Jump to content

Drivelines and Tire Replacement


Recommended Posts

Hi Everybody,


got a question...


I've been told by the dealer that tire replacement on my 05' Legacy 2.5i, and because of the Driveline, they say all four tires have to be replaced together and tire pressure needs to be monitored constantly to insure proper inflation in all four tires.


Now through research I was able to find out that the new driveline is a 45/55, power and torque split... (45 front/ 55rear). The dealer says that power is applied to all four all the time and if replacement isn't in fours driveline binding can occur.:eek:


I have no experience with subaru's, this is my first one, but I know that 4x4's with locking diffs it's the same way. four tires at a time.

I've been to dealers that will tell you anything to get more money from you. But I have no reason to doubt the Suby Dealer.


anyone have any experience with this?



Link to comment
Share on other sites

yeah its true. I noticed my front tires were hella bald, and my rears were fine (at least 50% life left), and I started hearing noises. I thought it was the tires, so I changed em, thought it was balancing, so I had them rebalanced (free of course), I even went to the dealer, and they said, "Yeah, with fron tires being bald and rears fine, that WILL cause a prob." They wouldnt lie to me, cuz they were gonna fix it under warranty anyways. So I brought them for a ride, they couldnt hear it. They put it up on the lift, and drive it to listen under the car. It was an exhaust leak from removing my resonator and having a shop weld a straight pipe in, lol.


So yeah, it wasnt the prob I had, but it DEFINATELY CAN cause problems. My tranny seems fine though. The sound I heard at 50mph and above changed tones/quited down some when I fixed the leak. It sounded like the center diff though, so I was freaked out.

Link to comment
Share on other sites



On All-Wheel Drive (AWD) vehicles, it is extremely important that the rolling or outer circumferences of the tires be within 1/4 inch of each other. This means that you must physically measure the size of the tire. This is best done with the weight of the vehicle off the tire and at the tread centerline. Also be certain that the tires are properly inflated since this can affect your readings.


If you need to replace just one tire, the same holds true. The measured difference in circumference between the replacement tire and the other tires on the vehicle cannot exceed 1/4 inch.


Depending on the vehicle mileage, it might be better to replace all four tires.


If the vehicle mileage is low and the tires have been rotated and driven at the proper inflation pressures, then you may be within the allowable 1/4-inch difference in circumference.


If the difference between the new/replacement tire and the current tires is within this 1/4-inch maximum, then the tire should be compatible. If it is not, then other tires will need to be replaced to conform to the 1/4-inch rule.


Exceeding this 1/4-inch difference in tire circumference can place unnecessary wear on drivetrain components, possibly causing them to wear out prematurely.


This is a pretty tight specification. The Bridgestone 225/55 r17 RE92A has an overall diameter (unloaded) of 26.9 inches. This yields a circumference (2xPi x R, or Pi x D) of 84.47" (rounded from 84.466).


If we add or subtract .25" to the circumference, we wind up with a minimum diameter of 26.82 (= radius of 13.41). That's a tread depth difference of 1/2 that, or 0.04".


Tread depth is usually measured in 1/32" in the US and the Impotenza has a tread depth of 10/32. 1/32" = 0.0313". So much over 1/32" difference puts you outside the spec.


The Bridgestone site says the 225/55 r 17 turns 775 revolutions per mile. But if you use the calculated radius, you get 750 rpms. I want my 25 rpms back.....

Who Dares Wins


Link to comment
Share on other sites


This topic is now archived and is closed to further replies.

  • Create New...

Important Information

Terms of Use