I had to put on a 28mm GP5K S TR on my rear wheel yesterday due to a flat on my 30mm one I had there. I measured width at 65PSI (31mm BTW on a 25mm internal rim width) and adjusted pressure based on the Silca calculator. I went and remeasured the front (29mm Conti Aero111) and it was at 31mm vs the 30mm it was about a five months ago at the normal 69psi I run it at.
I figure some stretch is inevitable over the life of a tire, but how many people adjust pressure based off the new measured stretched tire vs just keeping the original pressures you typically ran with? Silca has me dropping 2.5psi on 31mm (66.5psi new value) vs 30mm.
Absolutely no one! Your tyre pressure varies throughout the ride anyway so adjusting it by just 2.5psi will not be close to enough to make any kind of difference. Your system weight also varies throughout a ride and you possibly start heavier and loose weight along the ride. Which would mean dropping your pressures accordingly. So yeah, the answer stays the same, absolutely no one.
I get that, I’m just talking in general though using the same system weight. I use 90kg as a system weight, the pressure differences between 30mm and 31mm are 2.5psi according to the calculator for an inflation pressure. Maybe I should have reframed the question.
How many people have adjusted their initial inflation pressure due to tire stretch over time on the same tire that has stretched just a tad and now the calculator has a 2.5psi drop (which is not insignificant)?
I would say as a matter of principle, if you’re using a tyre pressure calculator that relies on Width As Measured, then yes it makes sense to update that measurement as required and use the updated pressure.
In practice, however, I would say it’s not worth worrying much about. The calculators are only ever rough guides at best, and have to make lots of broad assumptions. My take home from playing around, both with the various calculators and on the road (albeit entirely unscientifically) is that quite a wide range of tyre pressures actually seems to work similarly well.
Had never even considered this and would suggest taking a deep breath and allowing the tires to do whet they do. Just use the same pressure you do unless it’s some extreme condition that day but even then probably only a few psi — assuming whatever gauge you use can even manage the nuance
I don’t, I use a pressure calculator to get me in the ball park of pressure range then adjust up or down according to local weather and roads. I only measure a tyre once and if I replace like for like I don’t measure a new tyre.