Front tire cupping

[artvonne]

  Interesting how they claim dog tracking has an effect on wear or cupping, ive never actually read that before, but had surmised it.

  I learned wheel alignment in school, and did it professionally for about a year when I was 20. I was always getting beef for taking too long, but I was just trying to get them right and right takes longer.

  The goal of the rack, at least around cars, is to sell steering parts and labor, often times parts and labor that arent even needed. The alignment is just a come on to get you in the door. The place I worked even sent me to a class put on by MOOG on how to sell more parts, how to convince a customer the parts are shot when in reality they had only slight wear, or no real wear at all. I think I quit that week, I just wasn't the criminal type they wanted working in that bay.

  I havnt had a vehicle on a rack in over 15 years, I figured out how to do it myself with string and eyeball, I even made my own trammel gauge. Its not rocket science, its really just 4th grade geometry, and all the angles can be found with the same simple technology the Egyptians built the Pyramids with. 

[akroyaleagle]

I had this problem through three sets of Michelin tires.

I changed the shocks and went to different tires and haven't experienced it since.

[gus]

Funny thing about front end alignment on autos and pickups. You can get one done and take it to another shop and they will readjust it!!

This seemingly can go on forever until you run out of shops!!

[TomC]

The R250 is a regional tire-meaning it does not have the decoupler grove on the edge like is on the R299 to prevent the cupping on the edges.  If you're getting cupping on just the right side, you may have to much positive camber on the right side.  Usually you should set the tires at zero camber on the left with a bit negative on the right to combat road crown.  Then set the toe to 1/16-1/8" in.  Caster should be set at whatever your factory says-and it is drastically different if you have manual or hydraulic power steering.
Next set of tires-buy steering tires for the front and the R250's in the rear is alright.
Some even run the new tires for a few thousand miles on the rear to get them tracking straight-then mount them on the front. Good Luck, TomC

[JohnVickrey]

Thanks everyone for all you input
I may be on to something.  It seems the left rear is riding higher than the right by a couple of inches.  Seems that would mess with the camber on the right front. 

I going to reset ride height today and we will make a 450 mile run back to FL.  If it's gonna cup I may be able to see it after 450 miles.

More news later.

[bevans6]

Having the left rear up too high will transfer weight diagonally to the right front, so that is a good thing to adjust.  Camber is built into the axle, it's not particularly adjustable on a solid axle setup.  Neither is castor on my bus, without huge fuss.  Checking will let you know exactly what you have under you, and take it from there.  I think the tire issue pointed out by TomC is a real good catch!

Brian

[artvonne]

  On a straight axle, camber is built into the axle during the stamping/forging. If there is more caster to one side, they put some twist into it. To add or subtract caster you wedge the axle forward or back on the spring seats/bunks. Many shops have hydraulic equipment to bend the axle to alter camber, but I dont believe that is allowed on heavy trucks.

  With the front air ride interconnected right to left and right to left lean controlled at the rear axle, as on most Buses, a right lean should not put any more weight onto the right front. Unless its grossly leaned over, I am having difficulty seeing how that would cause the issue. I guess its possible im just not seeing it.

[TomC]

AV is correct in that even a leaning bus will not change the tire suspension geometry in the front.  Trucks/buses still can have the axle bent to correct for a camber problem.  I found from my first truck, if the camber is off (like mine was negative [bottom of the tire in, top of tire out]) bending the axle will fix it-but it has to be done about 4 times before the axle will remain in the new position (high tensil steel).  Good Luck, TomC

[artvonne]

  Tom, the trick is to over bend it, lol, go past the point you wanted.

  This old aircraft mechanic once explained how metal has memory, it wants to retain its original shape. This plane crashed and bent the prop. Dial indicator showed crankshaft prop flange runout was something like .003", about .001 out of tolerance IIRC, which would have automatically made it a $3 piece of scrap iron instead of the $15,000 crankshaft he wanted it to be. So he walloped it with a big leather faced mallet once or twice..ring ring, dang if it wasn't .0005 out of true and $14,997 more valuable. Sorta. That old man was crazy but he sure taught me a lot. He sent it out for crack testing and X-Ray and it came back clean.

  Makes you wonder just whats flying around up there eh? I told my Dad about that and he just shook his head. He said if anyone really knew the crap they were flying in WW2 they would be amazed, it was pretty much flying junk. Only thing that saved us was our junk was less junky than their junk, or we had more than they did. We probably wouldnt have had anything to fly if they had X-ray testing back then, lol.

   

[stevet903]

Here's a link to show how they bend the axle to correct the alignment - It's some stout looking equipment!!

http://www.beeline-co.com/PDFs/Truck_Axle_Correction.pdf

[chev49]

That's kinda how you do it yourself...only it doesn't cost like that thing.

[JohnVickrey]

Well, I have about 500 miles on the tire since moving a rear to the front and adjusting ride height.  No noticable signs of cupping yet

[artvonne]

Here's a link to show how they bend the axle to correct the alignment - It's some stout looking equipment!!

  I never worked with anything that heavy, our equipment would only work on trucks up to 1 ton. But it was real heavy stuff to lift and move around, that what you posted is much heavier.

[white-eagle]

Well, I have about 500 miles on the tire since moving a rear to the front and adjusting ride height.  No noticable signs of cupping yet

Where did Lois sit on the way back?  Just asking.  No Lois, i didn't mean anything by it.  Really. 

Glad you may have discovered the fix.   Better than replacing rubber every 1000mi.

[rv_safetyman]

My cupping was the result of too much clearance in the front bearings.  Set them correctly after new tires and all seems well.

I monitor a lot of RV S&S forums and there seems to be a strong theme that Goodyear tires (not sure of the series) have cupping problems.  It has come up a ton of times and the results are always the same.  Replace the Goodyears without changing anything and the problem goes away.  No first hand experience, just reporting what is being said.

Jim