THANKS TO OUR SPONSOR!

THANKS TO OUR SPONSOR!
Your Ad here
Be sure to sign up for the weekly RV Travel Newsletter, published continuously every Saturday since 2001. NOTE By subscribing to RVTravel you will get info on the newest post on RV Tire Safety too
. Click here.
Huge RV parts & accessories store!
You have never seen so many RV parts and accessories in one place! And, Wow! Check out those low prices! Click to shop or browse!

Wednesday, December 24, 2014

Tire Bulge. Defect? or Damage

Sidewall bulges can be difficult to diagnose. Sometimes it is even possible to misinterpret a depression as a bulge so lets start off today's lesson with clarifying the words.

According to Dictionary.com  bulge means a "rounded projection, bend, or protruding part; protuberance; hump".  I think we can all agree that this is a sidewall bulge.





A depression would be the opposite, or "sunken place or part; an area lower than the surrounding surface". Sometimes I may use the terms "Bulge in" and "bulge out"just to be sure people have a clear understanding.
Look closely at this shot and I think you can see that this is a depression in the sidewall.
 Here are a couple of other shots showing sidewall depressions.






OK So now you are probably asking why are these two conditions in tires and are they defects or what? Lets step back for a moment and consider how tires are made.







The basics apply to all tires, be they small 10" or 12" as seen on micro cars or 22.5 or even large mining tires like this one.






In this post there are some links with videos showing the basic process of wrapping layers of fabric (or sometimes steel cord) that is in a sheet of rubber, around a drum. The place where the builder starts and stops has a "splice". Now the goal is to have a strong enough joint to keep the uncured rubber together till the tire is cured. In some constructions this means a small overlap of one to maybe 4 cords. If the overlap is larger than desired there is a doubling-up of the cord and this is what creates the depression. I know this is counter-intuitive but you need to remember that when a tire is inflated the rubber stretches and the textile cords stretch a slight bit. However if the splice is "heavy" or larger than desired the forces from inflation are resisted by twice the normal amount of cord and rubber so the stretch is less than in the rest of the tire. There is nothing wrong here other than a visual depression.

Now a bulge is just the opposite. If the splice is "open" or there are cords missing then that area will stretch out more as there is only sidewall rubber resisting the air pressure so the sidewall stretches out just like a balloon. A bulge from an open splice is noticeable as soon as the tire is inflated. If you see this on a new tire point it out to the tire dealer right away and confirm the bulge is below the level of concern for that make of tire. This will probably be less than a tenth inch above the surface of the rest of the tire and less than 1/2" wide. If larger I would request a different tire unless the dealer is willing to put in writing that the tire is safe.  Get a nice close picture of the tire for your records and be sure the bulge does not get any larger.

The other thing that can cause a bulge is broken body cord from some sort of impact such as a curb, pothole or from hitting something on the road. Here are a couple shots of a 22.5 that suffered an impact.



.One thing to point out how I know this was not a factory defect. I have yellow arrows pointing to the small amount to irregular tread wear. You will note that this level of wear is fairly uniform around the tire. If the defect had been in the tire from when new I would expect the sidewall bulge to affect the tread wear. Since it didn't, that indicates to me the break of the body cord is recent.

In case you are wondering what broken cord might look like here are a couple shots of broken Polyester cord from a smaller tire.



.I hope everyone now understands the difference between a cosmetic depression and a bulge due to a tire impact.


If you have a Bulge that looks anything like the examples above I would not drive on the tire. If we are talking about a high pressure tire (75 psi or higher) I would not even stand near the tire while waiting for service. A tire explosion can be damaging or even injure people.



Subscribe to the weekly RVtravel.com newsletter or one of our other newsletters about RVing. Great information and advice. Now in our 14th year. Learn more or subscribe

2 comments:

  1. Your article is right on.

    ReplyDelete
  2. Wow i can say that this is another great article as expected of this blog.Bookmarked this site.. link: ExpertPower EXP1233 Battery

    ReplyDelete

Thanks for your comment. We look at each one before posting to keep away the spammers.