I never heard this before

I had to help a neighbor remove the rear tire off his 2014 Dodge Ram 1500 4X4 due to a detroyed rear tire from road debris.

He took the tire to well known tire shop in our city. They convinced him that he needed a new tire which he bought. When he

got back home and I checked to see if he needed help mounting it. he told me that the tire shop told him that since he had a 4 wheel drive, he would need 3 more new tires to balance the torque . I could see maybe SOME logic if the the other 3 tires were completely worn out, but they are not. It sounds like somebody may be pushing this a little too much. Am I wrong, or ? (they told him to just use 2 wheel drive until he could back there tomorrow night.)

 

Tires on the same drive axle need to be the same size. If one is worn a lot more there might be the a difference in circumference that could cause a problem. Never hear of having to change all 4 tires because of this. I have heard of differential problems from different tires on same axle.

 

Look in your owners manual, it will likely mention it if it is required to change them in pairs or in sets of 4.

 

If you take a new tire and roll it on the ground 1 rotation and measure how far it went say 3 feet, then do the same thing with tires 1/4 in shorter and roll them out 1 rotation it will not be quite as far, not a huge difference but a difference, if you sawp out the drivers together its ok cause the steering wheels are not locked into the rear axles, in 4 wd you are however in 4 wd you should be on dirt that allows some slipping
Its like having lockers on the axles, if you engage front lockers and try to turn it wont want to turn so well unless you unlock the lockers, on street I have seen rear ends that clicked and tires chirped as one spins faster than the other tire, unless it will go awd on asphalt I dont think all 4 tires have to be new or equal in diameter, but as far as having 2 sizes on the driver axle with one tire continuously spinning a tiny bit faster this could cause heat and wear if driving fast and for long durations, I would ask the dealer to make sure its ok or not, but theoretically there is a point.

 

it makes sense to me too, to equalize the tire diameters on the same axle. If a small difference (in tire size) is critical, he has an unused spare he could bring down and use on the opposite side of the axle from the new tire he had to buy. How much difference in tire diameter is critical in this scenario? It sure bugs me on the other part of it. (having to buy all four tires) I might talk to somebody's boss about that!

 

Ok if you have two tires on the back axle the same diameter, and two tires on the front axle the same diameter (but different in diameter from the two on the rear), how much difference in tire diameter is critical?

 

4 tires, no way, 2 tires on the same rear axle, well maybe.

WSS a vehicle checking for wheel speed etc could see the difference as a slip event and attempt to correct with ABS but suspect the tire would have to be at the extremes if sizes to occur.

If other tires are in "good" condition I would run em!

Same logic for a vehicle with full time AWD.

 

I've been running 4 wheel drives for 26 yrs and I've always heard you should have 4 matching tires. The main thing is for all 4 tires to be the same size! Different size tires will cause parts to wear prematurely but there is a little wiggle room. I wouldn't be afraid to have 1 new tire and 3 older tires as long as the old ones still had a lot of life left.

 

It would be interesting to know the age of the service guy at the garage who told this to your neighbor. If he was older and seasoned he would most likely say you're OK with a slightly worn tire on one side. But if he was young, I'll bet he would say change all four! Just say'n.

 

While I was still working as a mechanic We had a memo come down that on 4 wheel drive we could not just replace 1 tire on drive axle of 4 wheel drive vehicles. This was after several major repairs of differentials.

 

My old man worked at a Subaru dealership for a while and their practice was the tires all had to be within 1/8" diameter of each other.

 

That ⅛" diameter tolerance is a worthy contribution.

Another technique is to use a calculator to estimate revolutions per mile for different tire sizes to make sure that they're similar or at least comparable. Many tire sales organizations and manufacturers offer such a calculator; but here's one that seems to be at arm's length from any specific brand or retailer:

https://tiresize.com/calculator/

After working with such a calculator for a while, you can then get fancy and start adjusting the dimensions to account for perceived differences in the wear of individual tires.

 

Still wondering what/if your owners manual has anything to say on the topic. If they do, all this talk is pointless.

 

I have a truck and I usually replace just one tire at at a time. I don't replace the tire unless it needs it. Never had a problem.

Good idea to check the owner manual like someone said also. I guesstimated on a maintenance procedure for years before I finally discovered the answer in the owner manual!

But all these guys are more experienced than me. Safety is first and foremost with cost savings in mind also.

 

When you are in 4 wheel drive you need all 4 tires to be the same size so you don't put undue stress on axles/differentials. IMO there is a small amount of wiggle room just like there is on the drive axle of a 2 wheel drive.

 

Good point.........want to avoid premature wear and tear from undue stress

 

The owners manual says to replace tires in pairs per axle. That would predicate rotating them on recommended schedule to keep things balanced IMO