While I agree that people should try to limit the weight and aero cost of carrying stuff on your bike, the abosolute most important aspect of IM is your nutrition stategy. If you get this wrong, it doesn't matter how much training you've done, or how light / aero your bike is, your body won't function how you want / need it to. First, work out how much calories you need and can consume per hour, and work out a nutrition plan accordingly. This must be practiced numerous times in training so you know what your body can handle on race day. Only then should you work out how you are going to implement your strategy on your bike most effectively. Ie - nutrition strategy comes first; weight and aero considerations second. (What's the use of having the lightest and most aero set up if your body can't power it properly after 4 hours?) Also, people overestimate weight cost over a *relatively flat*, undulating course like Ironman. Having looked at some of the data out there on the web, I estimate that every 100g of extra weight will cost you in the order of only 1-2 seconds in time, over the course of the entire 180km. (one study I read showed that unless you are climing an Alp, a bike that is 3kg heavier will cost you around 7 seconds over an undulating 40km TT). I'm more than happy carrying an extra 500g in nutrition and spares knowing that at i will lose 5 seconds on the IM bike leg! Far more important is where that nutitrion is placed so as not to have an aero cost.... (the study also showed that losing 3kg in body weight signficantly improved time over a 40km TT, but due more the smaller body surface area and lower drag than the weight... ) As for my set up I have three bottle cages on my bike - one mounted between the arms (BTA) and two mounted on an X-Lab turbo wing behind the seat. I will carry one bottle of carbo drink BTA, which will get replaced with GU Brew bottles from aid stations. Behind the seat, I will decant 8-10 gels with a touch of water into a small bottle to go in one of the cages (I find it quicker, eaier and less messy to take in gels this way than dealing with gel packets). The other rear cage can be used to carry water (picked up from aid stations) as needed - I need to drink some water with the gels, otherwise the concentration of carbs in stomach will gest high resulting in GI issues - and for drinking and cooling if hot. This will be half empty most of the time... Will throw one or two energy bars into a rear pocket and pick up chomps on the way for something chewable. Also, if I happen to lose my nutrition bottle, plan B = just eat GUs from aid stations. I also run tubulars with sealant, but will strap a spare tub between the two rear bottle cages with 2x bombs and inflator. This set up give me everything I need and is really pretty neat and it is all tucked away out of the wind. I will have no bottles on the frame or GUs / bento box taped to the top tube to catch the wind...
