Did my first ever tri on a steel 12 sp without aerobars and with box 36 spoke wheels. Was a sprint tri with a 34 kms bike split. I then did the course again on the same bike but added aerobars, clipless pedals and a pair of used aero wheels (28 bladed spoke, 30 mm rim) and took nine minutes off my first time.

The benefits of a disk are well documented -- for an estimate of the timesaving benefits over 40km on a flat, out-and-back course, play with the parameter settings at this excellent site: http://www.analyticcycling.com/...WindCourse_Page.html

As for frame/position aero benefits, I think my Cervelo P3 is probably 90 ticks faster over 40 km than my standard road bike, which is a Spectrum (custom geometry Merlin Extralight frame) -- much of which comes from improved positioning, rather than simply the P3's aero tubing and the seat tube that effectively masks the rear wheel.

As for helmets, the Louis Garneau is the closest thing I know of to a currently-manufactured USCF-legal aero helmet. I have one, but in my opinion it's not nearly as aero as the old Monarch Aerodyne fibreglass helmet I race my TT's in (also USCF-legal, but, sadly, no longer made). Probably 30 seconds less fast than the Aerodyne -- just my hunch form various courses I've done on both. The LG's "tail" is more truncated than the Aerodyne's.

The LG, in turn, will probably save you ~40-60 seconds over a standard helmet over a flat 40km course (you can save time even with a standard helmet by taping over the vents).

All these benefit guesstimates assume an average speed of ~27 mph (43.5 kph) over 40km; the Analytic Cycling link above will let you adjust an estimate benefits for other for higher/lower average speeds and wattage outputs.

40-60 seconds? Really? How is the ventilation on that thing? Does it have any?

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Animal!!!

Not much, except at the very front. What it does have you should probably tape over, if conditions warrant. The Aerodyne has none, but I've never had a problem overheating in it.

on my usual 25k time trial course:
1. aerobars are worth 1-2 min. This is relatively low, I suspect because this course includes some MUT riding with blind corners, tunnels, etc where I come out of the aerobars.
2. deep section wheels with low spoke count and bladed spokes (Zipp 440 front, Hed CX rear) are worth 2-3 min.
3. For some reason the Trek 2500, which has a sort-of-aero downtube, is a minute or so faster than an old steel Paramount. I'm frankly not sure what to attribute this to - probably a mix of positioning, better stiffness in the Trek for the multiple accelerations that the MUT requires, and maybe some aero addition from the frame ? The Trek has bar-end shifters and the Paramount is DT, so that may make a difference too.

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"It is a good feeling for old men who have begun to fear failure, any sort of failure, to set a schedule for exercise and stick to it. If an aging man can run a distance of three miles, for instance, he knows that whatever his other failures may be, he is not completely wasted away." Romain Gary, SI interview

that is an awesome site and thanks for the feedback. was your road bike fitted with aero bars by any chance? (that is my current set up but i was up at fitwerx (www.fitwerx.com) last week and am getting serious about body positioning and possibly a p3 myself...

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www.true-motion.com Triathlete Casual Wear since 2007
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That extra 40-60 seconds is probably coming more from the placebo effect than actual aerodynamic benefits. Guys like John Cobb have estimated the LG helmet as being about the same as a standard helmet with the vents taped over. And that's probably worth no more than 15 seconds in 40k.

Yes, road bike was set up with aerobars (clipons -- TTT), while my P3 uses VisionTech aerobars. Glad you liked that other site -- I found (and continue to find) it immensely useful. Let's you play with a ton of different parameters.

On the other followup: could be placebo, but I doubt it (even though I'm willing to concede that Cobb is the guru here). OK -- 50 ticks might be a hair high compared to a standard (non-taped over) helmet. But I'm certain (from having TT'd the same flat, 40km course over 100 times in the past 12 years using lots of equipment setups) that a standard helmet is at least 30-40 seconds less quick than an aero one.

Of course, not all standard helmets are equal, either. I have one that I love for its ventilation (the same model Euskatel-Euskadi race normal stages in), but its ridges stick up so high that it's a parasail it you try to TT in it.