars. You may also have to adjust the top tube length depending on where on your forearms you prefer to rest on.

A TT bike may also have a steeper seat tube angle, which allows you to rotate your hips a little and get a flatter back.

I use a smaller frame for TTing. Shorter top tube, shorter headtube, and a stem that is parallel to the ground rather than being angled up a few degrees like the one on my main road bike.

Turn your seatpost around to steepen the seat tube angle. Position in a TT is no.1

bobbyOCR said:

Turn your seatpost around to steepen the seat tube angle. Position in a TT is no.1

Are there any websites that talk about seat angles etc? how steep is the angle suppose to be? anyone got any pics?

There are some here: http://www.trysport.com.au/articles.htm
Also see: "Athlete Bikes" 😉

The pix below is one I set up for "Little jackie", it is about 78 degrees at the centre of the saddle.

Not sure if you've already read these but I researced these when I was considering the same thing. Do I modify my existing road bike or do I purchase new tri bike? If money were no option, I'd go the new one, but I've just added tri bars - more research - and adjusted seat angle. I ended up getting Profile Design bars as each bar is able to be adjusted in every direction ie length, width, height. There are spacers for arm rest height and they can be bolted to your bars wider to start with, then as you get more confident you can adjust them to a more 'aggressive' position. Anyway, you can make up your own mind. Also, I have a Bontrager Seat Post so that it can be turned forward for triathlon and then rearward for roadie.

Here's the links..
Aerodynamics of Cycling

Difference Between Road & Tri Bikes

Tri Bike Fit

Good luck with your research!