06-07-2011, 12:39 AM
davester wrote:
[quote=kap]
[quote=M A V I C]
A narrower tire is not going to produce a smoother ride. Less rolling resistance and faster, yes, but smoother, no. And the higher the tire pressure, the stiffer the ride as well.
Your assessment is right on the spot ... I am still feeling the jarring.
davester,
My bike mechanic suggested 110.
110 psi on a 25 mm tires means that you should have about 125 lbs rider+bike load on that tire to get the proper contact patch squish. That means you and your bike have to weigh about 280 lbs. There's your problem right there!
Using the chart below, if you weigh around 180 lbs and have a 25 lb bike then you have about 92 lbs on the front and 113 lbs on the back. Therefore, you should have about 80 psi in your 25 mm front and about 85 psi in the 28 mm back. Going slightly higher will decrease your rolling resistance somewhat, but not hugely. If you go a lot higher than this then the vibration of the bike caused by overinflation will actually INCREASE your rolling resistance (not to mention drastically decreasing your cornering traction and comfort).
Here's a link to another method of determining tire pressure, though I can't vouch for whether it is a technically sound approach: http://www.faston2wheels.com/f2/2010/07/...uidelines/ . This one would calculate out to 92 psi front and 93 back.
Unless you are a lot heavier than 180 lbs, 110 psi for a front 25mm tire is just ridiculous. Wonder why the mechanic tossed that number to me. I am no where 180 lbs. Thanks goodness! Now my bike with the rear pannier weighs more than 25 lbs. Heck, just the U-lock and the chain alone are already 15 lbs at least. Thanks for the chart. I'll work on some calculations.