Here's what I got from an older service manual. Tire pressures are pretty much adjust to taste; for 21" tires anywhere from 35 to 45 is safe, all long as you don't exceed the maximum stated on the sidewall of the tire, from there do you like a softer or firmer ride? The former might give a lower lap time, but the latter will yield higher range. Carrying 4 passengers and luggage on a road trip? increase them. Not many people do this.
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