Scalloped (cupped) tire wear

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drober23
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Location: Metro Detroit
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Scalloped (cupped) tire wear

Post by drober23 » Wed Jul 09, 2014 1:19 pm

My '75 Westfalia had a "rotation-dependent vibration" that almost completely disappeared when I swapped over to a different pair of tires in the front. The tires I removed had about 20,000 miles on them.

When I inspected the tires that had been removed, I noticed a "scalloping" on both tires. There was not a noticeable difference between the inside and outside. I suspect there is a problem in my front suspension somewhere, but am not sure where to start. All of the stuff up there needs a going-over, but I am looking for ideas as to what might cause.

The interwebs suggest that this problem is due to worn struts or shock absorbers. I have relatively new shocks without a ton of miles on them, so I don't suspect the shocks.

I do occasionally get a "bouncing" effect when driving at highway speed. This seems to happen when there are regularly spaced control joints on a concrete highway. This happened a lot with my old shocks, and still happens sometimes with the new ones.

Anyway, if anyone has ideas, suggestions, or disparaging remarks I'm all ears.
DJ

'75 Westfalia, '79 Deluxe
(plus more busses than sense)

In a time of chimpanzees I was a monkey

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Amskeptic
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Re: Scalloped (cupped) tire wear

Post by Amskeptic » Sat Jul 12, 2014 10:49 am

drober23 wrote: When I inspected the tires that had been removed, I noticed a "scalloping" on both tires. There was not a noticeable difference between the inside and outside. I suspect there is a problem in my front suspension somewhere, but am not sure where to start. All of the stuff up there needs a going-over, but I am looking for ideas as to what might cause. I don't suspect the shocks.
I do occasionally get a "bouncing" effect when driving at highway speed.
Our torsion bar suspension has no boingboingboing spring harmonics, so they are easy on tires even when the suspension is sloppy and worn.

A) Are wheels true? Check all steering components for slop. Do you have noisy ball joint sounds in potholes? Do you have excessive toe-in rasp on the trad blocks? Any camber wear (treads are shallower on one side of the tire than the other)?

B) Wheel balance! Even when the tire shop promises you that the tires balanced up nicely, ask to see the results *before they take off any weights* when you come back in. Never allow a tire shop to clean up a slight imbalance just by adding yet another weight. Two weights (one inside/one outside) per wheel only. No weights over 1.75 maybe 2.0 grams, if they need to use some honking lead anvil weight, ask to dismount the tire and move it 180* on the rim.

C) AFTER you have established correctly balanced wheels, if you have any symptoms of vibration or shimmy, then you can look at the possibility that the high-frequency valving (damping of rotational forces) of the shocks is shot. Running imbalanced wheels can tear up the shocks and you don't even know it. Low frequency valving may still be fine (that is the whole vehicle damping like over railroad track humps)
BobD - 1978 Bus . . . . . . . . . . .111,130 miles
Chloe - 1970 bus . . . . . . . . . . . 206,787 miles
Naranja - 1977 Westfalia . . . . . 93,996 miles
Pluck - 1973 Squareback . . . . . 55,510 miles
Alexus - 1991 Lexus LS400 . . . 72,113 miles

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