Below is the recommended tyre pressures for the GS300 (1998 -). Many owners have found reducing the pressure by 2 or 3 psi improves the ride quality.
225/55 R16
Up to 100mph
Front 32 psi (up to 4 people) 35 psi (up to full vehicle capacity)
Rear 32 psi (up to 4 people) 36 psi (up to full vehicle capacity)
100 – 132mph
Front 33 psi (up to 4 people) 35 psi (up to full vehicle capacity)
Rear 33 psi (up to 4 people) 41 psi (up to full vehicle capacity)
Above 132mph
Front 35 psi (up to 4 people) 38 psi (up to full vehicle capacity)
Rear 36 psi (up to 4 people) 49 psi (up to full vehicle capacity)
235/45 ZR17
Up to 100mph
Front 33 psi (up to 4 people) 33 psi (up to full vehicle capacity)
Rear 33 psi (up to 4 people) 35 psi (up to full vehicle capacity)
100 – 132mph
Front 35 psi (up to 4 people) 36 psi (up to full vehicle capacity)
Rear 35 psi (up to 4 people) 41 psi (up to full vehicle capacity)
Above 132mph
Front 38 psi (up to 4 people) 41 psi (up to full vehicle capacity)
Rear 38 psi (up to 4 people) 49 psi (up to full vehicle capacity)
245/40 ZR18
Up to 100mph
Front 35 psi (up to 4 people) 36 psi (up to full vehicle capacity)
Rear 32 psi (up to 4 people) 35 psi (up to full vehicle capacity)
Above 100mph
Front 36 psi (up to 4 people) 36 psi (up to full vehicle capacity)
Rear 35 psi (up to 4 people) 35 psi (up to full vehicle capacity)