AWD Tire Replacement

[Bdt1967]

Hi all, new to the forum! I purchased an AWD Mountaineer last weekend, on the drive home the car got a flat. I put the spare tire on, and drove it home. Since the tire is on a factory wheel, and has new tread on it, I assumed I would just drive it for a while. However, I began to worry that the difference in tread would cause problems with the AWD. Since the original tire is destroyed I am going to have to replace it, but I have been told since its an AWD I need to replace all the tires, thats going to hurt the pocket book quite a bit. I would think I should be able to put new tires on the back and run the fronts for a while, would this be correct? There are a variety of opinions when I searched the forums, but I need to know whats correct. I hate to throw away 3 good tires because I have one bad one.

Thanks
Andy

 

[waskly]

awd needs 4 matching tires, on 4x4 manual you can probably get away with bad tires on front or rear and new on the ohter. on awd you need 5 matching tires, (spare too)

so if you buy 4 tires, match it to the spare.

awd always works, 4x4 also semi always works, hence why i said 4x4 manual you can get away with it.

you are correct in that you need 4 new tires, also, you need a matching spare, its cheaper to match to the spare then buying 5 tires.

 

[my pos mounty]

awd needs 4 matching tires, on 4x4 manual you can probably get away with bad tires on front or rear and new on the ohter. on awd you need 5 matching tires, (spare too)

so if you buy 4 tires, match it to the spare.

awd always works, 4x4 also semi always works, hence why i said 4x4 manual you can get away with it.

you are correct in that you need 4 new tires, also, you need a matching spare, its cheaper to match to the spare then buying 5 tires.

Not to mention the fact that buying the 5 tires will be cheaper in the long run than not buying a matched set.

You could measure the outer circumference of the tires you do not want to replace and the one (or two) new ones. If you find more than a 1/4th inch difference between them, bite the bullet and do all 5.
That 1/4th of an inch rotational difference will have to be absorbed by the viscous coupling (VC) in your transfercase. Too much of a difference in rotational speed and the VC will overheat resulting in its failure. The failure of the VC will cause the vehicle to literally drag the tires that are of the smaller circumference. That can cause a severe amount of excess heat in the differentials, which in turn will slowly cook them and your transfercase.
The differentials in the third gen are notoriously weak already, and with just rear differential alone costing around $1100, 5 tires (mounted, balanced, filled with nitrogen with new valve stems and roadside assistance plan) is cheap in comparison.

 

[Joe Dirt]

Not to mention the fact that buying the 5 tires will be cheaper in the long run than not buying a matched set.

(dead link)

Ah, you are wise...

Yes- both above posts are correct!

 

[Bdt1967]

Thats what I was afraid of. Oh well, it will be nice to have new tires. Thanks for the advice!

Andy

 

[jrford]

i didn't have a blowout, just 4 very worn tires. Also having read a lot on AWD (Viscous, no switches) tire size if very important for the longevity the xfr case, like other stated above.
With our '04 the spare was only a black steel rim so i had to buy a stock rim from a JY for about $100, and TPS. Mounted 5 new tires (sig below) and i'm working on a 5 tire rotation, very 4k miles, I do it with my oil change. Hopefully the whole set will last longer, i got about 70-80k on a similar set so maybe, cross my fingers i'm hoping for over 100k.

Another idea is if i have a blow out like you with say 50k on them, i don't have to buy 4 new ones but instead switch to a 4 tire rotation for the rest of life, and never use the spare again.
BUT knowing that sometimes money is tight there is another option for you, i haven't done it myself but heard you could 'shave' a new tire down (use the same size and brand of course), more or less accelerate the wear to where they match the other 3. Might have to call around and see if anyone can do it.

 

[Bdt1967]

Yeah talked to the wife last night, we just decided to get a full set, kinda sucks but whatever. The worst part is I ordered the tires and its going to take 5 business days to get them. Since we need to have 2 vehicles, I am going to have to patch the old tire, or drive on the spare. I talked to they guy at Ford, and he assured me it would be fine for a couple days till the tires come in, but I am not sure I believe him.

 

[my pos mounty]

Keep the rides short and don't hammer the accelerator much. Your enemy is the heat the VC will create. The longer/harder you drive the more heat will be generated.
Replace the tires as soon as you can, a few days of necessary running around shouldn't be the death of it unless it was well on its way anyway.

Good luck

 

[Bdt1967]

My wife only drives it about 4 miles to work, and 4 miles home in town, so its low speed 30-40 mph driving. Should be good?

 

[my pos mounty]

It should be fine

 

[Bdt1967]

Cool, thanks!

 

[Robsbrd99]

Hey guys,
If someone could check my math here, I put the tape measure on the ground went up the tire, bisecting it in middle and got 28.25 inches. on my tires. I think im fine, but, when I bought mine, it had two pretty new looking tires and two sorry looking tires. I made them put two more on it. Now, Im sooo glad I did! Didnt know Awd's were like this.
Is there a way to disable the Awd if you have a flat and want to drive with the spare for a while? Like maybe pulling a fuse?

 

[jrford]

there is something called a 'chalk' method that measures the Circumference, i heard spec was less than 1/2" difference.

Only way to disable AWD is to remove the front drive shaft, thus no fuse to pull.

 

[Robsbrd99]

Gotcha, Thanks!
I forgot i had a tread depth gauge. Went out today and checked them and it looks like there all between 9 and 10/32 all around.
I had the transfer case drained about a year ago. Guess I now know why the fluid was kinda dark.