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Old 12-20-2008, 12:13 AM   #1 (permalink)
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Will mis-match tire sizes burn up 4x4??


I had someone recently tell me that running mis-match tire sizes will ruin the 4x4 system in hurry. I do not have mis-match sizes but I do have different brand tires front to back. When I bought the truck the front tires were toast but the back were fine. One of the back tires has slightly more tread than the other but are otherwise identical. The front tires are of a different brand but the same size as the back. Shoud I be worried about running the truck in 4x4, considering the front tires are new and may be slightly "bigger" than the back?
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Old 12-20-2008, 12:26 AM   #2 (permalink)
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Slight differences shouldn't matter. When you have mis-matched tire sizes is when I would worry.
Old 12-20-2008, 12:28 AM   #3 (permalink)
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rear tires must be the same with the same amount of tread on them, because if one is smaller then your gears in the rear end are turning way to much then they need and you will burn up the rear.

Running same size tires are important when you have 4x4 engaged and have traction, it "could" bind up some stuff in the T-case. I'm no expert though :/ just what makes sense to me
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Old 12-20-2008, 12:30 AM   #4 (permalink)
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i don't think mis matched tires will mess 4x4 however, it is more about the tires circumference and or diameter if you know what i mean. Ed
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Old 12-20-2008, 09:23 AM   #5 (permalink)
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As long as you're using your 4x4 in slippery conditions only (rainy asphalt is NOT slippery enough), then it shouldn't matter. The slippery surface will allow the tires to slip. It's really no different from making turns with the center diff locked. If you're using your 4x4 on pavement, you're causing great stress to the components. Period.

This applies to part-time 4x4 only. If you have a viscous center coupling, then be very careful with your tire sizes. ...though even that isn't terrible if one's a little out.

As mentioned, I'd be more concerned with running mis-matched tires on the same axle than front to back. ...assuming you're not driving around on pavement with your 4x4 engaged.
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Old 12-20-2008, 10:33 AM   #6 (permalink)
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I have been told that different size tires will mess up the gears in the differential because the smaller wheel is spinning faster than the bigger one. never tested it but it makes sense. i would say that as long as the tires have the same size stamped on them but wear is different then it should be no problem. I have ran mismatched tires but the same size and had no problems
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Old 12-20-2008, 10:56 AM   #7 (permalink)
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Originally Posted by fifthand View Post

I had someone recently tell me that running mis-match tire sizes will ruin the 4x4 system in hurry. I do not have mis-match sizes but I do have different brand tires front to back. When I bought the truck the front tires were toast but the back were fine. One of the back tires has slightly more tread than the other but are otherwise identical. The front tires are of a different brand but the same size as the back. Shoud I be worried about running the truck in 4x4, considering the front tires are new and may be slightly "bigger" than the back?
Without knowing what exactly your drive train set up as long as the sizes are within .5-1 inch of each other you should be alright the slack in your drivetrain will allow for a variation of this much. Running different gear ratio's or substantially different size tires can cause your chain driven transfer case to go boom. as it is usually the weakest link. That being said I have a buddy that races in the mud bogs and he has 5.13's in the front axle and 4.10's in the rear, But the only time it is in 4 wheel drive is in the bog, and he still finds away for finding the weak link in his drivetrain usually with a big boom and grinding.
Old 12-20-2008, 11:12 AM   #8 (permalink)
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As said, drive on slippery roads and your tires will slip as needed.
If you were really concerned, even if all tires were the exact diameter, improper air inflation will offset tire diameter from front to back.
To match tire diameters as close as possible to minimize drive train binding, measure the rolling radius or each tire installed on truck, (center of axle to ground), and inflate tires as needed to match them. First inflate front tires to the required 55ish PSI, and then inflate rears to match.
If altering weight in rear of truck, to rolling radius will change accordingly.

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Old 12-20-2008, 03:29 PM   #9 (permalink)
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running diffrent size tires on the same axle will mess with more than your 4x4 system. over the summer I had a set of 265/75/16's on my truck and ended up with a flat. my spare was a 245/75/16. it messed with the brakes, making the brake with the shortest tire work the hardest. also I had to use the 4x4 on some wet grass and even with the slippage of the grass you could still feel a skip every so often. that being said if you have the same size tires and one is more worn than the other i would say no to worry about it to much, but to be on the safe side dont run around with the 4x4 on on dry pavement as stated above, expecially if you have a posi or even worse with a locker.
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Old 12-20-2008, 04:23 PM   #10 (permalink)
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Alright, to expound on what modified posted. Running mismatched tires (regarding their rolling diameter) will cause excessive binding in the 4wd components, namely the transfer case.
To check rolling diameter, with the truck on level lot, mark a line at the bottom of each tire (on the sidewall) (tape or wax pencil), and roll (drive) the truck forward for 10 tire revolutions as seen at one left side tire 'til the mark is at the bottom again. Any mark on the other 3, that is off by more than an inch, indicates a rolling diameter variation beyond acceptable, and it must be corrected to ensure the continued reliability of the 4wd components.
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