4-wheel drive vehicle and inconsistent tire size

What is the acceptable tolerance on tire size differences for a 4-wheel drive vehicle? I recently had to put my spare tire on a severely punctured tire on my 94 Explorer. All five tires are from the smae manufacturer and purchased at the same time. Due to normal usage, the tread wear on the existing tires compared to the unsued spare measured about an inch larger in circumference for the spare. I was told that due to that one inch difference, while engaged in 4-wheel operation would cause damage to the tranfer case. While the existing tires are still in execellent condition, does that mean I have to replace all four tires as recommended?

Perhaps this is obvious in hindsight, but this is why you should do 5 wheel tire rotations.

I think you’re kind of in the gray area here. Firstly, four wheel drive vehicles are not as sensitive to this as all wheel drive ones where all four wheels are powered all the time. What wears out on AWD vehicles is the center differential, which is what allows the front and back axles to turn at different rates, allowing you to turn. Your 4wd vehicle doesn’t have one of these-- when you’re in 4wd the front and rear axles are locked together and turn at the same rate. So when you’re in 4wd, you have to be on a slippery surface so the wheels can slip a little to allow you to turn.

There is no chance of damage to the transfer case because the differential for the axle that the odd sized tire is installed on will just compensate and send more rotations to the bigger tire and fewer to the smaller one. This is a little hard on the differential, but if you install the tire on the front, the front differential is usually disengaged and it shouldn’t be a problem. However, it will cause a slight power bias to that direction when you’re in 4wd, although I don’t know how noticeable it will be. You might try to just go ahead and get the tire put on and then go try it out in some mud or snow and see how it does.

Different tire sizes on a 4WD vehicle isn’t going to effect the transfer case. You’re thinking of an AWD vehicle and the damage it can cause to the center differential.


I don’t think small differences in tire circumference are a big issue with 4WD vehicles, since you only engage 4WD off road or on slippery surfaces like snow.

Tire circumference matters very much on many ALL WHEEL DRIVE (AWD) vehicles, however, and damage can occur if the tires are not closely matched.

If, for some reason, you wanted to engage 4WD on dry roads (not recommended), then there might be a problem.

Do not install the older tire and newer tire on an axle with limited slip. It will damage that. It won’t damage the transfer case but will stress the other componets.

You will have to buy one new tire anyway. So, put your spare and the new tire on one axle and make one of the older tires be your new spare. This way you will have no tire size difference on either axle.

Is the Explorer actually 4WD, or is it AWD?

In case this vehicle’s drive system is, in fact, AWD, then different tire circumferences can lead to some expensive repairs to the center differential.

Veterans of this board can probably anticipate what I will now ask:

Has Byoung 09 read what the Owner’s Manual has to say on this topic?

As with virtually everything else regarding the safe and economical operation of a vehicle, the Owner’s Manual should have the authoritative answer.

Thank you all for take the time to provide your valuable knowledge. At least now I use those reliable resources to support my decision.