What PSI should my 51 max PSI tires be?

 

I would think 32psi range

 

whatever the sticker on the door jam says

 

Open the drivers door you will decal plate, it tells you tire pressure!!!

 

If your tires are the same sizes listed on the sticker on the door jamb (or door), go with the tire pressure shown there.

If you have other sizes on the car, then it's best to go from the gawr numbers shown on the sticker and published load/tire pressure charts. If the manufacturer of your tires has a chart for your tires, go from that. If that's not available, go from the "industry standard" charts from the Wheel and Tire association. Generally you can find those with an online search for "tire pressure chart" followed by the exact tire size (including the "P" if it's present before the section width number).

 

I have a 1972 Honda CB750. It has a tire pressure listed. What I have learned is the listed tire pressure is calculated on the tire design and not the car design. The new tires for this old bike call for a higher pressure than the original spec. So, I would suggest checking with the tire manufacturer as opposed to a spec considered correct for tires of a design from a quarter century ago. Dan

 

I agree. Contact the tire manufacturer. I contacted Nitto and they recommend a higher PSI than the original tires that came with my '90.

 

If you're running the stock size (s) on the original wheels, the sticker is still going to be correct. It's all about the volume of the tire and the mass of the air in the tire. The load (weight) determines the mass over air required to support it, and you have to squeeze the required mass of air into the volume of the tire. That determines the pressure. Heavier loads need more air to support the weight, and more air squeezed into the same volume means higher pressure.

Even though tire compounds have changed, air hasn't, and new tires have about the same interior volume as 1980s tires.
I'm guessing your wheels are larger than stock, with lower profile tires. The sticker is only valid for the stock tire size(s) mounted on stock (size) wheels.

 

For the old 750 what has really changed is the sidewalls. In 1972 all the tires were tube type and you could pry the tire off in less than 30 seconds. Now the tires are all tubeless (use with a tube for spokes) and requires a machine to remove the tire because the sidewalls are much stiffer. The tire pressure is designed for how much the tire squats down and how much squirm it has on turns. Both of these factors are not the same as tires from 25 years ago. The pressure has no bearing on tire size as 32 PSI is still 32 PSI whether it is a blimp or a wheelbarrow tire. Dan

 

From my research all 84-91 Corvettes say 35 psi regardless of tire size. For 92-96 it says either 30 or 35 depending on tire size. I was taught start with what the sticker says and adjust to what works best for you.

 

All good so far. However, these are not the primary consideration for the tire pressures recommended on the placards on automobiles. I'm less certain about motorcycles or wheel barrows, but the factors you are referring to are definitely only minor, secondary influences for tire pressure requirements for automobiles (and other motor vehicles with 4 or more tires).
The opening part of that is just incorrect. Nothing about "tire squat" or "squirm" in any way influences the selection by a vehicle manufacturer for an appropriate tire pressure for the stock tires and wheels.

Tire size has a major bearing on the primary consideration for tire pressure recommendations. That primary engineering point for the recommended tire pressure is load capacity. Once load capacity is safely met (with an adequate margin of safety above GAWR), there may be increased adjustments for the cars top speed, because higher speeds require higher operating pressures to prevent the tire from overheating due to sidewall flex. There may also be small adjustments upward for fuel economy (CAFE requirements) reasons. And there's always a "margin of safety" above the minimum required by the GAWR.

I'm not sure about what the load capacity of a wheel barrow tire at 32psi is. It's definitely much lower than on any automotive tire that would fit a C4 Corvette. But let's just look at C4 Corvette tires. For a 1995 model, the stock front tire (255/45R17) can support 1,488 per tire at 32psi. The rear tire (285/40R17) can support 1,587 pounds per tire at 32psi.

Now, if you go +1 on the wheel size and run 18" tires, the 255/40R18 size can only support 1,378 pounds per tire at 32psi, and you'll probably want to increase the tire pressure to 35psi to get close to the same load capacity as the stock wheel/tire package. 35 psi gives a load capacity of 1,477 pounds per tire. On the rear, the 255/35R18 inflated to 32psi only supports a maximum load of 1,455 (SL rated tire) to 1,462 (XL rated tire) pounds, again, significantly less than the stock wheel/tire combo. Again, back there you'd want to increase the tire pressure, possibly as high as 36psi, for 1,609 (SL) or 1,606 (XL) pounds of load capacity.

Those numbers come from an industry standard set of charts/tables, but you can see most of them at https://tirepressure.org. Here's a direct link to the 255/45R17 pressure chart. https://tirepressure.org/255-45r17 and the 285/40R17 chart is at https://tirepressure.org/285-40r17 Those industry standard charts generally apply to most consumer automotive tires, with a few exceptions. If the tire you're using has non-standard construction of some type, for example, additional sidewall plies, then the tire manufacturer probably can give you a specific chart for their tires. If the tire manufacturer doesn't have a chart specific to your tire model, and the tires meet all the markings in the standard charts (SL/XL and the load index numbers match as well as the size, and the leading "P" or "LT" if present), then the industry standard chart should apply.

From the load requirements, for vehicles driven at high speeds with higher speed rated tires, there are minor upward tire pressure adjustments for speed. For example, for a "W" rated tire, you add 3psi for speeds up to 130mph, or as much as 7.5 psi for speeds over 150mph. Over 150mph, there's also a reduction in load capacity rating for W speed rated tires.

Finally, you should never exceed the maximum cold pressure on the sidewall, so in heavier vehicles. That upper limit that can restrict your top safe speed below the absolute speed rating of the tire on some heavier vehicles.

If you over inflate tires for the load for whatever reason (maybe to "stiffen the sidewalls" and make the tires less "squishy"), you'll also cause the tires to wear unevenly, and there can be other issues caused by the over-inflation.

 

Thank you all for the feedback. My apologies for the silly question, just bought new tires and want to treat them perfectly.