Replace All Four Tires Not Just Two

[Larry Witherspoon]

I have been replacing only front or only rear tires for years

Must have been lucky

Finally caught up with me a couple of weeks ago

Replaced rear tires only but circumference difference from those in front was too great

Strain on rear differential caused failure in about a week driving back and forth to work 30 mile freeway round trip

Don't risk it on all wheel drive Subaru

Cost of differential replacement is much greater than the extra two tires

Only upside was I had bought a limited slip differential some time ago and was having trouble finding somebody who wanted to do the install

Now it's in but with no warranty because I supplied the part and there is fear if gearing is off by one tooth same prob will go down

I think all should be OK

Switched from OEM 3.90 to OEM 3.90 LSD (very rare)

Larry learn the hard way Witherspoon

[SP-Boxer]

Shouldn't be a problem There are more people who believe all four tires must be replaced. We never had any problems here in Europe.

Besides, you replaced there tires on one axle! Then your center diff should be broke en not your rear diff

Or am I missing something?

[entirelyturbo]

Yeah, the center diff should have gotten toasted, not the rear diff.

Unless you replaced one tire on the rear, then yeah.

Running different-wear tires left to right will destroy the rear LSD just as fast as running different-wear tires front to rear will destroy the center LSD.

[Larry Witherspoon]

Maybe I was lucky and lost the rear diff instead of center, or maybe 92 Legacy is set up different somehow. Measured tires and found the newer replaced rear tires were 195 / 65 whereas older retained front tires were 205 / 65. The older front tires were 79 inches (200.7 cm) circumference. The newer rear tires were 77-1/2 inches (196.8 cm) circumference. The 1-1/2 inch (3.9 cm) difference in circumference translates into a height diff of about 1//2 inch (1.3 cm). Anyway, I guess it's that 1-1/2 inches further the fronts were going than the rears for every revolution that did it to the rear diff. When I drove away with the newer tires I immediately noticed a funny vibration like I had those big knobby tires on but I thought it was because the new tires had a rotation direction specified which was new to me. It was the diff gears straining tooth against tooth. I never had any probs either after years of replacing front or rear only but probably never had a circumference difference so great.

[evolutionmovement]

It's not gears, it's either a viscous fluid or clutch packs depending on manual or auto. The rear LSD is a viscous set up. The different tires cause a difference in rotational speeds between the shafts from the respective sides. A constant change in speed wears the diff in question out through overheating.

[Radial GT1]

It all sounds horrible. I need to throw away my leaky rims. Always have tires that are going flat.