Belichick your bike: Seriously, You Will Thank us Later
Over the course of the last week, we’ve been inundated by the so-called ‘Deflate-Gate’ resulting from the Patriots rout of the Colts in the Playoffs. We’ve taken our share of random phone calls, Twitter and Facebook questions, and even some suggestion that we should sell some SuperPista Ultimate LP pumps to the NFL (which we would happily do if they are interested BTW).
The overriding question has been, ‘why would 2psi matter anyway.’ Which is a questions we get a lot from cyclists about their tire pressure, so we thought we could tackle this (pun intended) from both directions.
- Grip: Lower pressure means greater flexibility in the casing of a tire, or a football. For a given force, the casing is better able to conform to the road surface (or the fingers) allowing for more grip, which equates to better control between the tire and road, or ball and hand.
- Impact: This one isn’t discussed as much, but especially if it’s cold, you would much rather be hit in the hands, arm, chest, whatever by a 10psi ball than a 14psi ball. The lower pressure and greater conformity of the ball extends the time over which the impact occurs and also allows the ball to achieve greater peak surface area. A football might be easier to catch as the time between impact and rebound between say the ball and your hand could be extended by micro-seconds. For the keen cyclist, all of these factors remain true, however, they are amplified over hundreds of thousands of tiny impacts as your tires roll over imperfections, road seams, pebbles, chip and seal, sticks, rock, etc in the road or trail. Reducing pressure by a few psi not only reduces peak impact forces of things you might high like pot-holes, but has a very large cumulative effect by reducing overall fatigue in the entire body.
- Aero: Nobody is talking about the effect of inflation on size, but a 10psi football is a few mm smaller than a 14psi football. Theoretically you can throw it faster and farther than a larger ball in the same atmospheric conditions. Similarly, your tires grow in both height and cross section with pressure. For example, a 23mm Continental GP4000s measures 24mm wide on a Zipp 404 at 100 psi and 25mm wide at 120psi. This results in an aero penalty of more than 1 watt 30mph, which may not be a large number, but at the same time is larger than the savings you would realize by swapping your wheel bearings to the highest grade ceramics.
- Crr: Also known as coefficient of rolling resistance. This one has nothing to do with football and everything to do with cycling. On non-perfect surfaces (ie, the real world) Crr decreases as pressure increases, up to a point, and then begins increasing dramatically again. The data show that being 5psi overinflated from your optimum has a greater penalty than being 5psi underinflated, and our survey data show that if you are reading this, you are most likely over-inflating your tires as over 90% of cyclist are statistically likey to be over-inflating!!
So we say, go ahead and Belichick your Bike before you head out today. Drop 2 or 5psi and see what you think. We’ve provided some rough guidance based on Crr data for blacktop/asphalt in good condition, try starting here and see how it really feels to drop a few psi.
Rider weight 120lbs, 23mm tires, average pavement: 80-95psi
Rider weight 160lbs, 23mm tires, average pavement: 90-105psi
Offroad and CX are significantly more complicated, but the experimental protocol is the same, try 2psi less and if you like it, try 2psi less again..you might surprise yourself.
PS, we had some fun with the title here in the hopes of getting your attention, but have no opinion either way on the actual deflate-gate. The reality is that if the balls were inflated indoors at 70F and taken outdoors to 30F you would lose about a psi. My favorite quote on this comes from Colts CB Dwayne Allen: ‘They could have played with soap for balls and beat us.”
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