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Tire casing stiffness, air pressure & tire volume - Getting the best ride

by John Neugent

Tech articles | Commentary articles

John Neugent probably knows more about bicycle wheels than anyone else alive. Maybe more about bikes as well. He's spent his life in the bike business, at every level. He now owns Neugent Cycling, a firm devoted to delivering world-class equipment at the lowest possible price. If you are in the market for a set of wheels, please, check out John's site. He really knows his stuff. —Chairman Bill

John Neugent

John Neugent

For many years, and probably still today, pro tour mechanics would loosen spokes for the Paris-Roubaix. They thought looser spokes would result in a smoother ride. But they are wrong. Spoke tension doesn’t affect wheel stiffness.

Paris-Roubaix

Mechanics do what they can to make the stones of Paris-Roubaix tolerable. But looser spokes aren't one of the solutions. Sirotti photo.

A similar misunderstanding is now happening with tires. We measure tire pressure without a lot of concern for tire casing stiffness. Now that the trend is to wider tires, there is little real discussion about how that is affecting ride quality and performance. Stated simply, casing stiffness is a function of tire volume - as well as air pressure, and more than most people think. Yet there is no way I am aware of to measure it, even though it is probably as important as tire air pressure.

I just sent an e-mail off to Eric Hawkins, the owner of Park Tool about this. I have no idea how to make such a tool or even if it’s possible, but if one could be made, I believe it’s as important as air pressure.

We all know that car tires have relatively low air pressure – in the 30 psi range, and BMX and Mountain Bike tires are also much lower in pressure but still are very firm.

Below is a chart for 700 wheels. The tire size is the width of the tire. Tire stiffness is the same for all of them. It shows the variance in PSI to get the same tire stiffness. Now with 25-28 tires being commonly used, I would hazard that most people are overinflating their tires. Note that because there is more air volume, one can go even lower while safely preventing pinch flats.

Tire Size PSI
20 120
21 114
22 109
23 104
24 100
25 96
26 92
27 89
28 86
29 83
30 80

For non-suspension road bikes, which is what almost everyone rides, the tire is one of the primary suspension elements. There are now many articles written on the advantage of larger volume tires to the point where many pros now race on 25 mm widths and many people are looking for even larger tires. If they don’t reduce air pressure, they will lose all of the benefits.

John Neugent was was one of the first to establish quality hand building in Taiwan around the turn of the century. He now owns Neugent Cycling, a firm devoted to delivering world-class equipment at the lowest possible price.