If the sidewall of your 4.80-12 size tires say 90 psi then that is what you want them to be when the tires are cold (after they have been sitting for a while like overnight). This is the psi rating that the manufacturer has tested and approved to be safe with the weight rating that is listed on the tire. The psi will actually increase some during travel due to heat build up but the manufacturer has already accounted for this.
The 90 psi rating is actually normal for that size tire. For... view full answer...
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