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.
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
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
Ditto. Any odd sizing of tires on 4WD or AWD will cause additional drivetrain stress and must be avoided.
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.
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
It will not help the drivetrain to do this. The little bit of money you save here can cost you big $$$$$$ down the road in excessive wear in the transfer case components.
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.
Okay I'm learning. What if the transfer case is not in awd? This is a spare tire that is just to get him out of the mess he's in, not for everyday use.
Roy
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.
Mike, it looks like a few of us need a bit of a education on this. Jump in please.
Roy
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.
It the transfer case has 2WD capability and truly decouples the axles, then he would be fine.
agreed. the spyder gears are inteneded to take up differance in rotational speed between 2 wheels on the same axle during a turn. thus they do nothing while in straightline mode. running 2 diff tire sizes on the same axle essentially puts the axle's differentail in a continuous turning mode (as if it was in a constant corner)
If you had a limited slip OTOH, then it would cause
yes exactly my point in a limited slip or locker i can see where the strain of the tire size differance would send extra strain to the transfer case.
The transfer case sees the same input on an AWD as it does on a
ok. AWD is i diff animal than anything ive worked on in the past. transmission/transfer case was not my specialty. but i understand about the transfer case not having the ability to diff between drive shafts, thus the reason for the ole rule of use 4 wheel only on slippery/muddy surfaces. not hard paved surfaces. correct me if im wrong here.
now all that being said im sure there are points im just not privi on, along with system differances ect ect.
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.
It would not. It would send the same thing to the transfer case, it is the diff itself that would be under greater strain.
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.
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
That is why they call it a spare. It's not a drive on it all day tire.
JAM
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
While I agree that running mixed tire sizes on a AWD or 4 wheel drive is a bad thing, these two particular tire sizes are so close in diameter that it will do no harm. The stock tire size will roll 661 times in a mile. The new tire size will roll 660 times. That is only one tire revolution difference in a full mile. This will cause your vehicle no harm.
On the Durango I do not have 2WD mode. It's AWD, 4W-Lock and 4W-Lo.
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