Bicycle tires get a lot of analysis and over attention these days. Conventional wisdom is that higher pressure and skinnier tires make riding faster, therefore easier. But that has been challenged over the past few years. As with everything the practical truth lies somewhere in the middle of all the techno race jargon. Those who watch racing report that riders in the big time are getting into huge (25mm) tires they wouldn't have thought to use a few years ago. I've been told that new road bikes are being offered with clearance for 35mm tires. What! A versatile road bike!?!?
The theory I have heard is that the wider, softer tires will absorb irregularities in the road surface without slowing. The smaller harder tires bounce against tiny irregularities and cause more resistance which we feel as "road chatter" in our hands. It makes some sense to me, I switched from 23mm to 25mm on my road bike years ago just to eliminate the vibration and my wrists are glad I did. Now days, I'm riding my Hillborne with 32mm tires on charity and group rides and find myself scrubbing off speed on irregular surfaces to keep off another's wheel.
Of course we can't leave this alone and just go ride our bikes, there has to be more analysis and electronic gadgetry to go with this. Along with the theory is a reconsideration of tire pressure.
Past practice among the elite of club riders is to pump up the tires has hard as you can. That's why some still use sew ups, they simply won't blow off the rim! The whole idea of optimal tire pressure has become codified. Jan Heine of Bicycle Quarterly has written extensively on the subject. It all revolves around the research of Frank Berto who suggests that tires roll most efficiently at 15% compression and, since the front and rear of the bike carry different weights, the front should require less pressure than the rear to achieve that optimum rolling resistance. Is your head spinning yet?
Don't worry, there's an app for that.
The Berto tire pressure app allows you to customize your tire pressure for each bike according to bike type, tire size, your body weight and any accessory weight on each wheel. Sounds great, it assumes that 60% of the load will be on the seat and goes from there. The numbers I came up with are downright scary. On 25mm tires it says I should be using 130Psi on the rear and 95Psi on the front; 35 lbs difference?!? As the tires increase in size the variation reduces considerably. I suspect that, like all things bike, the proportions are probably based upon the great racers, not the average person. We all know that spandex hamsters are beings without chests or shoulders and rely on tendrils for arms. For those of us who possess the forbidden body parts, the ratio should be different.
As if this whole thing isn't anal enough, I broke it down to 55/45 for my build, applied that to the original Berto chart and came up with 110/87 lbs. for a road bike. That's a little less scary but still kinda weird. Applying this to larger tires the variation is reduced to around a 10lb difference in PSI. Less general pressure produces less variance between front and rear.
All of this has conclusively proven that I have way too much time on my hands, but if this trend catches on I can see the future with everybody relying on the cell phone app to dictate their tire pressure, perhaps linked to a compression monitor (a lazer on the dropouts to measure the tires constantly) and spandex hamsters stopping by the roadside to feverishly adjust their tire pressure every ten miles or so.
It can be coordinated through our Recon Jet glasses to constantly monitor optimal progress towards imaginary Strava prizes.
Or, we can swallow a bit of the Kool Aid, say screw it, run a little less pressure in your tires, a little less than that in front, and pedal merrily along in our golf shirts and dollar store glasses.
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