I have a nice road bike now with aero bars.. always wanted to get a bike for time trials, but was curious about how much a difference they really make? The Time Trials around where I live are all about 13 miles in length and flat. If you own both a triathlon (or time trial) bike and a regular road bike:

1. Did you get a significant speed advantage with your Tri bike?

2. I know the 76 degree seat tube saves your legs for the running part of a triathlon, but if you are only doing a time trial, is this seat angle a disadvantage? I noticed the Trek TT bike Lance rode in the Tour has a 73 degree seat angle.

I have asked some people I have ridden with and have gotten varying responses.. on person told me that he is about 2 miles/hour faster on his Tri bike while another said she was able to complete a 13 mile course about a minute faster.

Thanks for you answers/advice in advance!

If you look at Jim Martins article archived on Cervelo's website then a aero frame is worth about a minute over 40K, making it worth about 30 seconds over a 13 mile TT.

http://www.cervelo.com/content.aspx?i=aerodynamics

Aero wheels would probably save another 45 seconds. You have to look at your results and see if that would make a difference to you. As far as positioning goes, some riders ride steep and some shallow. Lance rides shallow, but Hincapie rides on the front of the saddle and the whole CSC team rides pretty steep. Basso and Zabriskie ride at 77-78 degrees by riding on the front of a saddle that has the nose cut off to fit inside UCI rules. Landis is riding pretty steep as well.
I am going to be trying out riding steep and low this year in TT's, hopefully the better aerodynamics make up for my mediocre climbers power output.

All other things being equal, the fastest frame will be the one that lets you stay low and aero while maintaining power. Many riders (including myself) can do this on a 73-degree frame. The key is regular training to refine your position. There seems to me nothing inherently more aero about a 78-degree frame.

I got a separate TT bike at the beginning of '04. Before that I had clip-ons and semi-aero wheels on a 73-degree aero tubing road frame. The TT bike also has a 73-degree aero tubing frame, but with integrated aerobars and a zero-setback seatpost with forward saddle position. The improved positioning that allowed, along with the ability to train regularly in that position during '04 and some deep-V rims, reduced my 40k state TT time by 6+ minutes. Further training during '05 and the addition of a rear disc reduced my time an additional 2+ minutes. During those 2 years I have been able to gradually lower the front as I gain comfort. It is a radically different position than I could acheive on my other road bikes, even though the frame ST angles are the same.

Here are a couple of examples of positions from the TDF.

Zabriskie-steep

http://www.cyclingnews.com/photos/2005/tour05/?id=tour051/JD05tdfstg1_zabriskie

Lance-shallow

http://www.cyclingnews.com/photos/2005/tour05/?id=tour051/cycling-tdf2005-itt-arms-62

Landis-steep

http://www.cyclingnews.com/photos/2005/tour05/?id=tour051/cycling-tdf2005-itt-land-55

I think it depends on the rider, a bike that allows a range of positions might be the best bet.

Otherwise your really not going to gain any advantage because you will utilize the same muscles you train with, and with a different position just a little bit of discomfort will suck away any aero advantage gained.