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Discussion Starter #1
Hey guys, I did some searching and couldn't find exactly what I was looking for. Hoping you can help!

I have a 2015 2500 LT Duramax 4x4 crew cab. I put a set of 285/75/17's on my stock 17" wheels. I originally also slightly leveled the front and added Cognito upper control arms. I ended up bringing it back down to stock ride height within a month or two. I had replaced the stock shocks all the way around with Bilstein 5100's about 70k miles ago.

Had the tires rotated and balanced for the first time and they had cupped a bit on the inside edge on the front. They smoothed out a little while in the back, but are not up front again and are cupping further.

I had them road forced when installed, and an alignment from the only shop I trust. Could it be that the shocks need to be replaced? I do tow a 5th wheel about 6-7 times a year, and a little boat the rest of the year. I keep my front pressures between 55-60, and the rears at 65 so the sensors don't go off.

I'm leaning towards shocks as being the issues, what is your thoughts?
 

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Shocks don't support the weight of the vehicle, and don't affect alignment issues. All they are supposed to do is absorb the inconsistencies of the road. Feathering or cupping of tires is due to either alignment or lack of rotation.
 

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See from all my looking it's actually kind of the opposite of what you're saying. from what I've read they would wear on the inside edges for a problem with camber. But copying they said is usually from the bounce that the shock would provide.

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See from all my looking it's actually kind of the opposite of what you're saying. from what I've read they would wear on the inside edges for a problem with camber. But copying they said is usually from the bounce that the shock would provide.

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But shocks should not affect the camber, that is an alignment issue. Camber, caster, and toe are alignment. Bounce/jounce are shock that should be absorbed by the 'shock absorber'

That's what I was taught when I was in school for automotive service. Lots of people have argued lots of different things about this with me and others, but I always go back to what I learned in college for this
 

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Shocks are not the issue. What kind of tires are they? Mud tires are more prone to cupping than all terrains, especially if you tow heavy on a consistent basis. I've always run mud tires on my past trucks, all terrains this time. I just rotate my tires every oil change or every other oil change. The mud tires were usually just starting to cup a little at that point and rotating them constantly helped keep that from happening. My alignments were always set properly but if I left them un-rotated for too long, I'd start seeing the cupping and could really feel it in the rear when I was unloaded.
 

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Shocks are not the issue. What kind of tires are they? Mud tires are more prone to cupping than all terrains, especially if you tow heavy on a consistent basis. I've always run mud tires on my past trucks, all terrains this time. I just rotate my tires every oil change or every other oil change. The mud tires were usually just starting to cup a little at that point and rotating them constantly helped keep that from happening. My alignments were always set properly but if I left them un-rotated for too long, I'd start seeing the cupping and could really feel it in the rear when I was unloaded.

I have Nitro Ridge Grapplers. I thought they would have smoothed out when in the rear, but they didn't. I guess they are what they are and I will just go back to all terrain next time. Love the look, but don't want tht him that the cupping is bringing.

Thanks guys! This is one area of the truck and that I am not good on!
 

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I have Nitro Ridge Grapplers. I thought they would have smoothed out when in the rear, but they didn't. I guess they are what they are and I will just go back to all terrain next time. Love the look, but don't want tht him that the cupping is bringing.

Thanks guys! This is one area of the truck and that I am not good on!


Are you making sure to reverse their direction when you rotate? I always rotated LF to RR and RF to LR. That way the tire spins opposite from what it was doing the last time. That always smoothed out the cupping for me, usually within a couple hundred miles it was totally gone again


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My shop does cross cross them when they go to the rear. Maybe I will start doing it more often than every oil change and see if that helps. When in the rear, would lower it higher pressure back there help to smooth them ou

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There actually is something to shocks and steer tire wear. All the rest of the front end parts can be in very good condition and alignment can be perfect but if your shocks aren't controlling suspension travel, your tires can cup on both sides. Reason being, at the top and bottom of suspension travel, all your alignment settings are different than where it was set in a centered neutral position. Toe probably suffers the most at the limits of suspension travel. Camber suffers as well.

I have a dually with alloy wheels so tire rotation is a PIA for me, or expensive, either way you want to look at it. So I've taken the challenge to optimize my setup to run as long as possible between tire rotations.

Tires are key. MT's won't cut it and A/T's aren't much better. I haul on the highway almost exclusively so H/T's are fine for me. The Bridgestone R500HD has a good solid shoulder that wears very well on an independent front suspension truck like GM. However I was still getting worn edges sooner than I liked, and it was on both sides.

My front end was in good shape so I replaced the OEM shocks with Bilstein 4600's to see if that helped. I was blown away by the difference. The stock crappers were so spongy they basically weren't doing any good. There was nothing wrong with them, they were just horribly insufficient. After I put the Bilsteins on, when I hit really rough uneven areas like bridges, it's pretty much just one bounce and done now. It used to bounce up and down 3-4 times when towing, especially with bumper hitch trailers.

It's been about 25k miles now on a new set of steer tires and I'm seeing virtually no shoulder wear now like I was seeing before the Bilsteins. I know H/T tires aren't for everyone but I'm pretty confident that controlling front suspension travel will help lug tires as well.
 

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With each of the six solid axle 4WD vehicles I have owned there were problems with cupping and the only fix was rotating the tires more often. With a IFS front suspension it can be the front shocks are not doing their job or you have some other part of the front suspension that is in need of repair.

Your tires, front and rear, are underinflated and this is most likely the source of the problem. I run 65 PSI at the front and 80 PSI at the rear. When I first got the truck I ran the front tires at a lower than 65 PSI and after 2,000 miles it was evident from the wear pattern that they needed to be inflated more. When I had a 4000+ lb load in truck and weighed it at a CAT scale, 4000 lbs of the load was supported by the rear tires and only 220 lbs by the front tires. Rotate the tires and use the PSI recommended in the door jamb of the cab and see what happens.

GM recommends greasing the front end in 8 locations every 3,000 miles. I bet I am one of a very small number of Duramax truck owners that do this.

I would not discount problems with the front shocks are with the modification you did there may have been more wheel travel and this will wear out shocks more quickly. With the factory Firestone tires and the Nitto Grappler tires I have had zero issues with uneven tire wear, though I left the front suspension stock and did not screw around with it. I also rotate the tires every 5,000 miles.

With the heavy loads I was carrying the truck's shocks were not working very well. When I added a double leaf set of Supersprings to provide more load support the problems with the shocks went away completely.
 
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