Tread depth difference in tires

tires

#1

My tire place told me to buy four new ones when one of the tires had an un-reparable flat. Other three were at 8/32, a new one will be at 10/32. Does this really matter? When the car sits on the tires, the effective radius (distance from the road to the center of the wheel) will be less than when the tire is not carrying any load. Isn’t this correct? So if I buy one new tire, and inflate the other three to a higher PSI, won’t they all have a same effective radius? Will this cause any other problems?


#2

I don’t think the tread difference of 1/16 is enough to worry about, even with AWD (which I assume you have). Inflate them to the correct pressure and drive.

PS, I assume the new tire is the same model as the other 3? If not, then things get interesting.

If you don’t have AWD, even less to worry about.


#3

I have a 4WD. I run on 2x4 most of the time.


#4

I’m certain 1/16" (difference) is OK, and that 1/4" is probably too much, but where is the dividing line? It does depend upon drive line. AWD is most sensitive. FWD probably next sensitive (and you only have to worry about differences side-to-side). RWD about the same. 4WD is not engaged in dry highway conditions, so it becomes same as RWD.

Comments? Corrections?


#5

My tires are all the same brand model and specs, including the new replacement tire. I have a 2001 Nissan xterra 4x4. It’s a RWD when in 2WD mode. The new tire and an old tire are currently in the front.


#6

I would be MORE concerned that the treads matched, as close as possible, ideally same brand/model…otherwise, not a big deal.


#7

That’s correct Bill.

That is also the reason I don’t buy awd vehicles as good as they may be (in adverse conditions). Transfer cases are very expensive to fix or replace.


#8

Since you don’t have AWD, I would suggest replacing two tyres and putting the new ones on the back. But be sure not to engage the 4WD on dry roads. BTW I would suggest putting the best two on the back for a FWD as well. Having better tyres on the front can cause serious handling problems in emergency handling conditions.

NOTE: you should check your owner’s manual. If there is a special problem for your vehicle it should be indicated there and will likely indicate the maximum allowable difference in circumference. Do not violate those instructions.


#9

there is only 1/16" difference, I don’t think it makes a difference where he puts them.


#10

I assume AWD? Even with Subaru AWD replace the single tire with SAME make/model/size. My guess is tire shop does not have your single tire.

Do not replace with a different model tire within make or make/model. The diameters vary model to model despite same labeled size.


#11

read the posts. It is 4WD and all the tires are same model, incl the replacement.


#12

The difference isn’t great enough to cause a problem with the differentials, but it might make the alignment feel off, that is it may pull a little to one side, but not much. Changing air pressure will only change the height to the center of the wheel, it won’t change the circumference or effective radius.

You could have the tire shaved down to the same tread depth as the other three. You could ask around to see if your tire store, or another in the area has a similar used tire that was taken off another vehicle for the same reason that your tire shop wants to sell you four new tires. A junk yard may have a similar tire with the right tread depth for a reasonable price.

If you do buy four new tires, look into keeping the other three. You might need one in the future or may be able to sell some of them to others in the same situation. You might try ebay or craigslist for a used tire or to sell your old ones.


#13

I feel his 4 wd would be more forgiving with differences in tread depth…esp if engaged only in slippery conditions. As far as AWD is concerned, differences in tire preasure may account for deflection as great as 1/16 of inch and how many Subaru’s ever need drive train work. Considering the number of miles racked up they seem to be VERY forgiving as well. Mine had well over 200 K W/O problems and there were many times that I wasn’t as festidious as I should have been about tire pressure.


#14

“The difference isn’t great enough to cause a problem with the differentials, but it might make the alignment feel off, that is it may pull a little to one side, but not much. Changing air pressure will only change the height to the center of the wheel, it won’t change the circumference or effective radius.”

That needs further explanation since the height to the center of the wheel is the radius which DOES affect the circumference which with lower pressure does require that wheel to rotate more often hence the pull…


#15

PS If you don’t believe me…check a road grader out…it turns using tire "tilt’ whch effectively changes tire radius on both sides which turns the grader. It uses tilt turning because of the lack of clearance needed for actually turning the wheel.


#16

1/16" is 1/4 of his total current tread.


#17

I could be wrong, I’ve never driven a grader, but I always thought the wheels tilted to compensate for the tendency of an angled blade to push the front end sideways. I thought the front wheels also turned on a vertical axis like normal wheels.


#18

Modern graders actually do both with a selectable conventional and articulating steering depending need.


#19

You’re not wrong…old leaning wheel mechanism does compensate for front end push.
The really old one we use also helps grader turn with limited steering clearance.


#20

sorry not clear that it does both…