Have 225-60-r 15 tires on my 85GT with 44 psi max. What is the good psi ?? Seems 40psi ( cold) makes the car " rattle" and 35 psi seems soft ( like my head). Need the proper psi ( cold) for a decent ride. Replies please.

I have 225/55-16 rear and 205/55-16 front. I run right around 30 psi front and rear. And my favorite thing to do is rip thru turns on back roads.

The type of tire can make a big difference also....Some tires are still using 1980s technology......I am running General G-max tires. They are an All-season performance tire and yet not too expensive- Tire rack testing rates them very highly.

Fiero and many other cars w/ OE tire sizes need 30psi.
Most alt sizes need same psi because most "big" tire size isn't big enough to matter.
Most "books" w/ pictures showing over/under inflation vs tire wear are useless unless way over or under for a long time.

"225-60-r 15" and other sizes is only part of story...
Changing brands or models of same brand can affect your ride quality given tires get same psi.

If you have suspension problems or worse mods, likely that is or adds to your problems.
Example: Lower cars often use OE size shocks and struts and run both out of range. Monroe w/ slotted tubes often will see more of that but Any brand can bottom out travel and have problems or ultimately destroy them.

I use 32-33 psi mainly so don't need add psi as weather temp drops during cold days. Most car tires add/subtract 1psi as weather changes 10°F up/down and weather is crazy this winter. This week says 30° last few days to 70° by Thur...
In "summer" ~ 31 psi just so don't need air every couple weeks to stay @ 30.

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(Jurassic Park)

The Ogre's Fiero Cave

According to the tire pressure calculator if you change from OEM 215 x 60-15's rear tires to 225 x 45 -17 rear tires the pressure must increase from 30 psi to 34 psi .

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My opinion (take it for what it's worth...) is start at 32 cold. These cars are light. The 44 you see on the sidewall is for maximum load handling. You don't need that, it will ride like a truck and burn the center out of the tire tread. Pay attention to your rire wear. If it looks like the edges are wearing excessively, add some air. If it looks like the middle of the tread is wearing faster, take some out. You'll probably find that 32 or so is pretty good.

Thanks guys for all advice. Will do 32 psi and enjoy the ride without the rattles. Was doing 40psi, now I know better thanks to you guys.

And to expand on that for a moment: 32 or 32-to-35 is most likely what was recommended by GM on the little sticker on the door jamb. I'd go check mine, but it is at home and I am at the office.

Sometimes that number varies wildly from what is marked on the tire. The Ford Rangers we used to buy here at the shop came with Firestone tires marked as 45 PSI maximum.... But the sticker on the door called for 25 PSI. Quite a variation.

I can't remember for sure but my 85 2.5 sticker said 2.4 or 2.5 bar on both axles which equals to 35-36 psi. That seems pretty high around here, so that's why I remember the whereabouts. Most cars around here have 2.0 to 2.2 bar depending on passenger number, luggage or no and which axle front or rear.

The "45 PSI Max" on the side of the tire is the MAXIMUM pressure....Not the pressure you run the tire at. My 1985 Fiero with 215/60-14 tires was labeled at 30 psi. on the door sticker; Remember that as the tire heats up the air pressure will go up......30 psi (Cold) becomes 38-40 psi on a really hot day with a bunch of corner turning.

Supposedly, the only tires that run at close to their maximum air pressure are trailer tires.

On my Uplander van, the recommend tire pressure is 35 psi......I run 35 on the front tires but dropped the rear tire pressure to 32 because of the light load- otherwise the rear tires will wear out in the middle. I got 40,000 miles out of my General Altimax tires.....and I actually replaced them because they were getting old (6 years)- not because the tread was wore out...

The reason that most vehicles have only one tire pressure for both front and rear tires (Even though the FF Vehicles have weight distribution of 60% front/ 40 % rear (Or worse) is because the manufacturers think (Correctly) that most customers are dumber than TWO boxes of rocks and having two different pressures will lead to confusion and mistakes...(Most people nowadays can't even change a FLAT!!!)

Yes, The "45 PSI Max" is Max in a Cold Tire and not driven for Several Hours at minimum. Preferred parked overnight & check in morning before sun heats one side of vehicle.
Sticker/book inflation is same, Cold Inflation.

⚠️ Max Cold inflation will change from tire model etc. Always check sidewall before pushing inflation up.