I had not known that tyre pressure would be relevant to understeer, or I had forgotten ...
David is CORRECT that one should check tyre pressures oneself.
Volvo specify different pressures according to load, and front v. rear and if I remember correctly, according to speed.
Interweb "wisdom" says under steer can sometimes be tyre pressure corrected by varying front v. rear pressures.
I am cautious of interweb wisdom including frums. One learn in whom to trust ... 
Comrade Stephen Edwin
.