Tires: When to replace?, performance parameters, tread depth

Question
Hi Barry, what's a practical way to know when tires need to be replaced?

Thank you in advance,

Rick

Answer
Rick,

There are a number of things to consider when deciding when to replace your tires - state of wear, tire age, and, well, let's call it other.

State of wear - The legal limit is 2/32nds of an inch tread depth remaining.  At this point, a bar should appear across the face of the tread.  However, as a tire wears, some of its performance parameters will deteriorate - like hydroplaning resistance.  For this reason, I recommend that tires be replaced when they reach 4/32nds of an inch.

Of course, this assumes the tire is evenly worn.  If the tire is not evenly worn, then the tread shoulders could be completely worn out, with plenty of tread in the center - so this has to be taken into account.

Tire age - The latest research I have seen says that tires deteriorate with age regardless of how much they have been used.  My current recommendation is to remove tires when they reach 10 years after the date of manufacture - 6 years if you live in the following states - CA, AZ, NV, NM, and FL - and proportionally in between the further north you go.  For example, TN would be 8 years.

Other - There are a few items that should trigger tire removals:

A vibration that wasn't there and gradually gets worse, could be a tire separating, but it could also be the tire developing irregular wear.  Rotating the tire might help the irregular wear, but if the vibration continues to get worse, then the tire is likely separating.  As a gauge, a tire that is separating will go from unnoticeable to blowout in a couple of hundred miles, where irregular wear will take 1,000 miles to get noticeably worse.

Cracks, cuts:  Tires will naturally develop small cracks over time, however a distinct crack might be an indication of something else.  Obviously anything deep, especially where the casing materials are exposed should trigger a trip to the tire dealer for his inspection.

While I can't think of anything else, I'm sure there are a few things I have missed.  If I think of some more, I'll do a followup.

Hope this helps.