Cupping - rears ???

[Mark Rinker]

If it wasn't so obvious, I wouldn't believe it. Brand new set of Michelins, and they are cupping - on the rear axle, at center tread. :confused:

Also noticed while traveling with empty trailer this weekend, that I get ocillating motion easily on cement roads with seams. Had to slow down a couple times to stop the "...whop whop whOP WHOP WHOP!" that was nearly bouncing my wife out of her seat, making it impossible for her to type on her laptop...

What gives? All new tires and shocks. I'll shoot a pic of the tread wear and post it, soon.

[rogers]

Could be badly balanced tires or maybe you lost a wheel weight or two. The tires could also have significant "run out". You might want to get them "road force" balanced. Could be you got hold of a bad batch of shocks. That seems less likely though. My guess would be tires and/or balance.

[Mark Rinker]

Shocks are new Bilsteins, I am going to rotate/balance first. If it continues, I'll pull the rear shocks and check them.

[MacDR50]

Mark; are the wheels stock? If they are loose on the hub then a lug-centric balance may give you better results. I was told once that the little blue spot on the sidewall of new tires indicates the best mounting position. The spot is supposed to be aligned with the valve stem. I can't vouch for this so would be interested if anyone knows whether this is true.

Answered my own question with a bit of research.

http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=17

[Mark Rinker]

Stock 3500 series steelies. All four were balanced on installation of new 285 Michelins, only about 7K miles ago.

Put on 400 empty miles with the transport trailer today, mostly across WI-29. Occilation was terrible on seamed cement stretches. Anywhere new asphault, smooth as silk.

Have a boat on now so no issue for a few days until unloaded in RI.

More soon...

[bobt]

I had the ocillating motion and the whop whop whop problem back in '93 in my new ext-cab dually/w camper on interstate 90 in Minnesota and eastern South Dakota. I'm sure that on that occasion it was simply the relationship between that wheelbase and the distance between expansion joints in the concrete. Also, those particular concrete slabs didn't seem to be perfectly flat. I think that's why the bounce got progressively worse. Like you, when I got away from that particular stretch of concrete, it was fine. Don't recall ever running into that problem anywhere else.
Bob

[Mark Rinker]

I'd go with that, Bob - but it does not explain the cupping of a brand new set of $1100 tires.

I've run at least 8 sets of Michelins over the years, and never seen anything like it.

[DaveBr]

You may possibly need a four wheel alginment. Was this ever done to your truck? Check U - bolts to see if they loosened off.

[Mark Rinker]

I am now thinking there are two separate things going on here...

Empty trailer is simply a problem on certain concrete/seamed roads. Its a function of axle spacing and undampened, unsprung trailer weight.
The center cupping has been caused by heavy towing use - combined with new, tall tread blocks that are 'folding over' under acceleration and braking.My theory for now...will see what happens after the next rotation. I am also considering the four wheel alignment. U-bolts are fine.


Thanks for all the good input.

[cowboywildbill]

My front stock Generals cupped, just in the middle. They seem to be balanced fine and aren't scuffing or wearing uneven. It looks like the caster and camber and toe are all OK.
I put on new shocks and moved them to the rear. Thay only have about 12,000 miles on them. I have 17,000 on the truck the cupped tires were two that I had from my other truck and hadn't been run much. They were from our 06 Chevy.

[Mark Rinker]

Update after rotation and ~10K miles. Cupping at rear hasn't returned, empty ride was improved with adjusting hitch height. (New trailer's rearward axle placement is to blame for tendancy to occillate more when unloaded, on seamed concrete roads like WI-29.)

I believe the moderate cupping on rears diring first 10K mile breakin was in fact due to tall center tread blocks 'folding over' at under aggressive loaded trailer acceleration. As tread blocks are reduced, cupping in rear has (nearly) disappeared.