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Ryan_V

replacing one tire on an AWD

16 posts in this topic

will just replacing one tire on a newer AWD suv mess up the diff?? my dad had a nail in the tire of his Mariner. He was just going to replace it, but doesn't want to replace them all cuz there's only 25000 miles on them. He was told that if he only replaces one, that the diff will burn up because the AWD sensor will sense the difference in tread and the will throw things out of wack. He was told that he should replace all 4, that even replacing 2 might mess things up... any advice from you guys out there that know about such things....in exchange for good info, I'll provide info about what I know about...drinking beer and sitting on the couch grin.gif in all seriousness, thanks in advance!!!

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I wouldn't walk away from that tire dealer -- RUN! Someone is trying to rip you off! Changing several tire sizes might cause a differential problem, but normal wear of 25,000 miles is definitely not enough to cause problems.

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Not to mention the fact that even among like tires there are small inconsistencies.

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An All-Wheel drive vehicles tires should really be replaced in 4's could you get away with one at 25,000? it depends on the shape of the other 3 tires.....I suppose.....I wouldn't.

Todays differentials are quite spendy to say the least.

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I've rebuilt enough differentials in my life to know that simply turning a corner puts more wear and strain on it than driving down the road with tires that are a few 32nds difference in size ever will. Heck, not rotating them frequently will cause a difference in wear of several 32nds from front to back (or side to side). I guess I would decide whether or not to buy a full set more judged on how much wear the others have, not because someone told me a bogus story. If the other tires were rotated, kept inflated properly and driven on sensibly, they could very well have good tread life left. If the remaining tires have good life left in them, it would be foolish to buy a full set.

I would however add that if you are unable to get the EXACT same tire brand, in the exact same size, then all of the above goes out the window.

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If I was to offer my opinion, it would be totally based on the tread depth of the tires. I would say that you should replace 2 for sure if the difference is great enough. Definitely not 4.

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Although the tire saleman may have had an ajenda and your tires may be fine at 25,000 it is not totally bogus to suggest replacing all 4 tires on an ALL WHEEL DRIVE vehicle as a rule of thumb.

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I'm with you, I overhauled over a hundred before I left the industry. What people fail to understand/realize, is that the average all season truck tire is say, about 17/32nds new and last 45-60 thousand miles depending on the tire and driver. This would leave a difference of say,8/32nds difference between the new tire and the other 3. That equals a 1/4" of difference, so small of a difference that 5-8psi of inflation difference, an uneven load etc. would have a much greater effect. The marketing of the tire industry is incredibly successful if they have convinced people that a differential is so sensitive and complex that an air filled rubber tire that moves up, down, sideways and squats as little as a 1/4" will destroy it.

Maybe I should have been selling tires all those years...

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Recommending all four is not out of the question for an all wheel drive vehicle. I have seen some funky issues with jeeps and fords with worn out tires on one axle and new tires on the other. Without seeing or knowing the kind of tire you have, how much tread is left, and what kind of tire you where purchasing it is not possible to say yes you need all four or two will do. If you where purchasing a different model or brand than the original equipment than for sure all four whether or not the others are good or not. The difference in the handling of the elements between the mismatched tires should be a concern with AWD as well as all drivetrain setups.

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I agree, and know the issues you speak of with the Ford product, replacing 2 tires on one axle, ending up with a big difference in revolutions per mile between the front and rear axle. Wheel speed sensors (the ABS ones) can pick that up and in rare cases sense tire slip and engage all wheel drive. This will not, however, burn up a diff due to nonexistant AWD sensors as this salesperson implied in his effort to convince, scare, or whatever to try and sell this kids dad 4 new tires. The car is not that darn smart.

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I recently purchased a Subaru AWD Outback,,,,since then I have done a lot of reading at a subaru enthusiest (SP) web site ,,,they are just owners with no agenda and they are pretty adament about tire circumfrence,,,, stating that all 4 tires should be less then 1/4 inch circumfrence difference ,,,it has been mentioned that some tire dealers will shave down the thread to the same circumfrence as the other tires

Good Luck

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If it were mine I put a plug in the tire.

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 Originally Posted By: Surface Tension
If it were mine I put a plug in the tire.

Me too, unless it was in sidewall of course. I had bad expereince with a tire (same brand) of different circumference on a Ford Ranger, due to the same thing as the original poster says. Holy cow would that that front end jump when in 4wd at every 9/10 of a mile.

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 Originally Posted By: LoonASea
I recently purchased a Subaru AWD Outback,,,,since then I have done a lot of reading at a subaru enthusiest (SP) web site ,,,they are just owners with no agenda and they are pretty adament about tire circumfrence,,,, stating that all 4 tires should be less then 1/4 inch circumfrence difference ,,,it has been mentioned that some tire dealers will shave down the thread to the same circumfrence as the other tires

Good Luck

Wow! If thats the case, I hope when those guys air up their tires they measure them rather than use an air guage, otherwise they are gonna be unhappy! There are small inconsistencies in every brand tire that will cause each one to be slightly different, even at exact air pressures.

I found on the Mercury website that the standard tire size for the vehicle in question is P235/70R16. Different brands of that tire have anywhere from 11/32 to 14/32nds. If you wear off 1/4 inch of tread (8/32) even on the tire with the deepest tread 14/32nds (new).... close to 3/4 of the tire life is gone at that point. (Assuming 3/32nds as the absolute minimum before replacing) On the one with 11/32 (new) that tire is already shot and should be replaced anyway! What was said, is if the other tires were measured and in decent shape, there is no need to replace them all.

The closest I can calculate, on a tire that size, a tire with 8/32 less tread will turn only 4 to 5 more revolutions than a brand new one will in one mile.

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,,,they are just owners with no agenda and they are pretty adament about tire circumfrence,,,,

That is my point, "just owners" not the trained professionals/experts if you will, who have earned a living keeping these things working. The average owner does not have the experience or understanding of these systems let alone working on dozens or more of the same model to really gain good comparative knowledge.

I am in total agreement with the premise of replacing all four tires when it comes time for tire replacement due to wear, driveline symptoms can and will arise when one tries to cut corners in relation to tire size differences from front to rear axles. This was not the original question to which I responded, however, and I continue to stand with my original answer.

I will acknowledge that the best solution was from Surface Tension.

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 Originally Posted By: BoxMN
 Originally Posted By: Surface Tension
If it were mine I put a plug in the tire.

Me too, unless it was in sidewall of course. I had bad expereince with a tire (same brand) of different circumference on a Ford Ranger, due to the same thing as the original poster says. Holy cow would that that front end jump when in 4wd at every 9/10 of a mile.

\\

it is of course in the sidewall...thanks to whomever called me a "kid"!!!! I like that!!

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