Depends on what you want to do. For autocrossing (stock class) I first weigh the car total and front & rear. Then I divide the max load of the front tire into the weight of that axle (1-1.1 gee cornering is about right if you want to be competitive) and multiply by the max pressure on the tire. Do the same for the rear and you have a good starting point.

Thutty yar ago Sunbird with a V8 in its nose ran A60x13s at 50 psi in the front. Two became baldinis every weekend. Didn't know about dangers of overinflation then but NP.

Crossie spec sheet says coupe is 3061 lbs 54/46 distribution so 1653 lbs on the nose

For street driving use 60% for a soft ride and 75% for spirited. Been using that for about 40 years now.

Front tires (stock) are marked 1389 lbs at 51 psi so the swag is 36 psi cruising and 46 for TOTD. That is where I'd start. Chrysler said 32 psi front cold so ballpark. What do others run and for what kind of driving ? Larger tires need less pressure.

ps was just looking at a '73 Goodyear tire sheet. Fronts were 10.35x15s which had a section width of 10.6" and an overall height of 23.4". I make that a 40. Did want a 10" rim but the SCCA said 9.5" max. No Big. "No trade in" price was $52.80 but no racer paid that. Sidewalls were so thin that you needed to air up every morning.

 

Absolutely correct !!!

 

OK back from Church & no flames so a bit more.

Figure that Corvette Front tire in '73 would be a 265x40x15 in todays vernacular so is really nothing new (and used to call them "erasers" cause the sidewall was so short).

Comment was made that only a few fuddies have original size tires. For serious driving more would be a good idea. Tirerack is a great resounce but don't forget they have lawyers telling them what to say so sometimes you need to read between the lines.

I used to run in SCCA stock class Solo II which means DOT tires with a wear of at least 200 so 1 gee cornering was enough, didn't need to build for 1.25 gees (forget high school physics, for a good tire/surface the "tractive effort" relates to fractals and not coefficients of friction).

Using the formula for the front stock crossfire tires on my coupe gives (51x1653/1389) 61 psi. Aside from needing high pressure valve stems, it is still not a good idea so need a tire that can handle a max load of 1650lbs or thereabouts. TR says a 235x45x18 is a good choice but is an inch larger diameter - will that fit ?

BTW fanatics might find this interesting.

BTW a similar exercise will work for the rear. Too much tire does not work either. Someday we can talk about "unladen understeer".

 

SKIP TO STEP 59 - Adjustment of the steering box - SKIP TO STEP 59

How to reseal a MB steering gear