Is it irrelevant unless they say what size tyres they are using? Are bigger volume tyres/tubeless harder for a given PSI than smaller ones?
I'm sure my tubeless tyres are harder at 20 PSI than with an inner tube - is this because of the greater volume? My car tyres feel much harder at 30 PSI than my bike tyres at 30 PSI.
The construction of the tyre will also have an impact on how hard it feels - take a balloon and put 10psi into it and it will be squidgy. Do the same with a hard plastic box and it will still feel like a hard plastic box. So for a given pressure car tyres with stiff reinforced sidewalls will feel a lot harder than a folding bike tyre.
Yup it will vary between tyres to an exetent, like if you was using a tyre on your bike with the same wall thickness as a car tyre, you could probably drop to 5psi...
Yeah I thought different materials would have an impact - but what would explain the tubeless vs tubed difference?
Q - are tubeless tyres constructed the same as tubed tyres?
A - no.
QED
Yeah but there is less material not more in a tubeless setup - you would imagine having two layers of rubber would make the tubed setup stiffer.
Theory of tubeless running lower pressure is that it doesnt have the tube in there to pinch flat, a dedicated UST tyre has a firmer carcass to it as well.
Check out the Shwalbe (spelling?) website it has a study on rolling resistance at lower pressures, it seems at some point the RR can reduce, running lower pressure and large volume tyres over something pumped up hard.
Yeah but there is less material not more in a tubeless setup - you would imagine having two layers of rubber would make the tubed setup stiffer.
Yes and no, the UST tyres are a bit heavier duty, take Spesh tyre or a conti supersonic & 100G tube and the tube type could have less rubber in it than a UST,, all depends on what your comparing as you have kind of hinted at in the OP.
Yeah but I have done this with a ghetto setup with non-UST tyres - def felt harder than when I used the same tyre tubed.
Dunno grumm, if you have done a like for like, back to back test your in a better position than me... Does sound odd that the same tyre would have a difference you can notice by hand with or without tube, especially going the wrong way to your expectations. Perhaps your gauge isnt too accurate..
have they been pumped up with hte same pump?
I think a large volume tyre pumped to the same pressure as a low volume tyre will feel different under loading. Although the air in the tyre will exert the same psi on the tyre wall at rest, when the tyre is compressed/loaded, e.g by prodding with your finger, the large volume tyre will deform more for the same amount of force, I think.... ? This is because, if you think of the tyre being analogous to an air spring, you have to compress a larger volume of air to achieve the same increase in PSI as for the small volume tyre...
Maybe.
why not start by feeling the difference between the tyres off the wheel and not pressured.
OK let me explain - I am talking about having a tyre pumped up using my track pump with a tube in it, then taking the same tyre and doing a ghetto tubeless setup on the same wheel. 20 PSI in the tubeless setup feels like about 30-35 PSI did with the tubed setup.
poppa, not realy, the volume of a tire is huge compared to the volume displaced when its loaded against the ground.
if you ran both tires at 25psi and had perfect 50/50 weight distribution, both tires would need to deform to allow a contact patch equal to
ap=m (area x pressure = mass)
So for a 190lb rider with 25psi in the tires would have a contact patch of 7.6 square inches, on a 2.35 tire this would be 1.6inches long at each end. On a 1.9" tire it would be longer and narrower. And the contact patch for a (failry fat i'll admit) roadie is an inch square at each end.
OK let me explain - I am talking about having a tyre pumped up using my track pump with a tube in it, then taking the same tyre and doing a ghetto tubeless setup on the same wheel. 20 PSI in the tubeless setup feels like about 30-35 PSI did with the tubed setup.
Yep I get you and it cant...must be another variable somewhere..
who cares?
just pump it up to what feels right and ride it.
yup.
Yeah, but if you load the tyre by sitting on the bike, the pressure in the tyre will rise under the load and the air in the tyre will compress slightly. This effect would be more pronounced in the small volume tyre as there is less air to compress. Hence the small volume tyre would end up with a smaller contact patch. The difference might be tiny in practice though...
I am fully willing to be pointed at and told I am talking bowlocks though.
Some people on this thread think too much. 
I am fully willing to be pointed at and told I am talking bowlocks though.
Not talking bollards, but not what the OP was about..
who cares?just pump it up to what feels right and ride it.
I do, that's why I posted the thread. It doesn't really matter obviously, was just interested. Why did you open the thread then feel the need to comment on it?
With ghetto tubeless isnt the tyre seating against the tube rimstrip. Could this be deforming the tyre and making it feel firmer. I know from experience that tight fitting tyres feel less flexible than loose fitting after they are on the rim but before they are pumped up.
Did you do any kind of rolling test when you swapped to ghetto? be interested to know if it rolled further for a given hill etc??
With ghetto tubeless isnt the tyre seating against the tube rimstrip. Could this be deforming the tyre and making it feel firmer. I know from experience that tight fitting tyres feel less flexible than loose fitting after they are on the rim but before they are pumped up.
Hmm that might have something to do with it.
Did you do any kind of rolling test when you swapped to ghetto? be interested to know if it rolled further for a given hill etc??
No - I don't care quite that much
No - I don't care quite that much
But that was the important bit, no?
Are bigger volume tyres/tubeless harder for a given PSI than smaller ones?
Not totally irrelevant
Only important enough to post about on the internet when I should be working.
How would you go about doing such a test? Can't really imagine it being very scientific.
True poppa... 
placebo effect
Take bike with tubes to a small hill and roll down it see how far you go before stopping..... Take same bike without tubes but same tyre & pressure, roll down same hill see how far you go. Might want to do a few repeat runs get an average, and try the same on road and offroad see if you can quantify the Shwwalbewable site...
OK its not too scientific, but cant think of a better test without expensive equipment..
edit... be nice if the mags did it for us... hint hint.
i may ALSO be talking bowowks, but:
your indicationof PSI is based on how hard the air is pushing out of the valve stem.
NOT how hard the tyre is.
COULD it be affected by the air having to stretch the inner tube as well as they tyre?
x
Hmm... not sure about that - but maybe the pressure reads lower on the tubeless setup because the gunk is partly sealing the valve and the air isn't coming out as hard?
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