Tire pressure questions

I know there are other posts about this topic, but to be frank, they seem crazy. I have a 2016 double cab limited on a 3/1 level and LT 295/70/r18s. The tires are cooper's at3 xlts and I just put them on two weeks ago. The door says 36 PSI which is what I ran the stocks at. After the stocks I ended up with some cooper STT pros, then after that some LT 35x12.5/18 ko2s. I ran the ko2s at numbers like 42-45 PSI and over time realized the centers wore out much faster than the outter tread. I decided to try to do it right this time and did the old chalk test. I started out at 46 PSI which showed obvious wear in the center and no wear on the outter tread. Probably something like 100% center, 0% edge. I went down to 42 PSI and saw about 70%-80% center. After that I went down to 40 PSI and saw around 55% center and 45% edge in the front and noticeable center wear on the rear. I was tired of chalking and hopping in and out of the truck so I settled with about 38 PSI front and 36 PSI in the rear. My issue now is that the front looks pretty underinflated. Is this normal? I know the ko2s have thicker side walls which probably helped to not have this appearance. The coopers just look off. I have seen some posts suggesting 45-50 PSI which seems crazy. Do you all have any real experience with specifically the at3 xlts in 295/70r18? Looking for some answers and opinions. I dont want to have too much wear on the edges and an underinflated look, but I also dont want only center wear to get rid of the look.

 

Cant go by the sticker unless you are running the stock tires detailed on that sticker.

Once you change size or load rating, required pressure could be different.

Use this tool to get you in the ball park. And then if you think you need to you can to a chalk test to confirm based on your actual truck and how you load it.

https://www.youtube.com/watch?v=_T2FfrRHaTU

 

And my guess, based on my experience running 275/70-18s and 285/75-18 (both E load) on a trundra is that pressure should be about 35.

Cant inflate tires based on how they look and be accurate.

 

Exactly what @frichco228 said. There are a bunch of tire pressure calculators available. Then take some painter tape and cover the plate and put the correct pressure on the tape because the common idiot at any tire shop never reads the tire size requirement.

 

Weight at the axle (3200lbs)divided by the max load stated on the tire multiplied by two(4080x2=8160) (since there are two tires on each axle). 3200/8160=.4
Add 20 percent to that number for a safety margin. (.48)
Now multiply that times the max load (air) pressure stated on your tire. (80lbs x .48=38.4lbs)
This number gives you the street pressure for your tire. (38lbs)

 

The easiest way is to simply email Cooper Tire and provide them with your vehicle year and model, stock tire size and inflation pressure, and new tire size. They will respond with the correct inflation pressure.

Second easiest way is to use a tire inflation calculator, but they aren’t perfect.

Third easiest way is to cross reference your stock tire size/pressure to the new tire size/pressure on an inflation table. Toyo tire provides and accurate table on their website.

Personally, I don’t care for the chalk test as anything more than a validation that you are in the ballpark. However, new tire designs do not follow a standard pattern when chalk testing and will skew the results; two tires of the same size and load from different MFG’s will also usually chalk test differently. Also, the chalk test doesn’t account for load and handling characteristics of the vehicle and tire carcass at speed, or various loading scenarios that a pickup or large SUV might see throughout its day/week/serviceable life of the tire - it only judges how a tire contacts the ground at a stand still. At speed, the carcass deforms - even balloons out in the center - and flexes, building heat. If it goes from flat on the ground to ballooned more on the center, the tire is deforming a lot wi try every rotation, building heat and wearing on the tire.

All of this has been accounted for by the tire manufacturer and is condensed in the inflation table. Thus, I would choose option one, two, or three listed above rather than go off the chalk test. As you found out, the chalk test appears to leave your tires under inflated.