Alignment question, advice needed

[Ronmc1954]

I have some cupping going on the outside edge of the pass tire. I rebuilt the front end on my 74 Scout about 7 months ago and had it aligned and it drove great. I notice the cupping and decided to rotate the tires, front to back. When I did that the 74 started driving squirrly, you know the typical wanderer.
Rotated the tires back and it drove fine again.
But my cupping is getting worse, so back to the alignment shop. My question is why would I no be able to rotate the tires, rims? All parts are new and drives fine but the cupping is bad enough that I am starting to feel a washboard vibration when driving slow. Other than that it feels fine, and it tracks good.
Just want to be informed when I talk to the alignment guy on Sat.
Running 31x10.5's
Any thoughts?
Ron

[Thomas]

---Cupping is more commonly caused by bad shocks. Incorrect alignment, due to toe, would be rolling... like as when you over-sharpen one side of a knife blade and the metal rolls over to one side. You can feel the knife blade when you drag your finger or thumb from side to side on the blade (not along), and in one direction it "tickles" or grabs/scrapes your skin and the other direction feels smooth. The direction it feels smooth on is the side that was over-sharpened. Just like the knife's "rolled" steel blade, you can feel the rolled rubber on the tread by placing your fingers in line with the tread (palm down, fingers pointing up usually works best for me), or front to back, and gliding your hand across the tread from side to side. You'll feel the rubber smoother on the side that has been abused... the leading edge... the edge that meets the road first. The tread pattern should be evenly worn. You can discover cupping early by using a tread depth gauge and checking the depth every 2" until you prove or disprove a pattern, but usually only after about 1000 miles will it be noticeable... unless I suppose you have the dough for a quality*, digital depth gauge.

---Sometimes cupping can be from bad ball joints or kingpins, but due to the nature of those parts, due to weight causing negative camber, wear would be more commonly found on the inside of the tire. What happens with cupping is; The shock keeps the spring from flexing out of control. If it fails this task, the suspension bounces. When this happens at an extreme, the tire will momentarily leave the ground. When it contacts the ground again, it shaves off a portion of the tread. It then gets a hopping rhythm from the domino effect caused by hitting that first cup, then it grows to three cups, then four, and so on, and so on, and... and cuts out a section every 4" or so. Not noticeable by eye until about 3000 miles or better (about 10,000 miles on a transport truck). This is why a good serviceman will try and sell you new shocks when you buy new tires. Documented: New shocks will prolong the life of a tire by 60%.

-OT... somewhat,

---Centra-Matics do work for balancing... as well as to help correct cupping; But the tire that is cupped has already been hammered on. They also prolong the life of a tire by another 30% or better. No BS, no hype, no commission, just a fact. for transport trucks they run about $150-$180 a pair now and around the same price for a full set for Passenger & Small Truck. They also have been installed behind Interco's SS TSLs on a balancer and no weight was needed... where someone would have spent 20 minutes adding damaging weights to a rim in at least 3 spots and still not zeroing the tire out. There's a chart here that shows how much pounding force is applied to a tire with weights per speed. Safety & savings might get you to consider purchasing a set next time you put out $,$$$ for tires & rims... and saving the wheel weights for reloading.

[Comanche Scott]

Hi Ron,

What all was rebuilt on the front end?
The issue with cupping, is that it can come from a lot of places. Here is the more common items:

• wheel bearings
• knuckles
• shocks
• wrong tire pressure
• mis-matched tires
• out of true rims
• out of true tires
• worn spring/shackle bushings
• too long shackles
• too tight shackles
• too loose shackles
• crabbing
• incorrectly set toe
• worn springs
• incorrectly torqued u-bolts
• bent axle housing

There is more, but it get's more esoteric and harder to check in the garage.
So while the simple answer would be the toe was set incorrectly, it could be a combination of things.
I'd recommend knocking off as much of this list as possible before going in on Saturday, if you can.

Also the shop should ensure the Pitman arm is locked straight first, then adjust toe. Then remove and re-center the steering wheel if needed. This eliminates the effect of any Ackerman that may come in to play from an offset Pitman arm. Sometimes shops use the steering wheel for a centering point, instead of the Pitman arm (after all, who removes a steering wheel anymore ). So watch, and ask about that. While at it, have them check/set the steer stops (if adjustable with your axle). That is something else commonly missed (not so much for cupping, but for axle joint life and turning radius).
Hth,

[Ronmc1954]

Thanks for the info Thomas, in response the shocks are Bilstens less than a year old all wheel bearing,ball joints and tierod ends are also less than a year old. But in my mind I should be able to rotate tires without any issue.
The only thing that might have cause a problem was the last time I was in the Rockies I did smack a rock pretty hard on the pass side, it hit hard steel not rubber. It drove fine after that, but it is the only thing I can think of that might have cause the cupping. I would be happy having it aligned and rotating the tires. There is still good tread on all four.
Thanks
Ron

[Greg R]

I was in the Rockies I did smack a rock pretty hard on the pass side, it hit hard steel not rubber. I

Being that it's only one tire, my WAG(wild assed guess) is that a tie rod or steering arm is bent making just that one tire toe to much while the other is still in spec.

With "new" rubber on that side when you rotated them, you'd notice the L&R are fighting for track and you'd get the wander.

Have the shop put that tire on a spin balancer and check it for runout, I've had a rim or two knocked out from smacking a rock.

Let us know what the shop says!

[lightningflash]

Thomas,

Those Centramatics things are very cool. I suppose on a vehicle that you plan on keeping for a long time the price would be offset by multiple sets of tires and re-balancing. I might have to consider some of those in the future.

[Ronmc1954]

Thanks for all the info guys! Greg I would have to agree with you, but the damage sure is not visible. The rock I hit was in front of where I was parked, I accelerated about 2 feet and bang it hit something like a rock no pun intended. I guess I am saying that because it did not hit rubber it felt like the frame. So I don't think the rims are damaged and the tires did balance before.
It will be interesting to see what they find.
Thanks again
Ron

[Thomas]

Originally Posted by Comanche Scott

... The issue with cupping, is that it can come from a lot of places...

---Kinda like an alignment pro saying the camber & toe need to be adjusted when you throw the caster off lifting a Scout, rather than knowing the caster needs to be corrected , while one or more components can be bad, causing many different wear areas or patterns, "cupping" on the outside of the tire comes from one place primarily, and that is damaged shocks.

---There's outside, center and inside on the section of tread. Discussion was about outside tread.

---Over-inflation or correctly inflated tires on too narrow a rim, would cause uneven wear on the center tread, so no cupping would be on the outside or inside tread.

---Under-inflation or correctly inflated tires on too wide a rim, would wear the outside & inside tread, so if cupping is on the "side" treads, that would mean the tire isn't bouncing for one, it's absorbing the shock, so no cupping at all.

---As I described, the wear term "cupping" is because of the spring not being controlled and causing the tire to hop after the uncontrolled spring rebounds from a bump in the road. When the tire returns to the ground it gets material torn from it. The next revolution finds that ramp and hops again and again and again and quickly the wear pattern has been made. One cup leads to two, two to three, three to four, etc., until it goes completely around the circumference. "Feathering" as I referred to as "rolling", is from incorrect toe. The direction of the feathering/rolling of the tread shows which it is, toe in or toe out.

---Wobbling would cause uneven, diagonal wear across the tread. Bearings would then be suspect.

---Calling wear on every other lug of an MT tire "cupping" would be wrong unless the shocks were bad. They're made to dig and some aren't even made for highway use. Kinda like an Ag tire wearing in the center might not be from over-inflation... if it was driven on pavement. That's abnormal wear due to wrong application, not "cupping".

-Ron,

---My apologies for not completing the explanation of the relationship, where new shocks should be suggested during a purchase of tires. Once a tire begins "cupping" (the term you used that defines wear caused primarily* by bad shocks) & some people still call it "dishing", it cannot be corrected. It's being out of round in a pattern... multiple areas almost identical in spacing, all around the outside circumference of the tire `will almost be there for the life of the tire once the pattern is deeply worn. Kinda like scar tissue.

---The wear is nearly irreversible once it is "visible"; After say 3000 miles. So, if the old shocks' damage was "near visible", the wear will appear on those tires about 3000 miles after new shocks are installed. Irreversible if it is deep scar tissue unless you want to pay the $$$ for truing a tire, which would be a bad idea where tires need to be the same diameter... like 4WD dually application, or right & left sides.

[Comanche Scott]

Originally Posted by Thomas

---Kinda like an alignment pro saying the camber & toe need to be adjusted when you throw the caster off lifting a Scout, rather than knowing the caster needs to be corrected , while one or more components can be bad, causing many different wear areas or patterns, "cupping" on the outside of the tire comes from one place primarily, and that is damaged shocks.

Er... no, the information I posted is based on real world testing, experience and engineering.
Sorry dude, but you've assumed incorrectly on this.

Scott

[lightningflash]

At the risk of asking a stupid question, somebody in one of the threads said something to the fact that since the front of a Scout has a straight axle and the caster is not adjustable, the only thing you can adjust is your toe....but what about the camber?
Is the camber not adjustable on a Scout?