This topic concerns a potential SAFETY issue so is a bit more involved as it is important that everyone understands the situation.
I have 5 1/2-year-old 12R Michelin XZE tires on our coach. No cracking, and have performed well.
I found sidewall 'bumps' (Tire Center gent, said they're not
'bulges', as they're so slight). One maybe 3/32" of a protrusion, the
other much less. The gent said they could be belts that are
misplaced or broken. But he also said the XZE's have a thicker
sidewall, and that the outer layer of the tire could have separated.
I know it's hard to give advice based upon a description, but I wanted
to ask your thoughts on the opinion given to me by this tire gent.
He suggested that I monitor the size of the 'bumps' daily, and if they
don't grow, he felt that they were safe to drive on. He commented that the tire was so overrated for what it was
carrying weight-wise on my RV, that it was not working hard.
I've always thought that once a tire starts to break down, it was at risk for a catastrophic failure?
The tire was not unmounted for inspection, but if it was an outer layer
separation, as he said it could be, how would they be able to see this?
Opinion? At 5 1/2 years of age, is it worth even considering monitoring and watching for growth? Or just replace and move on?
Here is my reply:
First off, I do not feel that sidewall "bumps," "bulges" or "protrusions"
occur because of misplaced or broken belts. Belts are under the tread
not on the sidewall so I have to wonder what training, if any, the
"gent" at the tire store has received on tire construction or inspection
procedures. Also not sure what he is talking about as the "outer layer"
of the sidewall. In a truck tire there is basically the thin innerliner (a bit like having a tube as part of the tire),
then body ply, then the sidewall. So, if he thinks the sidewall has
separated, then the tire has failed and should be replaced.
Now, some fact-based observations on sidewall bulges or outward
protrusion vs. depressions that are inward toward the air chamber and are
indications of two completely different causes.
The inward depressions can occur once or twice around almost any radial
tire. If you take a close look in full sunlight of smooth sidewall tires
you will see depressions that might be about 1/16" deep and 1/4" to 1/2" wide in the circumferential direction. These are caused by the lap splice of body
ply material that provides more resistance to the slight growth seen in
all radials due to inflation. These depressions will run a radial
direction from the wheel to the tread and seem to disappear as you get
near the tread or near the wheel. These are normal and I would only
consider them minor cosmetic features of a tire.
An outward bulge may be 1/2" or as large as a couple of inches in the circumferential direction. The larger or more distinct, the more
concerned I would be about the durability of the tire. Usually bulges
are the result of some impact damage done to the body cords that
resulted in a few being broken due to shock loading.
Here is a blog post I did with pictures of bulges and depressions to help people understand.
Here is a post on an Impact Failure I had on my personal car.
Now on some with small features, the eye plays tricks as to it being a bulge
out or a depression in. I have even seen instances of two depressions
being close together such that the normal sidewall between the
depressions gave the appearance of being a depression. The simple tool
to use is a ruler or straight edge and to lay it across the area of
interest. This will quickly identify if you have a bulge or depression.
What to do:
Review my blog posts above.
You might also find a different dealer. A simple Google for "Truck Tire
Dealer Town" where "Town" is a nearby larger community, should give you a
number of options. For 19.5
and larger size tires I would only deal with a Heavy truck Center.
You might also contact Michelin at their Customer Contact on
their RV tire page for a suggested location with people sufficiently
trained in tire inspection to pass judgment on your tires.
You can tell them that you're not happy with the inspection you got from
the tire guy as they don't seem to understand the basics of rtuck tire