mine are bob on....i can even tell when i have been a little spirited, am 2 up, or its hot by the increase in pressure (and suspect i am not far from seeing a decrease as it gets frosty). I am sure you could calculate this but the additional force downwards adding people or luggage will increase the tyre pressure as well - equal and opposite forces & all that...not done the calcs but suspect nobody is checking their pressure when sitting on the bike - well apart from with the tpms!