Tires: Bulging, pot holes, tire wall

Question
QUESTION: Hello Barry,

I purchased brand new Dunlops P60 from TireRack in Apr 2008 when the odometer was 120K, and I found out today that one of the tires (front driver's side) has a bulge on the tire wall, near the air valve. The bulge is like 1/2 inch wide, not too bulky. It runs from near the point where the air valve inserts in the tire, following the radius towards the center of the tire. The tires have been ran only 10K miles, and this car is only driven inside the city very carefully, no speeding, no messing. Just to go to work, and back like 8 miles at 30-40 Mph. There's no scratches on the tire, its wall, the rhim, or the wheel cover, so I don't think this was caused by impact, a curb or anything like that.

Is it dangerous to drive with the tire like that?

Would it help stop the progression of the bulging if instead of 32 psi of air I get it down to 30?

Thanks in advance,

Richard

ANSWER: Richard,

I'm going to disagree.  I think this was caused by an impact - the tire bottomed out internally.

Yes, I think this is dangerous and you should replace the tire.  Eventually, it will blow out and you do not want to be driving at high speeds when that happens.

---------- FOLLOW-UP ----------

QUESTION: Hi Barry,

But isn't the tire supposed to be designed for the road? Honestly, I drive very carefully, and I don't remember hitting anything. How can the cause be determined?

Thank you in adavance

Answer
Richard,

Even the best constructed tires have situations where the road can damage it - it's just a matter of degree. Certain shapes of pot holes or hitting something at particular angles can put unusually high stresses on the tire.

How to determine?  Well, it takes an expert, but I can tell you this much.  Bulges that would be caused by manufacturing processes show up as soon as they are inflated for the first time.  Anything else can reasonably assumed to be impact damage.

But circumferential splits on the inside is a sure thing.  Other signs can be more subtle and require someone who has experience in analyzing failed tires - which you will not find at the corner tire shop.