A tire maximum load rating is reached when the tires are inflated to the maximum rated pressure stated on the sidewall. If you want to run them higher or lower it will affect the wear of the tire at maximum load, everything in between is up to individual preference and your need for a comfortable ride.
Personally I like them a couple of psi above the maximum rating but only because it gives a firmer ride and hence better handling. let your tire wear and likes dictate what you prefer, 28 psi will work just fine.
At our local track no street car is allowed on the track without 40 psi minimum in the tires because the cornering loads have a tendency to shred tires at lower pressures. Any tire pressure is only a recommendation not a requirement.
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