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41" on the ground 40"spare?

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  • 41" on the ground 40"spare?

    I'm getting ready to replace my tires on the PXL and I intend to go with 41" IRoks. My spare is a 40" Toyo. Obviously, there's a small decrease in diameter but will this affect any thing of I only use it for a spare? The front is an open diff so if I must I could always install the spare on the front.

    Thoughts? Cautions!

  • #2
    It's possible to limp home on a mismatched tire, but it's really the wrong thing to do. Your spare should match the 4 on the ground. Really, the correct way to do it is with a 5-Tire rotation, so they wear the same (and last 20% longer), but this is a hassle with directional tires like the IROK since you have to dismount and flip the spare periodically.


    • #3
      On a tire that size, the difference in overall height and rolling circumference is roughly 2.5% which isn't huge but some AWD cars can have problems with less than a 1% (approx. 1/4") difference. Even though the front might be an open diff, unless you have free spinning hubs then the front axles are always engaged and get disengaged at the transfer case, so there could still be some wear. I double-checked the owner's manual about this. There isn't a lot about it. The closest thing I found was this:

      It is recommended to replace the two front or two rear tires as a pair.
      Other than that, the next best I could find was related to using a temporary-use spare vs a full-size spare. It did not specifically call these out as being undersize but that seemed to be the implication. In general, my takeaway is that if you are using it for "emergency use only", keeping the distance as short as possible, and not engaging your 4x4 unless critical, then you'll probably be fine. Most of the issues with mis-matched tires come from driving them on the road as your normal configuration for many thousands of miles. For a few miles (maybe up to 100 miles) I don't think you have much to worry about.

      My other recommendation would be to plan your tire rotations to include your spare tire. That way you extend the overall life of your set of tires, but also you avoid the problem of having an unused spare tire in a different size in the future. Of course, you're also buying 5 tires when you need a new set, but that's what I do on my truck in order to keep everything in balance, to ensure that the tire does not become a liability through lack of use. A sitting tire isn't a good thing, they should be exercised regularly along with the rest of your tires. Here's how you would rotate that spare in:

      Use our Tire Service/Maintenance Record (PDF) to log tire rotations, seasonal tire changeovers and tire-related vehicle services. This type of record is often helpful if warranty consideration is ever necessary. Download Now! Tire Service/Maintenance Record (PDF) We all hear that tire...
      Attached Files


      • #4
        Thank you for your replies. I have decided to just order 5 tires to remove any doubt. Now, I just hope they fit well. I expect a little rub.


        • #5
          41" IRoks have been installed. They are all around less compliant than the Toyos but not bad by any stretch. I may start a separate thread for those who're interested.


          • #6
            I'd be interested to hear how you like them (and of course pics!).


            • #7
              Originally posted by Thrust View Post
              41" IRoks have been installed. They are all around less compliant than the Toyos but not bad by any stretch. I may start a separate thread for those who're interested.
              Definitely interested in hearing more feedback, whether on this thread or a new one. I'm curious to know what you mean by "all around less compliant".