Redbullet

I think in my case everything is around average: my weight (incl. bike), road quality, weather (I always avoid rain/wet). I use 5 PSI below Continental recommendation for rear tire and 10 below for the front tire. It means 90 PSI rear and 85 PSI front. But still, these pressures are much bigger than the maximum recommended by website calculators (max. 78 PSI - "Rene Herse").
i remember that with Continental GP 4500/5000 - 23 mm I used 10 PSI below Continental recommendation. I used to trash 23 mm rear tires after around 9000 km and it was not due to rolling surface wearing, but due to side walls wearing.
The above suggests me that using the much lower pressures from the web calculators might decrease the life of the tire due to premature side wall wearing. At least for Continental GP 5000.

PeteHski

For my conditions Silca recommends 80 psi and SRAM 76 psi on 28 mm rear tyres. I don’t think the “one-size-fits-all” Conti 95 psi recommendation is anything like optimal for all but the heaviest of riders on narrow rims. That’s about what I would use with 25 mm tyres.

I am always conscious of the fact that running 10 psi too high loses far more speed than running 10 psi too low.

cuyd

All tires have recommended pressure listed on the sidewall, hence calculations for optimal values should start from there and (usually)should not go out of those ranges. Technically this is also true for some rims albeit it's harder to find data. For example one 23mm road tire could be 5-7BAR and other 9-11BAR. If calculator claims that 8BAR is optimal then you are not running tire to manufacturer specs. Of course this doesn't mean that bad things will automatically happen, just increases bad outcome chances.

PeteHski

This is not true. Sometimes they have a min and max pressure and sometimes just a max pressure. Obviously you should respect those limits, but they don’t help much with finding an optimal pressure.

prj71

It would be correct for me.

cuyd

All right, it's case specific scenario. One more thing to be aware of is that sometimes those values listed on sidewalls are effect of thorough analysis by company and sometimes those numbers are just what they think is safe(for them to not get sued). In most cases of higher end tires and reliable manufacturers those printed numbers are not random.

Koyote

No one is claiming that the 'printed numbers' are random. And the recommendations that will avoid lawsuits are probably arrived at through "thorough analysis."

PeteHski

Just to be clear, all tyres have a maximum allowed pressure on the sidewall and some also have a minimum allowed pressure. I haven’t seen any tyre with a “recommended” pressure on the sidewall.

For example my GP5000S TR has a maximum pressure on the sidewall of 78 psi. But that is not a recommended pressure for everyone to run. For most riders it would be well above the optimum for both speed and comfort.

Another example, my Pirelli tyres have both min and max pressures on the sidewalls. I can’t remember the range, but it is very wide. Pirelli do supply a chart with their tyres with actual recommended front and rear pressures for your weight and rim width and suggested adjustment for wet conditions.