An admitted shoe geek waxes philosophical about running, triathlon, and life in general.
Comments welcome!

Tuesday, June 26, 2018

Under Pressure

A couple weeks back I posted about the Vicious Cycles Gran Fondo I had ridden in Ellensburg. I also mentioned that I was providing mechanical support for the BuDu Racing Moses Lake Triathlon the day before.

And I was astounded. 

Far and away the most requested service was use of the floor pump, whether they wanted to wield it themselves or asking me to do so. In fact, I think there was only one person that wanted me to do anything besides air up their tires, and that was replacing an inner tube (which then needed to be pumped up).

Just a little topping-off to be ride-ready, I asked what they usually ran in their tires.

"One hundred twenty." "One-ten." Oh my...

I'd look at them, look at the tires, and sometimes ask them why they were running the pressure so high. All they were accomplishing is rattling their teeth out.

I get it. Really. It makes sense that a firm (or in this case rock hard) tire is a faster tire. And if that tire is rolling on glass, or as near as you can get on a road equivalent, then yes, generally a firmer tire will exhibit lower rolling resistance.

It will also slide easier, and transmit less torque. But that's only an issue if you turn, hit the brakes, or want to accelerate. Not a lot of call for those shenanigans in a triathlon.

The facts are that the tire, in real world conditions, rolls faster when it's not so firm. And the rougher the surface (within reason -- we're talking about road surfaces here), the lower the pressure desired.

And as the tire carcass gets larger (as in a wider tire), the need for higher pressure to avoid a pinch flat (where the tire bottoms out on the rim when hitting a sharp object such as the rim of a pothole). It's a balancing act of enough pressure to protect the tube (and as the rider/bike weight increases, so does the required pressure) and comfort.

For standard road bike tires of 23mm width, 100 psi is plenty. I routinely run mine at 90-95. For 28mm tires, 85 is considered fairly high.

That number printed on the side of the tire is the recommended MAXIMUM pressure, to avoid the tire blowing off the rim.

So ease up, people!

Your dentist will thank you.

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