10% rules applies to air but what about N2 or C02?
They don't expand the same way, so it doesn't really apply.
IMHO, tire pressure is a combination of factors and requirements. There is a wide range of pressure you can run without running into issues, but it heavily depends on the tire, the rim, the vehicle, and personal preference.
To use my vehicle as an example...
Toyota recommends (as per the door sticker) running at 32 PSI on P275/70R16 (this is based on the stock weight, as per the sticker). Since I've never run that size tire, this recommendation is fairly academic for me. But this recommendation isn't a "
run this or you'll crash into a bus full of nuns carrying a load of orphan children to the homes they've always dreamed of" requirement, this is Toyota's recommendation for the PSI to run that gives the best balance of control, comfort, and fuel mileage (especially the last one).
As a general rule of thumb, you can run a higher PSI to get better gas mileage or a lower PSI to get more comfort. Handling requires a balance of the two--too much and the tire won't flex and grip, too little and it gets sloppy.
The reason Toyota's recommendation isn't an end-all-to-end-all is because the PSI to run depends heavily upon the tire. A load range E will take far lower PSI and perform/handle exactly the same as a load range C with higher PSI. Toyota's recommendation only takes tire size into account, not load range, construction, design, etc. So it's merely a recommendation, a place to start.
The more common
requirement that pressure is based off of is the tire. Most tires only have a max pressure, though many have a minimum as well. To go back to my truck as an example, I'm running 37x12.5x16.5 Goodyear Baja's, and they recommend "at 3850 lbs 50 PSI when cold." Notice that the tire pressure is based off weight? Now none of our pigs are
that heavy, to the point where they'd be hitting 3850 lbs per tire (yikes!
), but based on the tire manufacturers testing 50 PSI is ideal at 3850 lbs. So while the tire would happily run 50 PSI, you would only enjoy it if you were looking to loose some teeth while driving down the road.
For most tires, the max pressure they'll happily run at is far higher than what we find comfortable, or necessary (based on our weight). So the pressure range often doesn't really apply to us too much. Where it would come into play is running a lighter tire where you might want to run a higher PSI as the weight of the vehicle is bumping up against the max. But for most D/E tires, it's a non-issue. (For example I wouldn't want to run 10 PSI less than max on the
truck. The ride at 70 PSI would suck!)
For my usage, the rim comes into play. Since I'm running the split H1 rim, it's a little different than a one piece. And in this case, the split rim has stamped on it "do not exceed 30 PSI." This is due to the design and construction. Most rims don't have a max PSI (or at least not a max PSI you'll hit), but it's a good idea to look for one.
So to sum up, we have:
Toyota recommendation: 32 PSI
Tire max: 50 PSI at 3850 lbs
Rim max: 30 PSI
So guess what I run? 30 PSI.
For the OP, I suggest you get all the min, max, and recommended ranges, and then make a judgement call from there. But keep in mind that it's heavily based on setup (heavier vehicle requires higher pressure), what exactly you have installed, and how much gas mileage you want to give up for comfort.
