# Tire question



## Bigplanz (Apr 10, 2009)

2000 Lincoln Navigator, AWD. The rear two tires are worn out, the passenger side rear the worst. The two on the front were replaced last year, and have less than 10K miles on them. P-255-75-17, Goodyear Wranglers on the front, which is what I am going to put on the back.

The tire guy at Goodyear said that AWD cars have to have tires that are within a certain tolerance of equal tread depth or the transmission can be damaged.

Is this true? I certainly need 2 new tires in the rear, but at $200 a pop, i would rather do one first and the other maybe next month. As I understand the transmission in this SUV, the base driving condition is rear wheel drive, and AWD only begins to engage "on-demand" if the computer senses a wheel is slipping. In a slipping condition, power is transferred incrementally to the front wheels to correct the slip. I don't think two tires are necessary (though desirable), but would like some informed opinions. Oh, don't know why it would matter, but the two tires on the back are Perilli's. Thanks.


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## stick\shift (Mar 23, 2015)

It's at least generally true. Old man used to work for Subaru and their tolerance at the time was all four tires had to be within 1/8" of each other in height.


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## Bigplanz (Apr 10, 2009)

stick\shift said:


> It's at least generally true. Old man used to work for Subaru and their tolerance at the time was all four tires had to be within 1/8" of each other in height.


That was pretty much what the tire guy said. I am sure it is true in a general sense, but my AWD isn't full-time, it's on-demand. 99% of the time, the Navigator is in RWD. I don't think it has ever been in 4WD. I know for sure it hasn't since I have owned it.


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## Oso954 (Jun 23, 2012)

I think you need to check the rear differential
If it is limited slip, the size difference could cause excessive wear on the diff.

LS is functional regardless of the awd selector position.


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## Nealtw (Jun 22, 2017)

Put the matching tires on the back and odd ones on the front. Buy the last tire ASAP.


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## Bigplanz (Apr 10, 2009)

FWIW, I read the owner's manual and it didn't say anything at all about this subject. It just said that all the tires should be the same size and tread pattern. The two perelli's have been on the back of the car since I bought it, and the other two i bought one at a time last year. This is the first time anyone has said anything about the size concern. 

I assume that since the owner's manual doesn't say anything about this issue that it isn't one.


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## Bigplanz (Apr 10, 2009)

Found a Ford manual for a front wheel drive/AWD car. At least in that particular vehicle, Ford indicates worn and new tires can be used without damaging the AWD system. Can't find anything specific to the Navigator, Expedition or F-150

"Major dissimilar tire sizes between the front and rear axles (for example, 17 inch low profile tires on the front axle and 22 inch high profile tires on the rear axle) could cause the AWD system to stop functioning and default to front-wheel drive or damage the AWD system. However, the AWD system is capable of tolerating any combination of new and worn tires of the same original tire size. For example, using 3 worn tread tires and 1 new tread tire all of the same original tire size, can be tolerated by the AWD system."


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## Oso954 (Jun 23, 2012)

> I assume that since the owner's manual doesn't say anything about this issue that it isn't one.


Bad assumption. There are a lot of things that Ford doesn't put in the owner's manual.

Even some of the stuff they do put in the manual or on the door sticker isn't always the best info. Remember the Explorer tire pressure/roll over problem. I think everybody in the automotive/tire business knew 26psi wasn't right for that vehicle. Explorers of that vintage were nicknamed Ford Exploders.


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## ZZZZZ (Oct 1, 2014)

Bigplanz said:


> I assume that since the owner's manual doesn't say anything about this issue that it isn't one.


I wouldn't assume that. I used to write user guides and instruction manuals for a living. Lots of info doesn't get put in there: to keep things simple, to keep it brief, or management just doesn't want to "go there" at the consumer level.

I would check the Ford/Lincoln website and see if there is any relevant info there. If not, there should be an email address or phone number to call for technical questions like yours. Surely this issue has been raised many times over 17 years..
.
.


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## Nealtw (Jun 22, 2017)

Bigplanz said:


> Found a Ford manual for a front wheel drive/AWD car. At least in that particular vehicle, Ford indicates worn and new tires can be used without damaging the AWD system. Can't find anything specific to the Navigator, Expedition or F-150
> 
> "Major dissimilar tire sizes between the front and rear axles (for example, 17 inch low profile tires on the front axle and 22 inch high profile tires on the rear axle) could cause the AWD system to stop functioning and default to front-wheel drive or damage the AWD system. However, the AWD system is capable of tolerating any combination of new and worn tires of the same original tire size. For example, using 3 worn tread tires and 1 new tread tire all of the same original tire size, can be tolerated by the AWD system."


They just put this in there in case they have to supply a new tire under warrentee :devil3:


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## de-nagorg (Feb 23, 2014)

I'm with nealtw on this.

Put your two front tires on the back, then buy a new one for the worst wore one and put it on the front along with the better of the two Pirellis, Then in a month when the budget can handle it get a new one to replace the last old one.

But in good practice buy all four at the same time if at all possible.

I realize that not everyone has a spare Grand lying around to buy new tires.

So just be careful while driving the one old tire, no mud bogging, or excess running in slick conditions, and the wear will be kept to a minimum.

ED


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## Brainbucket (Mar 30, 2015)

I found this;
From a Ford Special Service Message (SSM): 
19235 1996-2007 Multiple vehicles - check tire circumference and tire inflation. 
Some 4WD vehicles equipped with control trac/intelligent 4WD/all wheel drive may exhibit a shudder on acceleration, noise from the front driveline and/or transfer case, axle windup and/or binding while driving and being operated in the 4x4/auto 4x4 mode. Other 4x4 vehicles equipped with (manual or electronic shift) and a 4x2 mode may also not shift on the fly to 4x4 auto or 4x4 high at highway speeds. This may be due to incorrect tire circumference or improper tire inflation pressures. Four wheel drive and all wheel drive vehicles require that all four tires have the same circumference. Verify that all four tires have no more than 1/4 inch variation in circumference and that they are inflated to the proper tire pressures.:vs_cool:


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## Nealtw (Jun 22, 2017)

So the tire guy could match the tire size with air pressure 1/4" circumference is nothing on the diameter.


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## Brainbucket (Mar 30, 2015)

Nealtw said:


> So the tire guy could match the tire size with air pressure 1/4" circumference is nothing on the diameter.


No. The air pressure should be at manufactures specs. The circumference of the tire should be not over 1/4 in difference. Also just a note. Different air pressure from side to side will cause a pull.:vs_cool:
*Verify that all four tires have no more than 1/4 inch variation in circumference and that they are inflated to the proper tire pressures.*


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## Bigplanz (Apr 10, 2009)

A couple of pictures of the bad tire. It's really about a year overdue for replacement. Tread separation and dry rot in the sidewall. Examples of both are circled in blue. Separation appears to be the result of age and a design flaw. Perelli put an angled groove on the side of the tread, and this groove became the location of weakness that promoted separation. This is one is gone tomorrow, the other one (not so bad, but is bad) gets replaced two weeks from now. 

Check those tires guys! I didn't realize how bad they were until I took pictures and enlarged them on my computer.


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## Nealtw (Jun 22, 2017)

Brainbucket said:


> No. The air pressure should be at manufactures specs. The circumference of the tire should be not over 1/4 in difference. Also just a note. Different air pressure from side to side will cause a pull.:vs_cool:
> *Verify that all four tires have no more than 1/4 inch variation in circumference and that they are inflated to the proper tire pressures.*


One new one can't be much worse than one bald one.:vs_coffee:


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## de-nagorg (Feb 23, 2014)

Bigplanz said:


> A couple of pictures of the bad tire. It's really about a year overdue for replacement. Tread separation and dry rot in the sidewall. Examples of both are circled in blue. Separation appears to be the result of age and a design flaw. Perelli put an angled groove on the side of the tread, and this groove became the location of weakness that promoted separation. This is one is gone tomorrow, the other one (not so bad, but is bad) gets replaced two weeks from now.
> 
> Check those tires guys! I didn't realize how bad they were until I took pictures and enlarged them on my computer.


See red: Sounds like a great plan.

Yes those tires are ready for the recycler.

ED


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## Oso954 (Jun 23, 2012)

Buy replacements for both tires, today.

I wouldn't be comfortable driving on those at city speeds, much less hiway speeds.


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## ZTMAN (Feb 19, 2015)

My guess is you have already been doing what the GY man told you could harm your AWD system. I would assume those Perellis are a different diameter than the GY. Put a tape to them

I would go with four tires myself. I just got a set of 20" GY Wrangler Silent Armors for my Suburban for around $650. Included tax, mounting etc. That is with using the GY credit card since they give you a $160 rebate.

They are great tires.

As a side note, if you are looking at the Wrangler SRA's, your size is the same size as a Jeep Wrangler Tire. Tons of brand new takeoffs around on craigslist. IE here is an ad for new tires and wheels for $475. Use the tires, scrap the wheels.

https://harrisburg.craigslist.org/wto/d/2017-jeep-brand-new-tires/6332197720.html


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## mark sr (Jun 13, 2017)

I would prefer to not even have that tire as a spare!


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## Bigplanz (Apr 10, 2009)

Well the tire's replaced, but the lug studs are damaged. Replacing them requires opening the differential, separating the axle, them pulling it out a couple of inches to have enough room to get the old ones out and the new ones in. Then, reattach the axle, close up the differential and replace the gear oil.

Right.

Video at pull a part. (I was cussing the camera at the beginning. Oh, the correct oil is 75X140, synthetic.))


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## Bigplanz (Apr 10, 2009)

What the axle looks like if you pull it out. You don't have to pull it competely out, just enough to get the old lug studs out and the new ones in.


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