Jason N wrote:
Is there a reason you wouldn't just choose one set of wheels (6/6, 6/9, or 9/9) and just add a disc cover. If this is for your TT bike, and you don't plan to road race at all, I'd go 6/9 with a cover. You'll be able to handle pretty much any situation with that setup, and you'll never be more than a handful of seconds of a disadvantage to the "optimal" setup for any given course.
As far as braking differences between aluminum brake tracks and carbon. I find that the newer carbon surfaces and pads have bridged the gap pretty well to aluminum in most cases. When it's wet, you do have to "scrub" the brakes a little earlier to remove some of the water on the pads/brake surface, but after that the braking quality is about the same. Slightly better with aluminum, but it's not like aluminum brake surfaces perform the same way in the wet as they do in the dry. So I would say it's more a difference in braking technique than anything else.
However, if you're going to be doing some crazy steep or long descents that require a lot of hard braking (wet or dry), then I would go aluminum brake track. The overheating on carbon brake surfaces can cause delamination...which I have seen first hand. This is not you're common types of descents I'm talking about though...would pretty much never be in a triathlon course, but something like a 10-15% descent for over a mile...where you have to stay on the brakes because cars can pull out of driveways at any time.
Agreed, I'd go for 6/9 or similar. Can't see it ever being worth getting 4 wheels! The situations where a deep front gets you a real advantage is also the one where you would use the shallower one, if ever. i.e. wind. If wind bothers you get a 6 for the front and forget the 9. Otherwise get the 9 and forget the 6.
As for braking and alloy versus carbon. If there is a disadvantage with alloy as you accept, even if it is small, then what's the upside with carbon? Aesthetic plus a tiny weight advantage in some cases? Surely then alloy is superior?
Incidentally, I do descend 10-15% gradients of over a mile in length very regularly. Typically I'm staying off the brakes but I do occasionally have to use them quite heavily depending on traffic, etc. So I have absolutely no desire to chose worse braking even if it saved me a few seconds....and I don't believe it would. In fact given some carbon wheel manufacturers expressely warn against using latex tubes, if I followed their advice I'd certainly lose time.
