33x12.50 R15 On 15 X 7 Stock Rim - Tire Pressure Question

I am curious to learn from others that are running 33 x 12.50 on stock 15x7 rims: what street tire pressure are you running to get your contact patch flat for even tread wear? I know it depends on which tire, weight of vehicle, but I am curious to see what everyone else is running.

I recently installed General Grabber ATX tires, load range C2, max PSI of 35 and load index 108.

Per load index chart at Discount Tire Direct: My tire carries 2205 pounds @ 35 PSI. Multiply by 4 tires = 8,820 total vehicle weight if inflated to 35 PSI.

https://www.discounttire.com/learn/load-range-load-index

Curb weight of 2004 Nissan Xterra is 4,075 pounds. Gross weight (maximum loaded weight per owners manual) is 5,200 pounds. I have steel rock sliders (~100 lbs), front bumper (~100 lbs) + winch (~80 bs), and rear bumper and tire carrier+high lift jack (~200 lbs). Add a couple of passengers and I am pretty close to the 5200 pound spec.


This means my ~5200 pound Xterra is only using (5200 / 8820) 58% of the load capacity of the tire.

Multiply 35 max PSI by the 58% load ratio, and that equals ~21 PSI, which seems crazy low.

I am currently running at 30 PSI, but I am not making full contact on the outer edges of the tread blocks. Are these large volume tires designed to be run lower than that? I see a lot of jeep guys on forums running in the 26-28 range.

I ran MT's at 32 on the street. Otherwise they bounced around too much. 10-15 on the sand, around 12 off road and 9 on the rocks...

Which MTs did you have? Were they same load index (108) with a max rated pressure of 35?

Did you have stock rims too? I am wondering how your tire wear was. With too high of a pressure and the narrow 15x7 rim, the tread can wear unevenly in the center. Did that happen to you, or did you have wider rims?

Thanks for the data point!

So I had both MTR MK2s (32s) and Duratracs (33s) on my 1st Gen. 15x7 Desert Runners. If I remember correctly, the MTRs chalked flat at 30lbs. The softer Duratracs at 32lbs.

Great info! Thanks. 30 psi has decent contact patch but probably half of the outer most tread blocks aren't making contact. Sounds like 30 is in the ball park from where you guys were running them.

I may drop them to 28 as an experiment and see if that improves it at all, and maybe switch back to 30 if it gets too squirrelly.

As a side note...firestone mounted them for me but gave me about 3 different speeches about how 30 is too low and the tires are too big and I'm taking a safety risk. They had me second guessing my decision with all of their doom and gloom...

But these grabber ATX tires, although a bit floaty, handle 10x better than my 33x10.50 BFG KM2s. The softer tire really does well to absorb bumps in the road.

As a side note: frame rail rubbing on rear axle: anyone running wheel spacers?

And lower control arm rubbing at full lock: just adjusting steering stops? Anything else need attention?

I had the same rubbing issue. Ended up adding 1½" spacers. Made a world of difference.

Good to know. I picked up a set of 1" spacers from:

https://www.motorsport-tech.com/

More expensive, but they are custom machined hub centric spacers that go by the branding of "Bullet Proof Off Road Adapters"...so that had to be good. I just got some for the rear tires, but may add them to the front too.