Join Date: Feb 2007
Location: Tariffville, CT
Bikes: Tsunami Bikes
My understanding is that the helmet, kit (skinsuit or at least tucked in jersey etc), and body position count for the most. You compromise the latter when you move around to shift or drink or whatever. I'd buy a TT helmet - they put you into the right range of aero efficiency as long as the helmet fits your head/neck/back shape. Skinsuit is good or just wear that team kit that is just a bit too tight on you. Now the position - aero bars and height.
I bought again, in 2009, some of the original Scott clip ons for about $40. One bolt each side, skip the bridge to mount them closer. I never used them but I had this notion that I'd use them if I ever did a timed event on the track (I'm no TT guy - my one and only 3 km TT took me something like 5 minutes and change on regular bars). You miss being able to shift from the bars but it'd be literally 2-3 minutes to install or remove the bars.
If you want to shift from the bars, at least the rear derailleur, I'd install an inline cable breaker thing on your bike. It's used for the bikes with S&S couplings or the Ritchey Breakaway frame. Basically it's a detachable cable connector, allowing you to quickly remove your bars. Very light, aluminum, and good enough that I have friends who ride their S&S bikes all the time and they're equipped with the cable breaker thing.
In your case you'd put the inline cable thing only on your rear derailleur cable, probably down by the down tube stop (if you have a sub-bartape housing) or by the shifter (original style STI). Get a single shifter with the appropriate amount of cable/housing (terminating in another inline cable break thing) and stick it into the end of the clip ons.
Now add about 60 seconds to the 2-3 minutes and you'll be able to shift the rear derailleur from the bars.
I mention height too - if you really want to get into a good position you should get an adjustable stem to really drop your bars. The Look Ergostem is sweet (3 pivot points, including the fact that you can pivot the bars in the clamp) but the Ritchey and similar (two pivot points, same disclaimer) works well too.
I used a Look Ergostem to fit a Masters racer on a (literally) rusty old race bike he had - this was for the Masters "worlds" stage race in South America somewhere. In his case the Ergostem followed the head tube - the base bar was basically sitting just on top of his front brake caliper, and he had some long extensions so he could get enough reach. The plan was for him to either buy a frame that replicated the position or get a custom frame. Well he went and won the stage race (won the TT) and just left his bike as is, raced it as his TT bike until he decided to stop.
This will add another 4-5 minutes of swap time - just swap out the stem and readjust your headset. If you have any headset spacers you may be able to get a spacer clamp thing which keep the headset in adjustment regardless of stem position, although if you're dropping hard you may remove said spacer/s.
Finally, the long low position works best with a forward position on the saddle so your hip angle doesn't get screwy. Get a less setback post (zero if you have setback, a TT post if you have a zero). If you have a back up saddle mount it there. Add another minute for your swap time for swapping out posts.
Practice swapping the setup and definitely ride the bike in TT format. I don't know current protocol but in the past my euro-then-domestic pro friend told me he rides his TT bike 1/week minimum, more if he had an actual TT coming up.