4WD & Tire Question

[Mother]

if it is open diffs and a true 4x4 and not an all wheel drive with a 4x4 lock (like on the newer fords) then just by 1 tire. you may wear them a touch faster but you won't hurt anything. 

[Mother]

Now for my disclaimer. All I know is standard part-time chain and gear drven tranfercases with a planetary gear set, your basic rear wheel drive with a disconected front drive axle.

Anything fancy like a hummer/subaru/newer ford then I would just sell back the 3 and buy 4 new ones.

[Porsche Monkey]

Just get the one tire unless you have a limited slip of any kind in that thing. This tire guy is full of shit.

[ducatiz]

utter bullshit

replace the tires on the same axle, that's all you need..

[Howie]

On some late model full time 4 wheel drive vehicles perfectly matched tires are a must.  Yours is not one of them.  If you are anal, replace the two on that axle.  If not, just replace one.

[Porsche Monkey]

On some late model full time 4 wheel drive vehicles perfectly matched tires are a must.  Yours is not one of them.  If you are anal, replace the two on that axle.  If not, just replace one.

Agreed

[Smokescreen]

A few years ago I was in a snowstorm on my way down from Denver to Colorado Springs.  The owner of the Subaru I was riding in got spooked when the Nissan Murano immediately ahead of us suddenly spun into the median.  She pulled over and refused to go any further.  When we both got out to walk around and switch seats, we were having to hold onto the car to not fall on our asses. 

So I took off (not quickly) and the car was all over the place.  I realized she'd had it in 2WD the whole time.  On a Subaru, that means FWD which is nice.  This was an older Loyal so it had an engagement stick tx instead of the full time stuff we see now.  As it was shift on the fly and I was only doing like 15MPH  I went ahead and shifted into AWD.  Things got even hairier.  The front and rear weren't working together and it seemed like the viscus coupling (Subaru and Audi used these as a kind of limited slip) was forcibly disconnecting and reconnecting.  It was seriously unnerving.  I ended up shifting back into FWD as the car was more manageable that way. 

When we got home, I told Sue to take in her car and have the system looked at.  Something was not right, I said, the car can't use AWD. 

Ends up she'd replaced the front two tyres, and the difference caused the AWD system to fail due to the fact that the CD spins the front and rear at the same rate, requiring the tyres to be the same size.  So the front was pulling the loaded rear and forcing a viscus disconnect, even on a road that was soo slippery I couldn't walk down it.  There were crashes every mile.

Moral of the story is, if you have different diameter tyres on the front than the rear, YOU DO deplete the function of your drivetrain and make it all but useless in 4WD ON ROAD.  The question then becomes, does that matter to you?  Do you use 4WD on road?

This is actually a sort of funny read on here, as I'm pretty sure these same respondents would clammer to tell you you shouldn't just replace one tyre on a bike.....  But to refute all the shenanigans claims, I can tell you from first hand experience that using different diameter (even older and newer) tyres ON ROAD can do damage to your driveline that will make tyre replacement seem inexpensive. 

All the same, were it me, I'd only replace two.  Then all four when the oldies wear out, and keep the newer two as spares.  But I, despite living in Colorado Springs, am unlikely to use 4WD on the road this late in the season.

[ducatiz]

Ends up she'd replaced the front two tyres, and the difference caused the AWD system to fail due to the fact that the CD spins the front and rear at the same rate, requiring the tyres to be the same size.  So the front was pulling the loaded rear and forcing a viscus disconnect, even on a road that was soo slippery I couldn't walk down it.  There were crashes every mile.

different size tires?  of course it was weird. 

[Mother]

and

it was in one of those fancy subaru systems.

not a standard 4x4

also

I am one of those that will run a front through 2 or 3 rears

:-)

[Smokescreen]

different size tires?  of course it was weird. 

No, the same make and model tyre, just newer, as she'd got in the habit of replacing one end then another as it wore out. 

Mother- the "fancy" Subaru system on the Loyal is a transfer case with a center viscus diff.  Not dissimilar (save for the center viscus diff) to the systems used on any other vehicle with a lever opp transfer case.  So in this case, the only difference between the Loyal and a standard 4X4 would be the transfer case going FWD instead of RWD in 2W mode. 

While on my CJ7's Dana 300 transfer case I wouldn't even think twice about beating the hell out of it (I used to leave the hubs engaged despite the Detroit locker in front), and I'm sure Nissan uses plenty durable parts, I still hold to it being a bad idea if you plan to use 4WD on road.  This is doubly true if the ExTerra is outfitted with any kind of dynamic vehicle control, which will be continuously monitoring wheelspin on each corner and will react to varying wheel speeds in a straight line and in turns.

My ExTerra experience was limited to two long term magazine ExTerras, but the last one I drove was tempermental about tranfer case activity at the best of times. 

You know the saying, "oil's cheaper than parts"? this is one of those times.  Tyres are cheaper than hard parts.  Though I suppose only Triple J will be responsible for the cost of failure in this case.  It's not like it'd cause an accident.  Just possible damage to parts.

Like I said, I'd replace two and avoid 4WD on roads.

[ducatiz]

No, the same make and model tyre, just newer, as she'd got in the habit of replacing one end then another as it wore out. 

yeah, i am surprised most ppl don't know you are supposed to rotate about every 6-8 k miles

the warranty on most tires requires you to rotate and to record it.  we got new Toyos on the wife's car and one developed a bulge.  i called them for warranty replacement and the first thing the girl asked was "do you have the rotation records? "

YES I DO.

[the_Journeyman]

I know to do that.  Every other oil change the tires get rotated ~

JM

[Smokescreen]

It's an easy thing to forget.  I rotated my Jeep's tyres regularly, because they never wore evenly (fr v. r) but with my WRX I only did front to rear rotations.  Not the crossways bit.  The WRX wore pretty evenly from side to side.

[Triple J]

Thanks for all the input. 

I'm gonna get two and put them on the front (where the flat is anyway). I'll just leave them there until Fall...so they'll probably be about the same wear as the rears (or at least a lot closer) when it's possibly time for 4WD in the snow again. My Xterra definitely eats fronts faster than rears. I do use 4WD on the road when it snows, so if it feels like there is a problem then I'll buy all new ones and consider it a lesson learned.

BTW...it's an '04 Xterra...it doesn't have any fancy electronic driving aids like traction control, stability control, etc. I've also never had a problem at all with the T-case.

I always replace 4 tires at a time, but damn...these are only a year old!

[Sinister]

if it is open diffs and a true 4x4 and not an all wheel drive with a 4x4 lock (like on the newer fords) then just by 1 tire. you may wear them a touch faster but you won't hurt anything. 

Dumb question alert:  How does one know if one has open differentials?  (I have an '01 Chevy Silverado Z71)