MartinC wrote:It seems intuitive to me that there's a relationship between pressure and penetration - so happy to take that as a given. What I don't understand is what other factors contribute to penetration and how they're affected by tyre pressure. Without knowing that I wouldn't like to say that I know the mechanism that predicts that lower or higher tyre pressures contribute to punctures.
I'm reminded of the old party trick - can you hammer a needle through a steel sheet. You can if you put the needle through a cork to support it. It's not the force from the hammer that's most important but other mechanical factors.
In my experience keeping my pressures high seems to reduce punctures and I know many others who echo that experience. But you're right - a simple model of pressure on the shard would seem to predict otherwise. On reflection I think that model's too simple.
I disagree, you can draw good conclusions from simple models with imperfect knowledge, as long as you know the order of the error you're likely incurring. You don't need to be precise to be able to make a call as to the likely trend. Simply: bit of rubber/kevlar and something sharp. The more you push, the more likely it is to go in. The only way that increasing pressure (i.e. increasing the push) would not result in higher penetration risk would be if there was a secondary (compensating) effect of greater order. I simply can't conceive what that might be, it goes against basic physics (e.g. less deformation might result in higher local pressure spikes->highly unlikely; lower pressures reduce deformation->highly unlikely). Thus I'll stick with my initial conclusions, while awaiting new knowledge. Occam's Razor and all that!
My experience is different anyway - the big jump for me with reduced punctures came when I started doing many more miles on 25mms as opposed to 23mm tyres previously (and the corresponding 15-20psi drop in pressure). If pressure played no role, then all other things being equal, I'd have expected an increase in punctures due to the larger contact patch (hence increase in road area/glass bits I was coming into contact with. That wasn't the case.
And anyway, this misses another massive point: if you're running 25mm tyres at 100psi, you're not doing yourself any favours in terms of grip, ride quality or rolling resistance!!!
