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I have an idea what the answer is, but I will ask this question of those with more knowledge then me. I recently put new tires and tubes on a 37 and a 41 Packard. The tire walls say to inflate to 33 PSI but the owner's manuals say 22PSI and 28/32PSI respectively. What is the reason for the spec PSI being different from the sidewall PSI?

The original recommended PSI is a bit low, one reason among them being for comfort on the often poor roads of the time. Neither the low or high pressure will harm the car as long as you stay within the limits, but I would advise a higher pressure as it will make a difference to the handling. Now I do not know which tires you have bought but a good start would be to go on the higher end and adjust until handling and wear is acceptable; you can use a tire crayon to test for even contact. Some members on this forum have gone to much higher PSI on tubes and seem satisfied-It all depends on your driving conditions and the specific tire.

Thank you. Your answer is pretty much what I had in mind, but just wanted to confirm. BTW, I got Coker Garfields for the 37 and Coker Goodrich for the 41. Both are bias ply and tubed.

The number on the tire sidewall is the maximum pressure for the tire. It is not a recommended pressure.

The pressures in the owner's manual are for the tires fitted to the car when new, thus, deviating from them is not a crime. I think one reason people think they should run higher pressures these days is because today's cars ride like garbage. I am always bitching about that.

I have a car that was setup for the European market in which ride quality is a top priority. It is a better riding car than the most expensive American cars.

So I would still run what the Packard manual says except if the tire manufacturer has recommended differently.

I remember reading an article on the 58 Stude and Packard models and how styling wanted to have the cars appear as low as possible since lower and longer was becoming the styling craze of the day.

Article stated that styling convinced engineering to go with 14" tires because they would immediately lower the cars an appreciable amount and then wanted to go even farther on the Hawks and Coupes. In addition to the styling bits with chrome placements giving the illusion of sleek and long, they pressured engineering to lower the tire pressures to the absolute minimum that would be safe to use. That change would lower the cars another fraction of an inch.

The tire pressure change appears to be what happened because the 15 inch tires on the 57 and one 58 bare bones model that kept them had a recommended pressure of 26 front and rear while the 58 models that went to a 14 inch tire had a recommended pressure of 24 front and 20 rear for ordinary use. It is interesting what might be considered ordinary use (one driver and showroom maybe??) because in the service manual there are caveats to the recommended low pressure. 4 passengers it went to 26 front and rear and if there was expected to be sustained high speeds, up to 30 psi. I guess the long and low look was not important when the car was actually being driven.

The tire guide does state that the maximum on the sidewall is a cold pressure number. Once the tire is on the road running the pressure will rise. So the next consideration is what the rim is capable of handling. Over inflation will eventually show up as poor tread wear. I never liked over inflation because it beats the hell out of the suspension, frame, and body joints. As well, if the car has an expensive paint job all that hammering will cause cracking.

Packard had a good proving ground so the recommended pressures are probably arrived at after a good amount of study.