replace one tire? all four?

[min]

I have heard that with AWD, when you need to replace one tire, you need to replace all four. I have 4 tires with rims. One tire has a bubble, but I have another tire that could be put on the rim. The tread is all the same, maybe a bit more on the spare. They will all need replaced next summer. Just got the SVX this week and am truly not well-versed. Any suggestions? Also, the SVX must take 91 octane. Years ago, when I owned my first Saab, it also took 91, but I was told, way back then, that you could go 50% 89 and 50% 93 and it would be equal to 91 octane. Is that true in this new millenium??

[$ gest24 $]

Replaceing the tires is kinda critical witht he AWD. If the tread depths are all the same on the tires you have swap out the spare. But if you have to replace on tire with a brand new one, you should atleast do a pair or you'll run risks of messing up your AWD system.

Premium is your best bet in this car, you could run mid grade and some 93. But in the long run, straight up 93 is your best bet. I personally use Shell V-power or Chevron with Techtron to keep everything clean.

[dannmarr]

You should replace them in pairs. Use the extra used tire as an emergency spare for the remaining two on the car. Put the new tires in the front.

[ensteele]

It has been a long time suggestion that all 4 should be replaced at the same time. At the very least, 2 at a time and then inflate the tires so they have the same measurement from top of wheel to the ground.

[huck369]

Take a flat tape, and measure the Circumfrance ( AROUND the tires, the way they roll), after they're mounted and inflated...if they are with-in 1/4" of each other, Subaru sayes you can use them, if more than 1/4", you will ruin your transmission (or diffs)


4 tires now is way cheaper than a new transmission in a few months

[DanSVX94]

I think it's a good idea to get 4 new matching tires. It will help with tire rotations, and you will at some point have to replace the others anyway.

[dcarrb]

Originally Posted by min

Also, the SVX must take 91 octane. Years ago, when I owned my first Saab, it also took 91, but I was told, way back then, that you could go 50% 89 and 50% 93 and it would be equal to 91 octane. Is that true in this new millenium??

I regularly top-off a tank of premium (93 octane in Ga.) with 3-6 gallons of mid-range (89 octane) or regular (87) with no noticable effect on performance or economy. The savings is modest, but paying for more octane than you need is a waste of nickels and dimes better spent on a bag of pork rinds and can of Co-Cola.

dcb

[Earthworm]

50% of 89 + 50% of 93 = 100% 91

As for the tires, try to keep the tread depth of all the tires within 1mm. Tires with higher depth should be used in front as they will wear faster.

[PaulSVX]

Amen

I had 2 same size but different tires on the back, they were causing a major vibration to the drive trian