Tire cupping

[garybo]

I have a 14000 lb camper with this tire history:
June 2011 at 105,243 mi, got new tires: Cooper Discovery ST MAXX, LT 235/85R16 E1
tire pressure for weight: 70psi front, 60psi duals
June 2012 at 114,778 mi, rotate the 2 unused spares to front, got new springs and std shocks. This was at 12 months and
9,535 mi on the tires. The removed fronts were smooth, evenly worn and tread equal to the duals.
Nov 2011, new wheel bearings and seals.
Oct 2012 at 128,565 mi, the front tires were making a huge noise at under 10mph, ALL tire lugs were severely "cupped",
ie, each lug had two areas: one half high and one half low in a random pattern; the tires were evenly worn but all lugs
were as described; front tread was 13mm, duals tread was 12mm, so seemingly the tread wear front and back was about equal, except for the severe cupping on front. Alignment was perfect, spring U bolts were torqued correctly. This was 4 mo and 13,787 mi from prior rotation. We had done no off road and never above 50 mph.
Our owner's manual states to rotate tires q 6000 miles which I didn't follow. The first rotation was at 12 months and
9,535 highway miles. The tires looked great at this time. The second rotation was 4 months and 13,787 miles with
severe cupping. Air pressure was always maintained.
The truck tire shop had no explanation except "tires too aggressive for application", ie, highway use. It's true in
retrospect, we didn't need aggressive tires for good road use.
In the future I'll rotate q 6,000 miles and pay more attention to the tires. However I now have two useless tires unless
they can be shaved? or planed? Don't know about this.
Since all suspension parts measured normal and we didn't put any unusual stress on the tires, and lacking any other
explanation, it looks like the cupping was my fault for not rotating the tires. The cupping result would be from the
difference between putting 9500 miles and 14000 miles on the tires without rotating.
Any other explanation or ideas to prevent this from recurring other than frequent rotation would be appreciated.

 

[FellowTraveler]

Was the pattern saw tooth or just random?

My fronts would get a saw tooth look as viewed from the side which was tracked down to breaking friction on road surface which wears the lugs into a saw tooth pattern on AT or MT tires. Perhaps, breaking is the issue and/or the tire compound may contribute too. Rotate frequently is the only PM I can think of.

 

[1stDeuce]

Hmmm. What does "Alignment was perfect" mean? I just found pretty good cupping on the front tires of my gf's Liberty. I'm the one who did the alignment, and I did lower balljoints after that without checking it again, so I figured it was off. Turns out it was almost exactly where I had set it. (Camber, caster, and toe all right where I set them. All "Green". The toe setting was on the high side, with almost the max amount of toe in though. (I normally do that on trucks with more aggressive tires, which the Liberty has.) I figure the toe had to be causing the scalloping, so I set it to the low end of the spec, and rotated the tires.

I'd start with visiting your alignment sheet. Where in the toe spec are you set? There is some "wiggle room" for a shop to adjust all the settings, so I would think a competent shop could make an adjustment based on your current settings. "Green is good" is not really correct. Some tires are definitely more sensitive than others, and aggressive tires cup much faster than normal tires when the toe settings are not ideal.

Make sure nothing in the front of the truck has loosened up too, like a tie rod end or balljoints. What kind of truck is it anyway??

I have yet to find an alignment setting on my '06GMC that doesn't result in some light cupping if I leave the tires in position too long, but I probably rotate every 7-8k, and that keeps it in check on BFG AT's. It is possible that your STMaxx's might prefer rotations closer to 5000 mi, particularly if you have a chevy/gmc.

Finally, there's nothing wrong with the cupped tires. Rotate them into the rear and they should even back out. If you just can't stand it, I've gone so far as jacking the axle just off the ground with the front tires blocked and letting the tread just touch so it kinda shaves itself on the concrete for tires that were REALLY bad. Obviously there are lots of reasons this isn't a good idea, but it worked for me, just keep the tire speeds really low, like 5-10 mph. You should not see heavy smoke pouring off.

And finally, you might consider dropping the pressure 10psi. It seems like having the pressure too high tends to speed up any cupping that might occur.

Good luck!!
Chris

 

[Hilldweller]

It's always been my experience in fleet management that tire cupping is usually caused by inadequate rebound dampening. (worn or underdamped shocks)

 

[FellowTraveler]

It's always been my experience in fleet management that tire cupping is usually caused by inadequate rebound dampening. (worn or underdamped shocks)

I always thought this too about my Burb and tried different shocks/valving and still have the saw tooth pattern on the tires and I have been rotating them more frequently since that was suggested on this forum. I'm now looking into the torsion bars which maybe getting weak so a new or higher load rated set w/keys maybe the fix for me.

 

[garybo]

My stock shocks are new, installed with the springs.
tie rods and ball joints are tight.
These numbers are from the alignment 2 days ago:
On front axle: left toe in range: -.06 to .06, before adj: -.02, after adj .02
right toe in range same; before adj: -.04, after adj .02
"cross camber, caster, SAI": total toe before adj -.06, after adj .04
I guess these toe numbers move the tires from diverging (-) to converging (+)? time will tell if this is better?
I'll put the cupped tires on each outer rear location to see how they even out.
Steering and braking tracks straight.
thanks,

 

[BillTex]

A 14000 # camper?

Dude...you need more tires or a smaller camper...

 

[bat]

The old Fords were pretty bad about cupping until you put a set double shocks up front. Did you say what type of vehicle and year if I missed it sorry.

 

[garybo]

I have a 14000 lb rig- a Fuso FG with a box camper on the cutaway.

 

[BillTex]

So your truck+camper= 14k #...that makes more sense!

A 14k# camper...yikes!

Anyway, cupping is often an indicator of belt shifting...could be caused by several factors; too high sidewall, over loading, age,...

Bill

 

[FellowTraveler]

I like over kill when it comes to tires and would look into higher capacity tires for that heavy rigs next set when the time arrives.

 

[1stDeuce]

Given the alignment "before" readings, I think you may have fixed it. It was toed out, granted not by much, but with non-highway tread tires, enough that you could get some funky wear patterns. They put it right where I would have, which is just slightly toed in. Keep an eye on it, but I think you'll have much better luck this way.

C

 

[garybo]

I'll watch the progress. Putting the cupped tires on the outside rears. We'll see how things go. Gary

 

[Dale]

My F250 7.3L with Goodyear Silent Armor 235/85R16 cupped on the outside edge,as did the Coopers that came with the truck. I replaced balljoints and shocks (Bilsteins 5100's and it was corrected. Hope you get it worked out.

 

[garybo]

Just to expand, we first took the rig to a truck tire store to brainstorm about the cupped tires. Decided to get the alignment and put the cupped ones up as spares. Unknown was that one wheel nut seat on a cupped tire wheel was damaged, then the shop tried to take off this nut not realizing it was left handed. They spun the nut irreversibly into the damaged seat and had to torch off the nut and lug. Then off to the Fuso shop to have the lug replaced, then get a new wheel to replace the damaged one. Total one week. Ah, life on the road!