ASK RBA: ASK RC: ANOTHER THOUGHT ON TIRE PRESSURE

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ASK RBA: ASK RC: ANOTHER THOUGHT ON TIRE PRESSURE
Richard Cunningham
June 7, 2010

(Photo: Yuzuru Sunada)

RC, thanks for the great columns and advice! I have a question concerning road clincher pressure. I understand the rationale for lower pressure – say 100psi (or even 90 psi for road tubeless), in that it will allow the tires to roll over vs bounce off of small pavement irregularities. However, what about the effect that has in absorbing the energy from the rear as it is driving the bike forward? Would lower rear pressures not just lead to more tire flex and thus dissipate some of the wattage that should be meant to propel the bike?
–Mark

Your proper tire pressure depends on your weight, the volume of the tire carcass and how aggressively you pedal. Set the air pressure too low and the tire will flex laterally with each out-of-the-saddle pedal stroke—and distort too much with each downward thrust. Also, you need enough air pressure to stabilize the tire while you are cornering and the loads are off-center across the tire carcass. I weigh 155 and run my tubeless Hutchinson tires at 105 to 100 psi for best results. I ride 23-millimeter tubulars at 120 to 125psi. For clinchers, start at 100psi (115 for tubulars) and then increase 5psi at a time until you can feel the tires begin to rattle and bump over small cracks and ripples in the pavement. Then back off the pressure in 5psi intervals until the tire rides firmly on the road, but doesn’t bounce and rattle over rough pavement. You want enough pressure to minimize the tire’s contact patch to reduce rolling resistance, and the tire should be firm enough to transmit a slight feel of the road to the rider—but soft enough so tire can roll over small irregularities without shaking your arms and body.

Note: Get the tire pressure right and a good lightweight tire will make a distinct rolling sound — listen for it when you pass other riders.

Contact Richard Cunningham for questions or comments, or just to talk bikes at: askRC@roadbikeaction.com

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