Is smaller spare ok on AWD?

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Is using a smaller diameter tire ok or will it cause problems on my 2004 AWD Durango? I want to replace the stock 245/70/17's with 265/65/17's but would rather not have to buy another spare as well since the spare
has never been used and is only a year old.
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That was a problem with posi but I'd doubt that any harm would occur. Not to say that running a mismatched tire is great for handling or prolonged use.
Roy
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It won't hurt a thing as long as the spare is never used. If you have to put the spare on the ground however it can cause damage to the drivetrain.
Mike
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Ditto. Any odd sizing of tires on 4WD or AWD will cause additional drivetrain stress and must be avoided.

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RCSnyder wrote:

I was under the impression that stress would only occur if the differentials were locked. In the case of AWD they are not unless I switched it to 4WD locked mode.
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That would be my thought as well. If all wheel drive is not engaged, and even if it is, is it truly "all wheel drive"? I was under the impression (although perhaps wrongly) that all wheel drive used open differential's.
Roy
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It is not as simple as that. While the transfer case in a AWD has a diff of sorts inside of it, it is not an open diff, more like a limited slip with locking capability. If you put a smaller tire on either axle, it is going to cause that axle to turn at a different speed than the other one all of the time which will cause a continuous load and forced slippage on that internal diff causing possible overheating and excessive wear.
--
If at first you don't succeed, you're not cut out for skydiving

"Roy" < snipped-for-privacy@home.net> wrote in message
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diff
with
going
of
spare
use.
It the transfer case has 2WD capability and truly decouples the axles, then he would be fine.
--
If at first you don't succeed, you're not cut out for skydiving
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Roy wrote:

On the Durango I do not have 2WD mode. It's AWD, 4W-Lock and 4W-Lo.
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I was just out with the wife's Envoy and decided to pay attention to things. The knob is labeled 2HI, A4WD, 4HI, 4LO. So I guess I could do it in 2HI and be okay. I'd think that you would be able to in AWD if it didn't sense a slip, Also as Nosey pointed out the difference in size isn't that much. Were it me, I'd do it.
Roy
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at the same time if the axle diff is "open" would the size differance not be taken up in the diff gear set as its only one tire. granted wouldnt want to run missmatched forever on the axle as that would wear the diff gear set. but im with the other poster as long as the axle is "open" i personally dont see why the transfercase would see extra strain.
--
-Chris
05 CTD
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Not like you think. Remember, "open rear" only means that there is nothing forcing the wheels to turn at the same speed, not that they can turn at different speeds with no effect to the axle speed. There is no magic here, if the two wheels are turning at different speeds, then the axle will turn at a speed between them as there is no way for the axle to "take up" the difference in an open rear other than changing speed. This will cause little wear on the spyder gears in an open rear as that is what they are intended to do anyway. If you had a limited slip OTOH, then it would cause added wear on the clutches by causing continuous slippage as it will to the clutch material in the transfer case (if it is using a clutch type coupling). The transfer case sees the same input on an AWD as it does on a PT, it only deals with it in a different way. In a PT system, it really has no way to deal with axles turning at different speeds other than forcing the axles to turn at the same speed causing a wheel to slip which puts excessive strain on the drive train. In an AWD system, it deals with different it by allowing something internal to the transfer case to slip and that causes either wear or heat or both, depending on the type of coupling the transfer case uses.
--
If at first you don't succeed, you're not cut out for skydiving
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additional
I
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turn
nothing
if
They don't take up the difference, they allow the wheels to turn at different speeds by transferring the difference to the carrier otherwise, you are completely correct.

strain
It would not. It would send the same thing to the transfer case, it is the diff itself that would be under greater strain.

forcing
coupling
the
the
not
That is correct. In a turn, the front and rear axles are turning at different speeds which winds up the drive train in a PT system. If a AWD, the transfer case has the ability to release that pressure with internal slippage but it will not be good for it to put it under that condition constantly. Putting a smaller tire on will make the axle it is on turn at a different speed than the other and this will make the transfer case have to deal with that "turn condition" constantly. Now if your vehicle also has a 2WD capability, you can set it to that with your smaller spare and it will probably be fine until you get the tire repaired as long as you leave it in 2WD mode. The way I see it, it's your money, your vehicle, and your choice as to what to do, good luck either way.
--
If at first you don't succeed, you're not cut out for skydiving



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at
the
are
rotational
(as
to
case.
the
really
slip
a
to
a
in
agreed. running the miss matched on any vehicle would need to be only temp. im not the op i was just trying to further understand the concern with the AWD. and i now have a better handle on the concerns involved
The way I see it, it's your money, your vehicle, and your choice

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Mixing different size tires is never a good thing. Other wise the NSTB would not have issue with it nor would the manufacturers. Virtually every manufacturer states in their owners manual states so. It is ok to have all tires the same size but not to have one tire a different size. You can do what you want but it is not prudent for your safety and others around you. Doing so will totally change the handeling charastics of your vehicle especially an SUV. Why do you thing manufacturers have gone to full size spares on SUVs by chance?
My 2 cents Coasty
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"Coasty" <uscg_ret at comcast dot net> wrote in message

turn
magic
will
up"
they
axle
otherwise,
will
with
thus
surfaces.
internal
have
has
it
the
all
all of witch was why i wasnt saying for a full time use. but i wasnt fully understanding the concern for the transfercase in using a smaller spare in temporary situation.
--
-Chris
05 CTD
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Mike, it looks like a few of us need a bit of a education on this. Jump in please.
Roy
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Mike Simmons wrote:

That is why they call it a spare. It's not a drive on it all day tire.
JAM
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