Had to unexpectedly replace all four tires today. Drove about 175 miles, pulled over to take a break and double check the lug nuts. Turns out three tires are one model of firestone tire and the fourth is another firestone tire. They are all the same size at 205 70r 15.. Any thoughts on the severity of this? This is on a 96 outback with 5 speed transmission and 203K miles. I have to call the shop back tomorrow to see what I can do about it but am concerned about the miamatched tires even if I get new ones. They are all season tires according to tire rack but the different on has a m+s rating on the sidewall too. I guess I can measure the diameters. I'm just kind of annoyed right now.

Edited September 24, 201312 yr by goof_ball

the specific brand of tire or even the tire model shouldnt matter so long as there all the same size 

it doesn't matter.  keep rolling.

 

they're all the same size.  sure - check tread diameter if you want - i wouldn't waste my time as i've been around Subaru's long enough to know it won't matter.

 

You can put completely different brand/tread on there and it won't matter.  if slight variations in tires (other than size/circumference) could blow up your transmission then that assumes some kind of resistance/weight/inertia difference causes issues - you'd have to worry about different amounts of grease in the DOJ's, the CV band clamps being different weights, axles being different weights, rocks stuck in the tread, mud or snow caked in the rim making them weigh different amounts....subaru transmissions would be blowing up all the time based on the way some people talk about tires on Subarus.  

 

there are tire shops around here that install two new tires on subarus - one on the front and one on the opposite side rear.  i'm not saying i recommend that or think it's a good idea and i've never done it...but apparently it is suggested that due to the way open differentials work (only one tire in the rear and one tire in the front is actually driven by the trans), it's possible to do that.

 

get a FWD car stuck - only one tire spins - that's why FWD tires don't need to match even up front.

get a 4WD Subaru (without rear LSD or VDC or DCCD - none of which yours has stock) stuck and how many tires spin - 2.

Edited September 24, 201312 yr by grossgary

Tire size is kinda relative depending on tread depth and what the manufacturer decides is going to be the size of the mould for that particular model of tire. The general rule is that they will be close, but there are differences in diameter between tire models even of the same written dimension.

 

Good news is 200 miles of wear isnt anywhere near enough to cause damage to the drivetrain, or cause enough tread wear of the new tires to affect overall circumference (probably still has the "nubs" on the tread). And that oddball tire is probably within the 1/4" max. difference in circumference allowed by Subaru.

 

Not to say you should keep that tire, traction temp and tread wear ratings of that tire may be different than the other 3, and even if they aren't significantly different the tread design and rubber compound could cause that tire to have different traction characteristics which could cause some issues when you need to make a panic stop, or just drive across town in the rain.

 

Point it out, and make sure the shop puts the correct tire on the car.

It will be fine. IF you had 2 pairs of different tires, then there could be a rotational difference across the center diff. Theoretically you can run one size on one side of the car, and another size on the other side, or diagonal. The odd duck tire is best suited to the rear.

On my first Subie, a 91 Leggie with AWD, I didn't know anything about matching tire size, or tread depth difference. I drove the car with different brand tires and tread differences for over 100K miles, and never had a problem. So, my advise is to not worry about it.

 

Point it out, and make sure the shop puts the correct tire on the car

 

short term there will be no problems.

 

but i would not drive with it long trerm.

 

subaru is very specific about the circumference of the tires on an AWD car.

 

make them correct the issue.