Originally Posted by
B1KE
Hey everyone,
I was reading some people run their tires in between 80-100 for a more plush ride. My current 25mm tires are listed as 110-125 PSI. If I run them under do I risk getting pinch flats, compromised speed/handling? What are the pros and cons of running below recommended tire pressure?
At 135-140 pounds, I've never pinch flatted down to 80 psi starting the week although that feels a bit squishy in back. 80-85 front 90 psi rear is better.
At 205 I never had problems starting at 90 psi front / 100 psi rear.
After six days they can be down 10 pounds and feel like they need air.
Continental GP4000SII tires roll well at those pressures. Less supple tires may not - pressure has a more significant effect as the carcass gets stiffer.
Obviously they feel better at lower pressures. Below the optimum pressure rolling resistance measures a bit higher, although too high costs you more than too low.
Dropping from 115 to 75psi here looks like .0005 Crr.
20 miles/hour is 8.9 meters/second; so a 75kg (165 pound) rider/bike combination would take an additional
8.9 m/s * 9.8 m/s^2 * 75kg * .0005 Crr = 3.2W which is about 1.5% of the 200W I use averaging that on a "flat" out and back course.
Most of your power is going into aerodynamic drag, with its force increasing with the square of velocity and power to overcome its cube. So at the same ~200W your speed would drop from about 20 MPH to 20 MPH * (197/200) ^ 1/3 = 19.9 MPH.
That's usually not interesting.
