Yes 30 PSI is too low. It's for grandpa's and grandma's. Jack it up to 42 PSI both front and back. Your tires should be rated at upto 44 PSI if I'm not mistaken. So check the max allowed PSI on the tires first. Most are 44 PSI.
Yes it will help fuel economy as the rolling resistance on the tires have reduced tremendously.
He's got plenty rooms. Jack it up 10 PSI or so.
cheez
If it's just 5 PSI, it'll hold OK, and you'll get better gas milage. However your savings may be eaten up by early center wear on your tires.
Unlikely to happen but if it does happen, op can always reduce the pressure next time. My friend's car had the pressure at like 60psi, way way too high on the rear tires of his car. He regularly inflated his tires at the gas station and I guess pressure gauge wasn't too accurate so when it came time to replace his tires, he found that the rear did wear unevenly but it was only like a difference of 2/32" which is a lot less than you'd expect with such a huge pressure difference between what the manufacturer recommends (his car 30psi) and what they were.
For me personally I keep a lot more pressure in the front tires than the rear as I drive in hilly areas and my tires wear down the sides a lot if I don't keep them up. If you find the car rides unsatisfactorily you can always reduce the pressure but I think you'll find you like the extra pressure compared to what the factory recommends.
I run 34psi on my Eagle F1 Supercar tires and I just noticed last week that there is significant center wear on my treads. New tires for me next summer.
I run 34psi on my Eagle F1 Supercar tires and I just noticed last week that there is significant center wear on my treads. New tires for me next summer.
What size tires? What car?
Ugh. Those are awful tires. Replace them asap anyway!!!
Let the chalk tell you
You can also “calculate” your tire pressure with the chalk method. This involves coloring a section of your tire with chalk to see how much tread is making contact with the ground. Start by finding a flat road surface. Concrete is actually the best choice, but you can also do this on asphalt. Make a mark with soft chalk that goes all the way across your tread. Then, gradually drive your truck forward about 50 feet and then backwards 50 feet.
Analyze the chalk on the tire. If the chalk is only worn off on the center of the tire, reduce the tire pressure slightly and go through the process again. With the adjustment, you should see the chalk wear off more broadly. Keep making tiny adjustments in the tire pressure until the chalk wears off evenly and all the way across the tread.
You will have to complete this process for each of your four tires. Once you’ve found the right street pressure, add 10% to all four tires. Then, measure the tires and add pressure to balance them. As explained above, you need to measure from the wheel to the ground. Start by balancing the profiles of the front tires with each other. Then, balance the front tires again with the rear tires. Always adjust the tires with the smaller profiles by adding air.
The advantages and disadvantages of this method are the same as those involved in the second method above. If you go through the process correctly, you end up with the ideal tire pressure. But, this method is tedious and there’s a reasonable chance that you will make a mistake.
285/40/18 in the back and 255/45/18 in the front
Yeah those are really huge tires so if you've got a light weight car, I could see that happening. On more narrow tires, like say 215mm I've never had the tires wear unevenly from more pressure. Then again a 215mm wide tire on a 3500lb vehicle is likely similar to a 185mm wide tire on a 2400lb car, again another car I've never see wear unevenly. Larger tires unless specified as Low Load (vs. standard/extra load) have more load carrying capacity so with more pressure might have a higher tendency to wear in the center with more air...
But yeah as everybody has said, those are shitty tires.
The highlighted bit is very simple. If the OP is running the same tire that the engineers designed the car with this will be the pressure to expect the best all round performance of the car. The tire may be rated higher as it is designed to be used on more than one vehicle, check the tire manufacturers listings to see if it is meant to be used on your car.Remember Door Jam PSI is for the stock tires. For Ex: Pressure inside the tires affects load rating and its speed rating. So it can be different vs stock.
You should be able to run 35psi without issue imo.