The original poster said that his team weight is 400 pounds, 450 if the son is riding. Does that include clothing, water, and gear weight??? Two pairs of bike shoes weigh about 4 pounds, other summer-weight clothes probably add another 4 pounds (incl. helmets). Five full water bottles, alone, is another ten pounds. You carrying any food or gear on your rides? It's pretty easy to end up with ten more pounds (pump, inner tubes, multitool and repair kit are 2 pounds). So your team weight, fully loaded and standing on a truck scale, could easily be 425 to 475.

So I assume that all of you lightweight teams that are encouraging him to ride on the stock 28's will be contributing to his hospital bills if it doesn't work out?

The fact that DaVinci said to run on tires pumped up beyond spec is a little worrisome. Did you discuss your team weight with them? While it may have been true at one time that tire companies speced a max pressure that was half the blowoff pressure, the competition in max pressure has made it so that tire companies have an incentive to be less conservative. And these are not "tandem-specific" tires -- they're tires sold primarily to singletons, carrying much smaller loads.

A 700x32 tire is only fifteen percent bigger diameter, but thirty percent greater volume, and can be run at significantly lower pressures without risk of pinch flats. We run at 95 psi over all sorts of roads (including gravel), day and night. Lower pressure also means lower likelihood of regular flats, too. You've already had a blowout, so you know how much fun it is. A pair of 700x32 (or even bigger, since you have clearance) Panaracer Paselas costing $30 is pretty cheap insurance. To me, the relevant question is "A week's worth of latte's, or my life: Which is more important."

When I had Peter White build up a wheel for me (our tandem team weight is about the same as the original poster's) I asked what is the smallest size tire we could run on our Velocity Dyad rim. He told me that we could run a 25 in an emergency, and a 28 for a little longer, if we had to, but that in his view running anything smaller than a 700x32 with our team weight is flirting with disaster.

Nick Bull