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different tire sizes on front and rear?

Hi guys,



This is Christy, aka weecamlass from the old forum (they said I couldn't use my old name because it contained "inappropriate words" - would that be the first part of the name or the last?)



Anyway, after teasing my boyfriend about his failure to buy new tires until it was (almost) too late, I decided I'd better take a good look at the ones on my own 2000 mazda protege LS (188,000 miles, driven about 15,000 a year). When I did, I discovered the tires on the front and back are different sizes!



I bought 2 new tires when I got the car 2 years ago (I know you're supposed to buy 4 at a time, but I'm on a budget here). The newer ones are on the front, and they're the correct size according to the owners manual: 185/65. The ones on the back are 175/65. No one, including the guys who installed the new tires, ever pointed this out to me.



Is this bad? I check tire pressure regularly and the car doesn't seem to have a problem, but I want to make sure I'm not hurting anything.



The other question is: I guess I've been lame about rotating tires. I was about to have that done, but now I'm guessing that's not a good idea given the different sizes. How important is it to rotate the tires?
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Comments

  • edited June 2007
    d'oh...I meant the car has 88,000 total miles, not 188,000
  • edited June 2007
    It should not be too much of a problem if you make sure to keep the like pairs on the same axle, that is both on the front matching and both on the back matching. You also want to keep the best tyres on the back.

    If you were to mix them so both of one size were on the left and a different size on the right then in an emergency stop you would not stop straight. The reason to keep the best tyres on the back is likewise safety in an emergency because if your back tyres are not as good or better than the front, you may end up looking where you have been and not where you are going.
  • edited June 2007
    In this case the tires are the same diameter, so it's not a real big deal. They are a different width, but the ones that are the wrong width are (presumably) the next ones you'll replace. If you don't drive like a maniac you should be fine until it's time to replace them.

    Russ
  • edited June 2007
    Actually, the 185 tires are about 2% larger diameter than the 175 tires, but it should be OK if they are are kept on the same axle. As others have said, put the new tires on the back and replace the front tires with the matching size when they wear out.

    When you have good tires on all four wheels, you can have them rotated every 5000 miles or so. Most tire shops will rotate them for free when you buy their tires.
  • edited June 2007
    The smaller tire is about 2.3% smaller in diameter so your speedo will have a 2.3% error; will read high as will your odo when you have the smaller tires on the drive wheels. Verify this by Googling Tire Size Calculator.

    I ran 155s and 165s on a car until the wrong size wore out; I couldn't notice the difference.

    As was said, rotate but make sure that you keep the same size on the front and the same size on the rear.
  • edited June 2007
    When you buy tires a store that advertises based on low prices, and you go in saying you want inexpensive tires, they sometimes will sell you a tire a size smaller to keep the price low. That happened to me, but I caught it the same day and returned them for the proper size tire- they didn't charge more, but you have to pay attenion these days..as the other posters have said, no real problem, just keep the same size tires on the same axle.
  • edited June 2007
    so it sounds like it wouldn't do any good to move the drivers side tires to passenger and vice versa?

    I wonder if the people who owned it before me got ripped off by the tire place, as you suggest. I honestly don't remember the size of the tires I replaced two years ago, but the old ones are cheapo tires, so I wouldn't be surprised if that's what happened to them.

    Another question: do front tires wear out faster on a front-wheel-drive car? The new tires are on the front wheels, but the (cheapo) back tires seem to have as much tread as the front ones.

    Thanks for your help!
  • edited June 2007
    Another question: do front tires wear out faster on a front-wheel-drive car? The new tires are on the front wheels, but the (cheapo) back tires seem to have as much tread as the front ones.
    Yes the front tires will wear faster, I would put the new tires on the back and replace the front tires with the proper size when they wear out.
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