Depending on the radial tire construction, some have even higher available pressures with no degradation in ride. Some of the newest "eco" type tires are way higher. Base it on the range suggested by the manufacturer--but there is a lot of wiggle room. I drive a VW diesel wagon as a DD, and it is usually loaded, and runs at higher speeds, so I run at 36 front and 41 rear which is the suggested pressure for loaded higher speeds; the usual pressure for regular driving is about 32. The tires deliver a smooth ride and last a long time even at these higher pressures.
Running on lower pressure to get a better ride on any vehicle is dangerous, as above, the "Ford Exploder" syndrome. If the ride is too harsh, then perhaps a different brand will run smoother.
