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Discussion Starter · #1 · (Edited)
Front tires cupped, pretty badly

Hi All!

I've been running the Wrangler Duratrac's, LT265x75x16's. They are the Load C rated tires (the lower weight carrying version - they also come in a Load E version). 35,000 of driving and I ended up with the front tires horrendously cupped. I've got an '06 Xterra, Off-Road model with the Bilstein shocks/struts. 80,000 miles total on the vehicle.

I'm not certain but I think the cupping may have coincided with my decision to run the tires at 45lbs. of pressure. Why did I do that? Well, I was hoping it would get me better gas mileage. I didn't notice a big difference in that but I figured I'd keep going at that pressure anyway. The rear tires, same pressure, didn't have any uneven wear at all. I've moved them to the front and am replacing the trashed tires with new Duratracs, same tire.

Now I have to decide for sure what caused the cupping. Over-inflation causing the tires to bounce off the road surface and scuff them into the death-cups, over time? But then I have read in more than one place that cupping can be caused by under-inflation. I didn't see anyone note that over-inflation could cause it.

Or have the considerably heavy Duratracs just trashed the shocks in my front struts? I have a hard time believing it's a strut problem because I don't notice the vehicle having any lingering bounciness going on after hitting a bump. How about the entire strut assembly including the shocks? Could the heavier tires just have work both the shocks and springs enough to be the cause of the problem?

Last thing to mention - during this time the right front wheel hub bearing became trashed. It was thousands of miles before I figured out that's what the noise I was hearing was coming from. When I finally figured it out to check the bearing, I could rock the wheel back and forth at the 12 and 6 o'clock position by ~1 inch. BUT, the cupping happened about equally to both front tires, and the left front wheel hub bearing was fine.

I've made an appointment to get the front end wheel alignment checked, but that was before I started researching the possible causes of cupping. Now I'm thinking it doesn't seem like there's any reason to think my alignment is suspect. The vehicle tracks straight, without any apparent hint of pulling to either side. And tugged and pulled on all the suspension parts up front, with the wheels off the ground, and nothing feels loose at all.

I don't want to throw $90 at an alignment check if I can conclude the cupping may just have come from the tire over-inflation. And if it wasn't that, then I still might want to believe it's weak struts/shocks that caused the problem, and not wheel alignment. I think if it was the alignment, I would be able to tell that from wheel pull. Oh, and important to include - I haven't done any mods to the suspension - it's all stock and original.

Thank you, all, for any input you have time to give me! :)

-John Jackson
Amherst, MA
 

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The way cupping occurs is from the tire essentially bouncing. Its similar to the way a whoop de doo or washboard road develops.

The tire CAN bounce from over inflation, and, from the shock valving being incorrect and/or unable to damp the bouncing.

If a suspension of steering component is bent or worn out, etc, it allow play, which can also fail to hold the tire where its supposed to be/allow movement.


A bad shock for example is a LEADING cause of cupping.


If its over inflation alone, typically, the center of the tread is also worn more than the edges.

If a tire edge, inner or outer, is where the cupping is, especially if only on ONE edge, that tends to be alignment and/or a problem with a worn or bent part.

As you know you did have a bad part (hub) for example, that's a likely suspect if the wear pattern supports it. That can also lead to proportionally more stress on other parts left with trying to position the tire without the normal assistance from the bad part(s), and so forth.
 
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