Tires: Tire Repair, proper inflation pressure, underinflated tires

Question
Hi Barry,
Is it safe to just put a plug in a flat tire?  I have read that you should use a inside patch which also plugs the tire from the inside.  A guy who has repaired tires for me says it's a waste of money and plugs are fine.  I haven't had any problems with plugs but am concerned about the safety of using them especially on SUV's.  Also, for an SUV is it a good idea to purchase the next larger size when replacing the factory tire?
George

Answer
George,

Boy!! A bunch of questions:

1)  Plugs are a bad idea.  First let me state this as a principle - repaired tires ought to perform reasonably close to unrepaired tires.  Given that the reason a tire is repaired is because it has a leak - and we all know that underinflated tires can lead to tire failure - that means that repairs need to be on par with new tires when it comes to air retention, etc.  

But plugs are known to leak from time to time.  I'd guess it is 1 in 10.  The usual fix for this is to replace the plug with another, but what gets forgotten is that this consitutes a failure of the plug.  In my book even a 1 in 100 failure is unacceptable.  (BTW when was the last time you heard about a new tire leaking?  We're talking 1 in a million!)

The other thing that is bad about plugs is that you don't know what damage is inside - which is the easiest way to tell how badly damaged the tire is.

Besides none - not a single one - of the tire manufacturers recognizes plugs as an acceptable repair.  That ought to tell you something.

So is it a good idea to go up a size in an SUV?  I think it is a good idea to go up a size or 2 in a regular car!!

Alternatively, I'd recommend you use more inflation pressure than is listed on the placard.

Look for the placard on your vehicle.  The placard, among many things, tells the original tire size and the proper inflation pressure for that size.  The placard is usually located on a doorpost or in the glove box.

I like to use 3 to 5 psi above the placard.  I get better fuel economy, better tire wear, better wet traction, better snow traction, better steering response, better tire durability, and only give up a bit of ride harshness.

“They” say you should check your tire pressures once a month.  Don't trust the guys at the shop to do it.  These guys are paid by the hour and this is one of the easiest things to shortcut.  Besides, there are a lot of mechanics you don't know where to look for the proper inflation.  No, it is not on the sidewall.

Hope this helps.