Stiffer sidewalls, lower pressure, supple tires, higher pressure; Grant's blog

[Patrick Moore]

Amen to this; I discovered this with consternation some 10 years ago after I swapped my stiff-walled Big Apples for supple-walled Furious Freds hoping to pump the FFs to the same ~17 psi as the BAs and get wonderful supple rolling and cushion. But I had to pump the FF 5 psi harder than the BAs to keep from wallowing and bottoming out -- which made the FFs feel just like the BAs on dirt. Of course, about a 1 cm width difference.

By "RTF" Grant means "roll flat technology" -- ie, stiff sidewalls.

There is a trend to tires with thin, supple sidewalls. But more supple means less RFT. When things are good, it's fine, but if you're going on a multi-week ride in rocky terrain and no bike shops, there's a good reason to ride stiffer sidewalls. 

With more RFT you need lower air pressure in stiffer tires to get the same cush for the same weight on it. Physicists may be able to prove on paper that that's a crappier way to achieve a cush factor of X, but to my bad brain, 45psi in a supple tire of a given volume or 30psi in a stiffer tire are going to feel the same. And the stiffer tire gets its stiffness from a sidewall that's not just stiffer, but thicker and tougher, too.

This is not an attack on supple, it's just another way to look at cush. On some rides, maybe you'll want to pump up harder and go with a stiffer tire because it's lighter and has detectably more zip? And on other rides, like daily commutes, trails, and tours, you might want a tire with more RFT. I wouldn't put supple tires on a workhorse. 

FWIW, here's a ceteris paribus stiffwall/supplewall comparo:

Big Apples, combo sandy dirt, choppy washboard and horse hoof damage, and pavement: 17-18. Comparable pressure for the ultra supple and light (make RH extralights seem heavy) Big Ones: 19-21.

And interesting background on the high-value retro-market MB-N mountain bikes. Grant explains how he's moved on. Makes sense. 

And there's a new Rivendell pump with wide wood handle at only $45 coming in October. I expect that will be my first floor pump purchase in a decade or more.

Patrick " but no interest in high-normal rear derailleurs" Moore

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Patrick Moore

Alburquerque, Nuevo Mexico, Etats Unis d'Amerique, Orbis Terrarum