Manufacturers have a whole bunch of reasons for recommending a certain air pressure be used...ride quality, gas mileage, not having tires explode
None of which is about maximum grip...
"Recomended pressure" can mean a lot of things.
There' the maximum pressure printed on the sidewall. Lots of folks think this is the recomended pressure. It is not. This it the DOT-mandated maximum inflation pressure. In other words, do not exceed this pressure under any circumstances.
Now, if a manufacturer gives you a pressure recomendation for a street tire you can pretty much assume his priorities when figuring out that pressure are:
- Tread wear
- Performance (maybe)
For performance driving, I'd probably start at that pressure and work from there.
Now if we're talking about a race tire (or DOT-legal R-compound tire,) the manufacturer probably does have an inflation pressure he's going to recomend for the best performance. If you're lucky, he'll have several recomendations based on the car and its weight.
If you're lucky.
He almost certainly will have an optimum temperature range for the tire. that's the best thing you can use when tuning air pressures (and alignments.) You want to get your tire temps right, and you want them even across the durface of the tire, inside to outside (usually, but occasionally you'll run across a manufacturer who wants to see a different temperature profile across the contact patch -- the old BFG R1's were like this.)
So, go out and beg, borrow or steal a tire pyrometer and hit the track! Once you get the temp right, note the hot pressure. THAT's your target pressure.
(Unfortunately, that pressure is likely to change with the track, driving style, and weather, so don't take it as gospel -- keep that pyrometer handy!)