benefits of wheel covers / fancy wheels

Took me a while to find it again, but this is helpful:

???http://www.cyclingtips.com.au/2010/04/biggest-bang-for-your-buck-in-time-trial-equipment/

As the author notes, it's a little odd they didn't calculate a box rim rear wheel to a disc wheel, but it illustrates the expectations rather drastically. For an IM distance, if you use the front box>front 5 spoke conversion as a proxy, that's ~180 seconds saved.

the author puts it more eloquently than I:

Time Trial Wheels are getting into the expensive end of TT equipment spectrum, but they do provide some good time savings and look very PRO.  Having an aero front wheel will make the most significant difference and will cost the least of the two.  Most of you probably already have a set of deep dish aero wheels for racing anyway.  A rear disc wheel is one of the last items you should spend lots of money on if you’re looking for big savings.  However, if you want to look cool this should be the first item on your list  ;-)  A good analysis of different wheel types vs drag in different wind conditions can be found on the HED website.

Get the helmet!

Don't forget about the cool sound they make! That's an intimidating thing to hear when you're getting passed....

Yes, I completely forgot that!!!  --> Domination Through Intimidation 

lightness for hill climbs and a road bike

weighty discs for aerodynamic cutting through wind on flat course with tri bike.

I remember when I did my first tri on my old road bike and someone flew past on a beautiful Cervelo with carbon wheels and a disk It went whub whub whub with that doppler effect as it passed and I almost peed on the bike. This is before I knew that it was OK, mind you

Guess what I'll be riding this year? Cervelo P2 with carbon wheels and a cover. This sport is worse than crack.

What would you call too hilly? I can't think of any MDot courses a disc or other aero gear wouldn't be beneficial.

I'm pretty sure it's helped on my S80.

ugh triathlon is not Mdot.  There are 2 olympic races here on that has a total of 1300' of climbing

And I'm guessing T1 and T2 are in the same location.

I picked Mdot because that would be easy for anyone to reference. 1300' is a good deal of climbing in an Oly, but not nearly enough to consider losing the aero gear. Double that still isn't there. Rev3 Knoxville had ~1500' in their Oly and there is no way I'd recommend anyone lose the aerogear there. IM St George has ~6600 ft in the 112 there, more climbing per mile, and there is no doubt that one should keep the aero gear on that one (cross-winds would be another issue).

For average age-groupers, the rule-of-thumb I've seen is around 6% for the tipping point, as in 6% for an all-uphill race. Not just having hills of that grade included. And it's steeper for faster/stronger riders.