MadRhino wrote: ↑
Nov 30, 2017 7:20 pm
On pavement, you can ride wide rims. 2/3 of tire width is safe, and let you ride lower PSI.
It is a myth that high PSI is making lower rolling resistance. Every tire has its own specific rolling resistance that is optimal at a specific rim width/PSI ratio. Small volume does require higher pressure and the larger the air volume, the lower the ideal pressure is.
Then the wider the rim, the lower the pressure, the best the puncture resistance, the best the comfort and traction BUT, the less the resistance to a hit. That is why we have to be careful using wide rims off road, or when we ride hard hitting curbs and potholes. The best hit resistance is closer to a 1/3 ratio, because higher pressure is possible then, and the the sidewalls are round enough to do the job.
Ideally,... your tire should be inflated to not deform under load, with few exceptions. This maintains a stable, consistent and dependable contact patch, which affects handling and tire function INCLUDING rolling resistance and puncture resistance. Perhaps the first thing you notice when your tires are low, is that it's "soft",... not carrying the full load as it should. Then you notice the handling with that load,... that "wobble" on each pedal stroke, unsureness in a turn or unexpected deflection from road dips, bumps and imperfections, or maybe an "unsolid" stop. Perhaps you notice how hard it seems to pedal and move,... due to increased rolling resistance.
While it's true that rolling resistance is no longer reduced by increased pressure beyond the point that a tire no longer deforms, it is grossly increased by lower pressures to a point that a bike with a flat tire is downright tiresome!
The BIGGEST "myth",... is that lower pressures reduce punctures! Likely due to the reasoning that it can more easily "deform" around a puncturing object. While true, it also concentrates the puncturing energy towards the apex of that impact and deformation, and defeats the tires design and purpose. Puncture resistance is a design function of the tires carcass (TPI and material resistance) and construction (i.e. special resistant belts) that deflects and distributes puncture energy to a greater area surrounding the impact without deformation or failure,.... and obviously dependent on adequate inflation pressure. A tire that deforms dramatically under impact, also increases the likelihood of "pinch flats" and rim damage (of which tires are intended to prevent!). And of course, tire, rim and tube slippage that some will overcome with "rim locks" and such, instead of suggested inflation pressure.
"Skinny" tires have higher pressure due to the function of pneumatics, low air volume, and that contact patch. It takes greater psi to support 100lbs load on 2sq inches than on 3sq inches, without deforming. With high pressure, less air volume, and small contact area,... "road" tires can feel every nook, cranny, pebble and rolling imperfection of a road surface. The low volume, high pressure is greatly dependent on strong bead and carcass construction and proper rim design that pushes the limits of "blowout" failures.
"Fat" tires, with lower supporting pressures and large contact patch.... feel none of that. And that's the intended design function of such tires,.... stable supporting consistency with a large contact patch for traction and ride comfort on broadly variable surfaces, especially loose, rugged or soft giving surfaces, as well as streets and sidewalks.
And yes,.. there are those who run even LOWER pressures, for a bigger contact patch and greater support and traction on the softest surfaces. AND they endure all the inherent problems of low pressures as "an advantage"??? If ya need more tire,.... GET more tire!
You can put ANY tire on ANY rim you can fit it on! AND run any tire pressure you desire. Jus know that in many instances, extreme or otherwise, you may be exceeding the designed specifications of specifically engineered tires.