Originally Posted by
mpetry912
I would not say it turned out to be wrong, just not best. back in the 90s Jobst Brandt did a test on avocet tires that measured rolling resistance as a function of tire pressure. Those tests were run on a drum at (I think) Calspan laboratory which is a DOT sponsored vehicle safety and testing facility in upstate NY. A search of rec.bicycles.tech would probably find that test.
here's a long thread from THIRTY YEARS AGO on this topic.
Tire width and rolling resistance. (google.com)
There was in fact a small reduction in rolling resistance for pressure increases above 100psi.
- HOWEVER -
Real roads are not smooth resistance drums. Tires that are rock-hard can be downright uncomfortable to ride, especially on less than perfect surfaces. And we now have tires with wider cross sections that provide enough floatation to protect against pinch flattnig even at very low pressures.
So "the best pressure" depends on a number of factors including what feels right to you ! But for a typical 28mm tire on a common road bike, ridden in non competitive conditions, 80-90 psi is a good starting point.
I'm sceptical that a calculator or app can better determine the right tire pressure than I can do for myself. Remember air temperature has something to do with it too.
/markp
What Jobst Brandt of sainted memory was a good experiment, but it turned out to be an insufficient model of how tires behave in the real world, so I think it's fair to say the conclusions were wrong, or at least insufficient.
The two calculators I know of (Zipp and Silca) both say their recommendations are a starting point, and the rider should determine what works best. And while air temperature does indeed have something to do with it - PV still equals nRT after all - unless the temperature changes hugely between the time you pump up the tires and when you ride, the change is probably negligible.