Different tread depth tires paired on same left/right side vs same axle?

[MC Hammered]

I have a set of Bridgestone Blizzaks i was considering to use on my 1996 5MT Outback.

2 tires measure out at 10/32 the other 2 at 7/32, from the digging I have found this is outside of the Subaru 2/32 spec but I will take my chances.

I was thinking of running matched pairs on the same axle with the 10/32 pair on the front, but have read advice saying "run the new tires on one side and the old tires on the other side" but this is puzzling to me.

Can anyone explain why the left/right mounting arrangement is better than a matched axle setup?

[1 Lucky Texan]

if you have open diffs, there should be no torque bind putting one 'small' tire in the front, and one 'small tire in the rear. (they can be diagonal or on the same side)

this assumes the 2 'small' tires are the same circumference.

it still is not an ideal situation.

[subaruserviceguy]

Originally Posted by 1 Lucky Texan

if you have open diffs, there should be no torque bind putting one 'small' tire in the front, and one 'small tire in the rear. (they can be diagonal or on the same side)

this assumes the 2 'small' tires are the same circumference.

it still is not an ideal situation.

This is correct as long as you do not have the limited slip you are ok with the tread difference. You should keep the like depts on the same axle. But I agree it is not the ideal situation. Just make sure you if you are putting snow tires on that you are putting 4 of them on not just 2.

[John E Davies]

I would call around and see if you can find a shop that will shave those bigger tires down to match the smaller ones. The machines aren't used much these days, but a tire recapper should have one.

John Davies
Spokane WA USA

[canubaru]

3/32 is probably out of spec, but the actual spec is ABOUT 1/4'' in circumference. so get a 10 ft. metal tape and measure the circumference. 2/32 is a close estimate for most tires. but smaller tires (96 obs) will have a larger tread depth tolerance than larger tires (03 obw). (for your tire 5/64 is probably closer assuming it is the stock size.)

tirerack.com will sell shaved tires.

measure the circumference and see. if it is close i would probably run them.

EDIT: according to my math the difference is going to be a hair less than 5/16 inch. if so, i would run them on the front till the wear down. this ASSUMES the tires are 185/70/14 and they actually ARE those dimensions. which, of course, they are not, but check.

[MC Hammered]

Originally Posted by 1 Lucky Texan

if you have open diffs, there should be no torque bind putting one 'small' tire in the front, and one 'small tire in the rear. (they can be diagonal or on the same side)

this assumes the 2 'small' tires are the same circumference.

it still is not an ideal situation.

Originally Posted by subaruserviceguy

This is correct as long as you do not have the limited slip you are ok with the tread difference. You should keep the like depts on the same axle. But I agree it is not the ideal situation. Just make sure you if you are putting snow tires on that you are putting 4 of them on not just 2.

AFAIK my 96 does not have a LSD and I will be installing 4 snow tires which came from my FWD car I had last year. The tires with the wear were on the front axle.

Originally Posted by canubaru

3/32 is probably out of spec, but the actual spec is ABOUT 1/4'' in circumference. so get a 10 ft. metal tape and measure the circumference. 2/32 is a close estimate for most tires. but smaller tires (96 obs) will have a larger tread depth tolerance than larger tires (03 obw). (for your tire 5/64 is probably closer assuming it is the stock size.)

tirerack.com will sell shaved tires.

measure the circumference and see. if it is close i would probably run them.

EDIT: according to my math the difference is going to be a hair less than 5/16 inch. if so, i would run them on the front till the wear down. this ASSUMES the tires are 185/70/14 and they actually ARE those dimensions. which, of course, they are not, but check.

The Blizzaks are 195/60/15.

I just measured all of them with a tape measure and the 10/32 pair are 76" circumference and the 7/32 pair are 75.25" so a difference of 0.75"

I am surprised at how much difference there is from only 4 months of use.

Guess I will have to sell the two worn tires and get new ones or sell all of them and get replacements.

[plain OM]

Originally Posted by MC Hammered

. . . I just measured all of them with a tape measure and the 10/32 pair are 76" circumference and the 7/32 pair are 75.25" so a difference of 0.75"

I am surprised at how much difference there is from only 4 months of use.. . .

The originally measured 3/32-inch difference in radius equates to 0.6 inch difference in circumference.

See the calculator at: Area, Radius, Diameter, Circumference; plug the 3/32 difference in tread depth (.09375) into the Radius block, and select Solve Others. This is close enough to the measured 0.75 inch difference for a "no go" determination.

A difference of only 1.27/32-inch in tread depth equates to a 1/4-inch difference in circumference. 2/32 is an outside limit.

That is a large difference in wear if all four tires were on the same car for 4 months. Any idea if the two more worn tires were both fronts, or both rears?

[MC Hammered]

The two more worn tires were used on the front wheels of a VW Jetta.

[Rontalvos]

People say to match the tires to each size of the car because of the AWD. If it was a F or RWD car you would want to match per axle, but having dissimilarly sized tires on the front and back is going to have each axle having a slightly different road speed, and then the center diff will be working harder to even out the speeds between the two.

With front/rear mismatch one axle is being forced to turn faster than the other, whereas side/side mismatch, the differentials are already designed to allow them to rotate faster or slower than the others because of cornering.

[rasterman]

Originally Posted by MC Hammered

I am surprised at how much difference there is from only 4 months of use.

Winter rubber is very soft, wears fast. And last winter was a dud. Whether it snowed much near you or not, it was warmer, and higher roadway temps eat these tires.