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Tire pressure (Jobst Brandt)
The following is from Sheldon Brown:
"Rolling resistance" is the mechanical friction generated as the tire rolls. As a segment of the tire tread rolls into contact with the road, it deforms from its normal curved shape into a flat shape against the road, then back to the curve as the tire rolls onward. The deformation of the rubber in this process is what causes the friction.
There are two ways to reduce this friction, each subject to trade-offs:
The thinner and softer the rubber/fabric of the tire are, the more flexible they become.
The trade-off with this is that the thinner the tire gets, the more fragile it is, and the sooner it will wear out.
The higher the air pressure, the less the tire will deflect.
The trade-off with this is that if you pump the tire up too hard, you lose the benefits of pneumatic tires: the ride becomes excessively harsh, and traction will be reduced. In addition, extremely high pressures require a stronger (heavier) fabric and stronger (heavier) rim flanges.
Rolling resistance does decrease theoretically with any increase in pressure, but with modern, high-quality tires the rolling resistance at correct inflation pressure is already so low that the infinitesimal reductions gained are more than outweighed by the trade-offs.
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The only reason you would want to run the max rated pressure on your tires is if your a Clydesdale thus the tire needs the pressure to handle the load, this is assuming we're discussing 700x20 to 25 tires. Wider touring type of tires take the extra weight of touring gear into consideration, thus if you have wider tires and no touring gear then again you don't need max psi's.
Thus in summary a heavier rider needs higher psi's then a lighter rider on the same tire.
Like I stated earlier I only weigh 163 thus my rear psi is 110 on a 125psi rated Kenda Konstrictor tire, on the front I put in 100.
I also use Latex tubes which according to tests I've seen have lower rolling resistance then butyl, but it's a difference that I can't really tell but supposedly it's there; I use latex because they feel smoother and more comfortable, the sharp bang of broken pavement is reduce quite a bit, and chip and seal roads are less buzzy. This is the same reason people like to ride tubulars, which high end tubs use latex for the tube, you can pump them to 140psi yet will feel like a clincher with 70psi. Latex tubes cost a bit more then the cheaper low end Butyl tubes but almost the same as high end racing butyl. Latex does loose about 20psi overnight, but racing butyl tubes will loose about 10, either way your going to have to put air into both to ride the next day.
