I am a big fan of 909s. There is a segment of the race populace who are concerned with wind problems with a rear disk but for any rider over 140 pounds, especially if you are on 650c wheels (I am), I think a disk is the way to go. Hills and wind are almost not a factor for the modern disks that are lightweight and stiff. I have won three USCF State Time Trial Championships on a rear disk in a variety of weather conditions including a nasty, gusty on again/off again rain squall. I think it only made me faster, especially when others were at their cars pulling their disks off. IMHO, FWIW you can't beat 909s. They rule.

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Tom Demerly
The Tri Shop.com

I'm with Tom here. Maybe I'm just plain dumb, but I've never understood the argument for not using a rear disc in the case of high winds. These wheels are supposed to be faster by virtue of them being more aerodynamic than spoked wheels. Meaning that they produce less drag as air moves across them. Wind, being air, blows across any wheel one might choose to ride and thus drag is produced. But again, a disc has a lower coefficient of drag than other types of wheels. So wouldn't it follow that the benefits of a disc would be enhanced by windy conditions??? In fact, (anecdote alert!!) the only time I've ever "felt" my disc to be much faster is in strong headwinds.

I understand that strong and unpredictabe crosswinds can make bike handling a touch scary. However, I've found that since so much of my weight is over the rear wheel, the effects of strong crosswinds on a rear disc aren't anywhere near as scary or difficult to handle as the effects of those same winds on a moderately deep front wheel.

You can't go wrong with the 909's, unless you want to save money and get something nearly as light in the rear and lighter in the front. I would get a Renn disc with a Nimble Fly front. That is, unless Frank gets that front wheel out sooner.

In addition to what Tom and Pooks said about discs, my opinion (which is shared by a growing number) is that the front wheel is your major factor in handling. I will also add that I felt that I needed a smaller section front in a very windy race I had competed in and the disc was a non-factor in my lack of bike handling. My Lew was too deep. It is spoke count that is the factor in aerodynamics.

In summation: get the 909's unless you want to get some other things, then get the Renn rear/Nimble Fly front.

OK, not trying to be a broken record here. But I agree with bunnyman 100%. (Nice to see him posting, BTW) My personal belief is that if the wheelset you are buying is going to be your ONLY race wheels, then I wouldn't go with the 909s. The reason, as bunny mentioned is not the disk, but the deep rim on the front. I strongly believe that if you only have one front race wheel, it should be a more "all-conditions" wheel like Nimble Fly, Zipp 303, or similar less deep rim.

I only have one set of race wheels, and it is a disc/fly combo. I've been very happy with the combo on flats and hills and in very windy or calm conditions. I have used this setup in some very windy races where I was sooo happy I got the Fly instead of the Alps or 404 I had my eyes on. The next race wheel I buy will be a deep section front like a 404, or perhaps a trispoke.