Replacing 1 tire?
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Thread: Replacing 1 tire?

  1. #1
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    Replacing 1 tire?

    My wife's 2007 AWD Sienna has one front tire in pretty good condition and one that is nearly bald. The rear tires are maybe 75% gone.
    I took it into a tire store to replace the nearly bald tire and they refused to do it. They say Toyota says that you have to replace all 4 tires at the same time or it will damage the transmission on AWD cars.
    I pointed out that his store has replaced one tire on three occasions on this very Sienna, and the dealer has replaced one tire twice. (The tires seem to attract nails like they have magnets in them...) All without damaging the transmission. Additionally, I have had two AWD cars for the past 15 years, have never replaced all 4 tires, without damaging the transmission. He still refused.
    I pointed out that the pretty good front tire will be closer in diameter to the new tire than it was to the nearly bald tire; yet the nearly bald tire didn't damage the transmission. That made sense to him and he agreed to put a new tire on.

    Now for the question...
    Is there any truth to this? Does Toyota really require replacing all 4 tires when one needs to be replaced, or is he just making that up? If true, we would have had to replace 20 tires when picking up our 5 nails. It also implies that putting a spare on will damage your transmission, as it certainly won't be the same as the other three tires.

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  3. #2
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    Re: Replacing 1 tire?

    The spare is not far off of the diameter of the original-equipment full-sized tires. It is a skinny spare, not a small spare.


    The logic of matching sizes is that different front and rear tire diameters mean that the outputs from the centre differential to the front and to the rear will run at different speeds, causing the centre differential to turn internally, just like an axle differential does while going around a curve... but a really gentle curve given the small difference in tire sizes being discussed here. The centre differential gears normally turn only due to the front/rear speed difference of going around a turn, so spinning continuously is not in their design conditions; I don't know if this is seriously an issue.

    The TRAC system will attempt to apply brakes to individual wheels which are deemed to be spinning (running too fast compared to the others). As long as TRAC is not triggered, I suspect that small tire diameter differences are not a big deal, but it would be nice to know just how much speed difference (and thus how much centre differential speed) is acceptable.

    The big concern with mismatched tires is for AWD vehicles with clutch-type devices (such as viscous couplings) between front and rear. The second-generation Sienna (such as Puffin's 2007) does not have a centre coupling of this type (it has an open differential), but the third-generation (2011) Sienna does. Those couplings can potentially overheat due to continuously engagement caused by a sufficiently large tire size difference, and it may be a reliability concern for the axle which is not normally driven (rear, in the 2011 Sienna) and may not be as capable as the normally driven axle (front, in the 2011 Sienna).

    Finally, it is not the "transmission" which can potentially be affected, but rather the differential used in the transfer drive (called a transfer "case", although we're really talking about the gears, not the housing).



    Ironically, going from a front combination of big ("pretty good") and small ("nearly bald") front tires to two big front tires ("pretty good" and new) will likely make the difference from front to rear worse, not better, even though it seems like a more even match. On the other hand, it will make life easier for the front differential, which has been tolerating a diameter difference which will have been causing a speed difference just as if the Sienna were continually turning toward the smaller tire.



    One method sometimes used to address the mismatch caused by a single tire replacement is to turn the new tire on a lathe to bring it down to match the others. This means throwing away good tire life on that one tire, but may be worthwhile to get the remainder of the life out of the other tires. With one "pretty good" and two more with only 25% left, I'm not sure that it makes sense to try to salvage the old tires... it's not like they're nearly new.

  4. #3
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    Re: Replacing 1 tire?

    I would look at the reason your tire is bald to start with get 2 new keep the good one for a spare the next time you lose a tire you will have a worn tire to use!
    2006 XLE Limited AFP

  5. #4
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    Re: Replacing 1 tire?

    Quote Originally Posted by brian_bp
    The spare is not far off of the diameter of the original-equipment full-sized tires. It is a skinny spare, not a small spare.


    The logic of matching sizes is that different front and rear tire diameters mean that the outputs from the centre differential to the front and to the rear will run at different speeds, causing the centre differential to turn internally, just like an axle differential does while going around a curve... but a really gentle curve given the small difference in tire sizes being discussed here. The centre differential gears normally turn only due to the front/rear speed difference of going around a turn, so spinning continuously is not in their design conditions; I don't know if this is seriously an issue.

    The TRAC system will attempt to apply brakes to individual wheels which are deemed to be spinning (running too fast compared to the others). As long as TRAC is not triggered, I suspect that small tire diameter differences are not a big deal, but it would be nice to know just how much speed difference (and thus how much centre differential speed) is acceptable.

    The big concern with mismatched tires is for AWD vehicles with clutch-type devices (such as viscous couplings) between front and rear. The second-generation Sienna (such as Puffin's 2007) does not have a centre coupling of this type (it has an open differential), but the third-generation (2011) Sienna does. Those couplings can potentially overheat due to continuously engagement caused by a sufficiently large tire size difference, and it may be a reliability concern for the axle which is not normally driven (rear, in the 2011 Sienna) and may not be as capable as the normally driven axle (front, in the 2011 Sienna).
    As I understand it:
    1) There is no difference between AWD and FWD regarding differences in size between the front two tires. Since tire size is not a big deal for FWD cars, it shouldn't be a big deal for mine either. The TRAC has not engaged.
    2) The big problem with mismatched tires is only on the 2011 Sienna; not on the earlier ones. That might explain why both the dealer and the tire store were willing to install single tires with previous tires; the tire store heard something about mismatched tires and thought it applied to all Sienna, not just the 2011.

    Obviously there are no guarantees; but is that about it?

    Why would Toyota change AWD systems? Having to replace all your tires everytime seems like a killer to me.

  6. #5
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    Re: Replacing 1 tire?

    Quote Originally Posted by komondor
    I would look at the reason your tire is bald to start with get 2 new keep the good one for a spare the next time you lose a tire you will have a worn tire to use!
    The tires have picked up 5 nails that have required new tires in 70,000 miles. (previous to that I have probably gotten 5 nails in 500,000 miles; but that is a completely different question). My guess is that somehow the bald tire is simply a survivor.

    Of course that raises the question of why the dealer didn't notice the problem at the last oil change 5,000 miles ago; it should have been pretty darn close to needing replacement then.

  7. #6
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    Re: Replacing 1 tire?

    Toyota got back to me.
    They recommend having all the tires similar in size to reduce wear on the differentials.
    So, replace both if the other one isn't in good shape, or all 4 if the other 3 aren't in good shape.

    I probably should replace the rear tires...

  8. #7
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    Re: Replacing 1 tire?

    Quote Originally Posted by Puffin
    Why would Toyota change AWD systems? Having to replace all your tires everytime seems like a killer to me.
    Cost.

    One challenge with a transverse engine and transaxle - and a reason that Subaru stays with their strange longitudinal drivetrain configuration - is that it takes a lot of moving parts to fit in a centre differential in the power flow between transmission and all wheels, and get a shaft headed to the rear. The clutch-type systems can leave the drive path to the front quite direct, and just tap off the drive to the rear. There are all sorts of implications to handling, tire wear, drive transmission efficiency, and reliability, but clever control of that clutch can make the system work well.

    It seems that all transverse-engine Toyotas are going this path; the RAV4 and Highlander have also made the change from the centre-differential design to the rear-drive-by-clutch scheme, in earlier model years.


    I don't know that replacing all tires together is a big deal to most owners, since regular rotation evens out wear and I think most people rarely lose a tire to a road hazard.

  9. #8
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    Re: Replacing 1 tire?

    You have AWD which suggests that it's winter where you are and you expect snow. In that case, I think you made an error in not replacing at least 3 tires, and probably the 4th as well, though I don't know what you think of as "pretty good."

    I imagine that you compounded your error by buying cheap tires.

    If there's one place on a vehicle NOT to try to save a few bucks, it's the tires. They're too important.

    I think you're right to question your dealer service department. If they were properly thorough, they'd have caught it.
    2011 Toyota Sienna Limited AWD with Premium and Convenience packages in South Pacific Pearl over Light Gray purchased 03/31/2010
    • (CF) Carpeted Floor Mats with Door Sill Protectors
    • (GN) Cargo Net

  10. #9
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    Re: Replacing 1 tire?

    Quote Originally Posted by Qest T. Silverclaw


    I imagine that you compounded your error by buying cheap tires.
    Tires are $220 at the tire store and $320 at the Toyota dealer.
    If they are cheap, I hate to think what expensive tires cost.

  11. #10
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    Re: Replacing 1 tire?

    That definitely sounds like Canadian pricing. What model tires did you end up running?
    2011 Toyota Sienna Limited AWD with Premium and Convenience packages in South Pacific Pearl over Light Gray purchased 03/31/2010
    • (CF) Carpeted Floor Mats with Door Sill Protectors
    • (GN) Cargo Net

  12. #11
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    Re: Replacing 1 tire?

    Quote Originally Posted by Qest T. Silverclaw
    That definitely sounds like Canadian pricing. What model tires did you end up running?
    Nope US. Bridgestone B380. That is installed and after all tax and charges. Tirerack is $145 for just the tire, so $220 isn't so bad.
    The dealers price is absurd, but I guess they have to make up for selling the cars at a loss.

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