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Tire Tread Measurements

Can someone explain tire tread measurements?



One mechanic told me that my tire treads are 7/32 and that they're like new. Another said the 7/32 means they're still good but there's wear.



When a tire is brand new, is it 7/32? Or 32/32?



My first pair of tires were bald (so I was told) by the time the car (a Honda Civic '99) was only two years old. I did mostly highway driving back then.



I've had my current pair for 3 1/2 years, still doing a lot of highway driving. 4 months ago I was told they're still like new, though I've put a good 60,000 miles on them. I've driven far less than average these last few months, clean paved roads, and now I'm told I can expect to get maybe another 12,000-15,000 miles out of them.



Not sure what to make of it.
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Comments

  • edited June 2009

    A new tire tread will typically have 10/32 of an inch of tread, and some expensive tires may have 12/32 of an inch. So, 7/32 is pretty good, but is not comparable to a new tire.

    As you have probably surmised, tread wear varies considerably from one model of tire to another, and the tires that come on most new cars are not noted for very good tread wear. Good quality replacement tires that are selected for long tread wear may last 3 times as long as the ones that new cars come equipped with.

    The sidewall of all tires sold in the US will have "scores" for tread wear molded into the rubber. A "new car" tire may have a tread wear rating as low as 150, and good quality replacement tires may have a tread wear rating of 600 in some cases. You get what you pay for, generally speaking.

    However, these tread wear numbers can only be accurately compared within one manufacturer's model line. In other words, a Goodyear tire with a tread wear rating of...let's say...300 will not necessarily have the same tread life as a Michelin tire with a 300 tread wear rating. The tread wear ratings are accurate only when comparing the same manufacturer's tires of different models.
  • edited June 2009
    I suspect when he said "they're like new" he meant that they were only partially worn and functionally there was no significant deterioration.

    Tires have "wear bars" molded in. When the spaces between the treads get close to the wear bars it's time to replace them. When you think about it, tires are one of the car's most critical safety items and as such are really, really cheap when you consider they can mean the difference between life and death. When in doubt, change them out.

    For a good primer visit www.carbibles.com.
  • edited June 2009
    "When a tire is brand new..." , too generic.
    A tire, which tire ? precisely , brand and tire name.

    I have a warehouse with 300 tires in inventory. NEW they vary from tire to tire. The samples I took just now, 9/32" all the way to 1/2".

    Tell us exactly your tire type, size, brand name, tire name. Or, knowing that, visit the website for that brand to view their specs.

    ------------------

    Miles driven on a set of tires is , again, entirely variable from tire to tire.
    The rubber composition ( the recipe they use when they mix up the batch of rubber ) is different for each brand AND each tire line within a brand.

    There is no simple, single answer.

    ---------------------

    Customers come to my parts desk and say they want some tires for their truck.
    "What size?"
    "uh, 17s"
    "what size 17s ?"
    ( deer in headlights look )
    After researching the size I show them a list with 40 different tires on it and get these huge eyeballs looking back . And that's just the list of tires in the Ford dealer program, not including all that are out there somewhere else.
    ( I've stopped showing the entire list now, and just discuss the ones in stock vs the type they want. Much easier. )
  • edited June 2009
    10/32 to 11/32 is brand new.

    7/32 is partially worn.

    below 5/32 is seriously compromised for winter driving.
    below 4/32 is compromised for wet driving
    2/32 or less is worn out usually legal limit.

    See how your tires wear and are working for you.

    For me my tires are at 5/32 and are ice skates and scary winter driving but still incredible in wet and dry conditions.
  • edited June 2009
    Thanks, all, for your answers and for the links. I learned a lot from them - mostly that there was a lot more to know than I realized!

    I assumed all tires started out the same. Now I see that's not the case, and why, and it makes sense.

    It's too dark out now to go see which kind of tires I have, and it's not on the receipt I have for today's work (patching a puncture from a screw and checking the tread wear). This was covered under my service agreement, so it was free and maybe they didn't feel the need to put in details? (Why they have every detail in there about the car and nothing about the tires, when it's the tires that the agreement covers I don't know.)

    Anyway, I believe they're Michelin tires. I know they're directional and top of their line, because I bought the best in order to have stability in rain and snow (but more in rain). I totally agree with you, the_same_mountainbike, about it being worth investing in them for safety.

    What I really was looking for was how much longer my tires have? Andrew J, your answer really helped with this. I gather I need to replace them before 2/32. It's not just about avoiding a blowout, it's that I wouldn't want to drive with them once they can't hold steady in rain and snow.

    Oh well, here's hoping I get a job well before the tires go and the car dies. It's 10 years old, has already had $1500 in engine and other repairs this year, has another $1000+ of repairs needed (engine mount, rear trailing arm brushes and then the brakes will be due for replacing soon and the transmission fluid, and the compressor needs replacing, too) and all this is even before the routine maintenance check, which I can't really afford...
  • edited June 2009
    Seven thirty seconds tread depth is good and nothing to worry about.
    Something you may consider is whether the tires are starting to suffer from dry rot.

    This can be caused by mileage, type of driving, environmental conditions, locale, etc. and is noticeable by tiny hairline cracking down in the tread depth or on the sidewalls.
    If dry rot exists, then the tires should be replaced no matter the tread depth. Hope that helps.
  • edited June 2009
    Thanks, ok4450, the dry rot factor is something worth knowing. I've heard about it before but I don't think anyone has mentioned it about these tires. I'll ask them to check tomorrow, when the car goes in for other maintenance.

    I know 7/32 is still good. I wanted to figure out how much longer they tires would be okay. I know it depends on all kinds of things, but is there come average for how long it takes to go from 7/32 to, say, 4/32?
  • edited June 2009
    Without the exact Michelin model name, this is a little speculation. If you have 60K on them, then you can expect between 10-12K more and possibly 20K more. Many top of the line Michelins are "warranted" for 80K miles. That is how I can up with this math.

    My own experience is that I have never gotten even 70K miles out of an 80K tire, particularly in the recent past. I tend to stick with 50-60K tires simply because I have had better "luck" with them, and tend to get the full warranted miles out of them.

    If I get down to about 4/32d and winter weather is coming on, then I would consider changing them early. 2/32ds is not a good tread depth for winter in the midwest.
  • edited June 2009
    When a tire is brand new, is it 7/32? Or 32/32?
    32/32...that's a new one.

    Those are inches....32/32 = 1"

    Truck tires don't have 1" tread.
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