Scalloped Tires
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Cross-Country
Joined: Aug 2019
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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.
Cupping or scallops have many causes, including worn steering parts, worn shocks or lack of following a proper rotation schedule.
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.
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.
I was concerned about over-inflating the tires and affecting the handling and tread life (as ironic as that is). So you're saying I should have been running these at 65 PSI the whole time?
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.
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.
Mountain Pass
Joined: Feb 2021
Posts: 172
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From: Reno, NV
I can confirm that. I got my 2019 at 10,000 miles and the original Michelin on 20 were already scalloped. I changed the shocks and rotate the tires, now at 30,000 they are even…
FTE Leadership Emeritus
Joined: Sep 2000
Posts: 23,174
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From: Stephensville WI
65 PSI might be too much. What you need to do is weigh your truck to find the actual load on the front at rear axle, then find a tire loading chart from the manufacturer. It'll say something like the tire you have will support 2800 lbs at 60 PSI.
A second method is to apply chalk to the tread and roll the truck a few tire revolutions, then look at the chalk pattern left on the tread. Vary the pressure up or down as needed to create a uniform chalk "wear" pattern across the tread.
A second method is to apply chalk to the tread and roll the truck a few tire revolutions, then look at the chalk pattern left on the tread. Vary the pressure up or down as needed to create a uniform chalk "wear" pattern across the tread.
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