Hey everyone,

I've got a 2018 XL 6.2L 4x4 with ~30K miles on it. It has Bilstein shocks F/R and I upgraded the front springs to the Snow Plow Package springs after installing a grille guard and a winch. The tires are 315/70-17 General Grabber ATXs on zero offset American Racing wheels. I run the tires at 55 PSI since the max pressure allowed for these tires is 65 PSI. Tires, shocks, springs, wheels, and grille guard/winch were all installed between 10K and 13K miles, since I did it in stages.

The other day I was washing the truck and I noticed a pretty severe and abnormal wear pattern around the inside perimeter and outside perimeter of the tread. The ***** are basically stepped. The wear pattern is identical on both front tires.

So my question is what caused this and how can I prevent it when I replace the tires? I know normally this is caused by an alignment issue or worn out shocks/springs. However, the truck drives straight and the shocks/springs are obviously not worn out. There's a bit of a steering wheel wobble but I figured that was just par for the course with large format AT tires.

The rear tires look totally fine. I've not had a chance to get the tires rotated yet, but they have less than 20K miles on them. The truck has had a pretty easy life and I'm the original owner. I have done some off-roading but nothing that would have damaged anything.

 

How often do you rotate the tires? I've always been under the impression that the inner edges of truck tires gradually scallop even if alignment is good. It's worse with more aggressive tires. The fix is frequent tire rotations for the rear to wear them flat again.

 

They should get more regular rotations. 20k is WAY too long, I rotate my tires every 5k miles when I change the oil. I would expect the cupping you are seeing after 20k in front on any tire.

 

How would rotating the tires prevent abnormal wear patterns like this? That seems more like a bandaid since all you're doing is hiding the problem by moving the tires around. I've owned and been around a lot of cars and trucks throughout my life, and I've never seen or heard of scalloping being caused by not rotating tires.

 

I suippose that's plausible, since this is the first set of "real" A/T tires I've had. It still makes me wonder what would cause it in the first place.

 

The key is to rotate tires BEFORE an odd wear pattern starts. Once a pattern starts it is too late. A few million miles of experience has proven this multiple time over the course of my lifetime. A purely highway tread pattern does better than the A-T also, but we all know that a 4X4 with highway tires will just look funny while we cruise down the boulevard so we put the big grippers on.

 

Abnormal wear on the inside and outside edge of the tire would indicate tire under inflation for the supported load. Are those D rated tires? Most E rated tires have 80 PSI max inflation ratings.

Cupping or scallops have many causes, including worn steering parts, worn shocks or lack of following a proper rotation schedule.

 

Install a good steering stabilizer and caster shims (probably needed). Also check your balljoints and check for slack in anything as general maintenance.

You will need to rotate every 5-7k miles especially with knobby tires. If not you will get that wear pattern and it will exasperate to what you have now.

After owning a few of these and other solid axle makes thats the deal. You may want to rotate and run them on the rear and try to get 7k more miles out of them.

 

Quoting this one because it is most likely correct, and because I know a bit about the Grabber ATx's (been using them since the AT2's).

Depending on the size of the tire, these could be D or E rated tires - and I would strongly suggest when you get new tires to get the E rated ones. You're putting them on a Super Duty with a likely GVW of 10k lbs, AND the E rated ones give you a stiffer sidewall to begin with that actually helps fight this cupping when you are aired down.

Having had MULTIPLE sets of Grabber AT2's and ATx's, if you want to get good wear and not rotate them every 5k miles, you need to run higher pressure in them. They are an AT tire with a soft tread compound, so they wear quicker when they're aired down because (especially with D rated tires) the sidewalls can flex more, particularly in cornering. I have found that running the D-rated tires on a Super Duty basically requires them to be run at 65 psi cold to get good tread wear, and rotate them roughly every 6-9k miles. I've put upwards of 60k miles on sets doing this.

If you get E-rated tires with an 80PSI rating, I still recommend staying in the 60-65PSI range for good tire wear and better fuel mileage, and rotate the same 6-9k miles to keep the wear even. The last set of E-range tires I put on a truck I ran like this, and got over 70k miles before I traded the truck in. The tires still had a long way to go before needing to be replaced, too.

Long story short, if you want to run 50PSI in these tires you need to be rotating them OFTEN, likely 5k miles or less. They're a very soft tire compared to other AT tires, but a good maintenance schedule and proper inflation will make them last a long time. 20k miles between rotations is too long for ANY AT tire.

 

20k without being rotated... there's your answer. They should have rotated 3 or 4 times within that period.

 

I dont think he needs an E with the light weight gas motor as long as he isn’t using the truck for heavy loads often.

But with D tires you really have to get your air pressure right. E is a lot easier to deal with.

Back in the day before all the 18 and 20 inch tire options if you upsized there were not a lot of E options. Have a little experience with this.

 

Throw the cupped wheels on the back and they will flatten out for you

 

Powerbrake

 

Yeah that will do it in a hurry, hammer down now...

 

Agreed. I hope I didn't come off as slamming the OP for potentially running D rated tires. Many D rated truck tires support loads in excess of 3600 lbs per tire, but as you stated, the tire pressure has to be correct.