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ASK RBA: ASK RC: TIRE PRESSURE
Richard Cunningham
May 12, 2010
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(Photo: Yuzuru Sunada)
I have been riding road bikes for 40 years and usually I keep the tires inflated to around 100 psi (I weigh 157 lbs.). Now I read that the pros use less pressure and that a lower pressure reduces rolling resistance. Lower pressures give a softer ride but I always felt that higher pressures allow the rider to go faster. What do you think?
–Paul
100 psi is about right for a 23-millimeter clincher tire. Tubeless tires are rated a little lower (90 psi), but you are in the sweet spot at your weight. Rolling resistance figures are measured by tire factories on smooth surfaces (steel drums, so the rolling resistance goes down as tire pressures increase up to a certain level where the tire is rock hard and additional pressure only forces the tire out of round. In the real world, however, the tire rolls over a barrage of irregularities on the road surface, so over-pressurizing the tire causes it to bounce over the bumps – which converts some of your forward motion into vertical acceleration. This wasted motion robs your energy. This means that choosing a pressure that allows your tire to deflect and compress slightly as it encounters bumps and rough pavement will result in lower rolling resistance. To soft and you will flex far too much of the tire and tube – which will produce friction and increase rolling resistance, so a balance must be struck.
Every tire has its sweet spot. Generally: for racing clinchers (Continental 4000, Schwalbe Ultremo, Vittoria Open Corsa), 100 to 105 psi seems to be the best pressure for a 160-pound rider. Heavier riders must use more pressure to prevent too much casing deflection and lighter riders need less pressure to achieve the same riding and rolling characteristics.
Contact Richard Cunningham for questions or comments, or just to talk bikes at: askRC@roadbikeaction.com |
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