By Tony Marchand


Introduction:
The tire pressure as mentioned on our web site  tony10speed.com  depends on weight of the rider, width of the tires and road conditions. There is always a trade of between tire width and pressure. There is a debate about whether rolling resistance increasing with wider tires and lower pressure (probably a myth), but the ride comfort and handling improves. To high a pressure leads to decreased handling ability and more discomfort on rough surfaces.1,2 Rider weight as well as weight distribution has to be taken into account (45% in the front and 55% in the back for recreational riders based on my own studies using scales under each wheel)3. Use of Jan Heine's grafts and calculators based on those grafts seem to give a far lower pressure then the minimal tire pressure on most of today's tire.4,5 Today's type of tires where probably not available when Jan wrote her article.

1. Ideal Method for Measuring Correct Tire Pressure:6
Any method of determining ideal pressure takes the rider weight, bike weight, weight distribution and tires into account. Ideally, one should see a drop or compression of the tire to 85% or less. A number closer to 85% will give more comfort but one does not want to be below 85% because of the risk of pinch flats. A slightly higher compression of 90 or 95% may give lower rolling resistance but only on smooth road.


  • Place the bike on a smooth hard surface with the desired pressure in each tire. Using calipers, measure the shortest distance from the bottom of the rim to the floor. This distance should be a few centimeters in length.
  • Next (you'll need the assistant), sit on your bike with your hands on the handlebar and placing your shoulder against the wall. Have your assistant measure the same points, front and back.
  • Finally, for each wheel, divide the second measurement by the first measurement and multiply by 100. If both front and rear are 85 or slightly greater, you have ideal pressure for efficient cycling. If not, adjust the pressures accordingly not to exceed the tire maximum noted on the sidewall.
2. My Easy Rule of Thumb (maybe not ideal but gives a ball park figure):
  • Look at the minimum and maximum air pressure for your tire on the side wall.
  • If your a light weight (when fully dressed in your bike outfit and shoes and you weigh 100 - 120 lbs or less) aim for the lower end of the psi range, a mid weight (140 to 160 lbs) toward the mid range, and above 180 lbs aim toward the higher end of the psi range shown on the tire side wall.
  • Once you have selected an ideal pressure for you weight, adjust it to put about 5% less in the front and your ideal in the back (there is about 5% less weight carried on the front tire then the back according to my studies).
  • Do not go lower then the minimum or over the maximum on the tire sidewall.
For example, a tire with a minimum pressure of 95 and max of 120 written on the side wall of the tire:
Rider Weight (lbs) 100-120 120-140 140-160 160-180 180-120
Front Tire Pressure (psi) 95 psi 100 psi 105 psi 110 psi 115 psi
Back Tire Pressure (psi) 100 psi 105 psi 110 psi 115 psi 120 psi

Note:
  • Smooth road conditions allow for a slightly higher pressure and lower rolling resistance.
  • Lower the pressure by about 5 psi for very rough roads or wet conditions.
  • Raise pressure a few psi for cold outdoor temperatures.
  • Lower pressure a few psi for hot outdoor temperatures.
  • Experiment and find what's best for you.
References:
  1. Bicycle Tires and Tubes   from Sheldon Brown, Harris Cyclery.
  2. Tire Right Pressure   from Performance Bicycle.
  3. How to Select the Right Tire Pressure for Your Road Bike   from Active.com
  4. Optimizing Your Tire Pressure for Your Weight  Vintage article from Bicycle Quarterly by Jan Heine.
  5. Bicycle Tire Calculator   based on Jan Heine's work.
  6. How to Select the Right Tire Pressure for Your Road Bike  Tire pressure based on tire compression by Jim Castagneri For Active.com