Hi,
Originally Posted by
rekmeyata
Problem is the Michelin calculator (which is based on known calculations that have been around for many years), is that it's designed to give a particular size of tire and weight being carried the correct PSI for max wear and handling. Sure you could put more PSI in the tire then recommended but you will upset the proper PSI balance for the tire/weight combo and in turn the tire won't wear as long, ride as well, nor handle as well. Plus studies have shown that running too much air pressure will actually make the bike less efficient because the combination of streets not being smooth as glass and over inflation increases rolling resistance due to vibration being generated, and traction will be reduced due to the tire bouncing and could cause a bicycle to skid out of control on a turn, plus subject the tire to more damage.
See this for more detail, but scroll down to Width and Pressure:
http://www.sheldonbrown.com/tires.html
Sheldon, of course, is a great resource for all of these things (particularly because he was very good at citing and linking to his sources).
The only point on which I want to expand: While I understand that you can get away with a lower pressure in a bigger tire, how is that having 100 PSI in a 32mm tire going to give a rougher ride (in any sense - rougher, less traction, etc) than having 100 PSI in a 23mm tire. As soon as the tire is deformed because of imperfections in the road, the effective pressure in the smaller tire climbs much faster than the larger tire, making it handle bumps worse.
Don't get me wrong, I do think these tables are useful (particularly the graph on
the second page of this pdf file which is from where Sheldon got his numbers). And one reason these tables will tell you that you should put less air in a bigger tire is because you can get away with it and less air means more comfortable ride with more control/grip. But if you are going for speed, depending on the surface you are on, you may very well want to go above what they suggest.
Another way of looking at it, the OP was asking about
Conti Gatorskin hardshell tires. According to the manufacture website, everything from 25C to 32C can be safely run at 100 PSI. Assuming that the weight of the OP doesn't put him over 100 PSI recommended at 25C, then my original suggestion would be to go with the 32C and run it at 100 PSI instead of the 25. The tire will handle as well or better, have lower rolling resistance, and have the ability to be run at lower pressure when the situation calls for it. The only downside is the extra weight (where for both the OP and myself, the difference in tire size is really irrelevant).
It is completely relevant to point out to the OP that investigating lower pressure may not only result in a better ride, but lower effective rolling resistance for the reasons you bring up above. And again, the larger tire lets the OP have an (effectively) larger range of pressures that he try. And if you can get the same rolling resistance and a more comfortable ride, then I call that a win.
So, if the OP hasn't fallen asleep trying to read this thread, here's my advice: Go big!
Cheers,
Charles
p.s. Your point about weight distribution is good and largely missed by these discussions. It is worth getting a pretty good idea of your weight distributions and adjusting the tire pressures so the ratio of tire pressures is the ratio of weight distribution.