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Tire replacement 4-wheel drive

I tried to replace a worn out tire. The other 3 of my tires have 50% tread. The tire shop told me that I had to replace all 4 tires as my vehicle is full-time 4-wheel drive. Make sense or was I ripped off?

Of course it makes sense. But you should do that with any car. If one is already worn and the others are at 50%, you’ve already experienced some lack of rotation or other issues. It will just cost you more to buy back the safety you got away without. Or, look into a used tire. At some point you"ll have to buy 4 new ones regardless and get back to proper rotation and care cycle if that was the problem.

Thought not as safe, you can get away with just purchasing two, both on front or back as my manual for a Rav AWD suggests. These cars are more forgiving in a certain range then some people here would have you believe.
Otherwise, every time you have lower presure in one tire, the drive train would self destruct. Match the treads as
close as possible too for safety. When properly cared for, tires generally last much longer on awd cars than fwd ones for me.
What kind of car do you have? There is some variation in their ability to handle differences too.

How did one tire get worn out if the other three are still at 50 percent?

Installing one new tire could cause damage to the full time 4WD system. Some vehicles are highly susceptible to damage from mismatched tires.

What does the owner’s manual say about this?

If you don’t want to buy four tires you could have the new tire shaved to match the other three.

Why did you buy a 4-wheel drive car? I suspect you wanted safety and snow/dirt road/ice drivability. That requires four good matched tyres.

Your tyre shop was right.  The tyres need to match or you risk handing and mechanical problems. 

 That is just part of the cost of 4-Wheel Drive cars.

CHECK CHECK CHECK—THERE MUST BE A REASON FOR JUST ONE TIRE TO BE WORN SO MUCH MORE THAN THE OTHERS. Is this the tire shop that you usually go to or did you just pick for conveniance. did you ask several places or just the one. was it just a tire shop or did they do other work also. do you check the pressure in your tires weekly, monthly, or never. your tag says it is a mercedes, if you have a warrenty, get it checked out.

"That is just part of the cost of 4-Wheel Drive cars. "
“Installing one new tire could cause damage to the full time 4WD system.”

With all due respect, I think we are over stating the situation, time and time again. Through my own experience and talking with relatives who work in service departments at Subaru and Toyota dealerships, I feel this is closer to the truth. The cost in tires of owning a modern awd is less than that of a traditional fwd car if both car’s tires are rotated properly and driven the same. The change of torque from front to back (as much as 90%) during accelerating and turning at the same time in an awd, puts it at a huge advantage over fwd cars. The wear patterns generated can never be mitigated with ordinary rotations they vary so much with the rear in fwd cars. In over 20 years of driving these things (awd/4wd cars/trucks) and fwd cars in the same time frame, I have never failed to get more miles(thus saving money) out of their tires.

Secondly; If tire wear difference of 50% or less is the only variable and not improper use and maintenance and you suffer drive train damage from this slight difference in wear diameter; you need to buy yourself a different AWD car. The car you have would suffer damage from much greater variances due to improper tire pressures, rough roads, rotational circumferences differences due to improper weight distribution and general driving winding roads every day. It is just one added factor that may not or may be significant if others are involved, especially poor maintenance. If you change actual tire size where difference is much greater, or mount chains improperly, yes of course. If you maintain a much more significant wear difference for many thousands of miles, perhaps like bald and new, which is unlikely.

Remember there is an open diff between the two rear wheels(and front of fwd car) that is open to the same wear difference in putting one new tire on the rear axle of a rwd truck. So caution everyone about that factor as well and that they could fail at any time when this is practiced as well.

When poor, we all did things like that. I’m not promoting it, as it is unsafe traction wise, and more so during acceleration with awd which could be the real culprit. But please put things in perspective and don’t put the onus on awd cars alone for proper tire purchase and tire maintenance.

Please note; the OP has not yet replied.

ferrari-dreamer already paid to have four new tires installed.

He or she just wanted to know if this was a rip-off.

We can argue this till the cows come home, but the OP is gone.

And that’s not a problem as long as we don’t get into the same old advice that brow beats people into thinking that awd is ungodly expensive to buy, unreliable, expensive to maintain both in tires and otherwise and offers little in advantage over fwd cars. All of which is not true but keeps popping up with every question concerning awd cars.

So what advice should we offer? Should we ignore the problems folks have had with AWD systems when odd tires were applied? Should we tell them to look in their owners manuals for definitive advice when some owners manuals don’t say anything at all - even though they should?

I’m inclined to tell folks that they should be rotating tires on a regular basis AND that AWD and 4X4’s need to have tires of the same size, the same make, the same model, and same state of wear. That way I am ALWAYS giving advice that avoids problems. Remember, the more complicated the advice, the less likely it is to be remembered!

Absolutely, that’s good advice and I don’t question it. It’s always the added statements that just aren’t true. But I’m inclined to always add that whatever advice we give to awd cars for tires is the same as for any car. I indicated the statements I disagreed with in previous post. Generally speaking drive train problems coincide with the overall reliability of car makes regardless of it’s system. Check the CR surveys.

PS; Neighbor’s son recently confided to me when plowing with his dad’s 3/4 ton truck on snow over ice, he used his mothers Subaru with studded tires to pull it out of the ditch when it slid in. He hooks the chain onto a front suspension component (only thing available) and pulls backward to help get it out. I suspect some thing may break soon. He might blame it on “improper wear or miss matched tires” though so his dad won’t find out the real cause. I assume dad doesn’t read this forum and will blame the failure prone awd systems of Subarus.