Tires & Xmission Damage..Myth or Fact

[jib]

There is a very simple solution folks. Rotate your tires regularly so they will all be the same size.

 

 

When you have that flat which requires replacement tire replacement, buy the new tire and have it mounted. Drive to your nearest racing/tire shop that has the capability to shave a tire. For a few dollars and 30 minutes, they will remove tread from that new tire until it is sized the same as your other tires.

 

 

Non-issue.

 

 

Jack

[nipper]

A few things here:

First off the front differential in a turn turns faster then the rear differential. This is the need for some sort of differntional or or dissconnect in the center of the car.

The center differential can be a viscous coupling (some have manual locks). This is a bunch of discs with holes in them and filled with silicon fluid. As the speed misnatches, the fluid is sheered, and this creates friction, which creates heat. Heat causes the fluid to get thick (one of the odd properties of silicon fluid) and causes the center differential to move as one. These differntials are calbrated to allow slip as in turns for short times. There are center differntials with clutch packs like automatic transmissions, and a computer decides to do what when. Then there is the good old second lever sticking out of the floor kind, where it is just another gear box.

All these systems are sensative to mismatched tires, within the tires specs (meaning the tread life). The viscous coupling is most sensative to this action. This is also why heat is very bad for it. An over heated viscous coupling will lock up the drivetrain into 4wd.

The clutch pack system depending upon design may not care. The manual system wont care untill you have it in 4wd and on a straight line you will immediatly notice it. The viscous coupling will care as the miles add up and the differnce in speeds slowly raises the temp of the fluid. If all you do is drive around town, you may never see this happening.

It is highly recomended that you stay within the same tire faimly (meaning same series all the way around be it 70 or 75 or 85). As far as i know, subarus are biased towards the front, meaning in 2wd they are front wheel drive cars, or most the power goes to the front at all times. New tires should go on the front. This will slow down the front differential speed. I think the newwer subies now use a computer to control the AWD, but it still applies.

ALWAYS ROATATE TIRES ON AN AWD VEHICAL.

There is amount of allowance for diffrent rotational speed in the system, but all you need is one tire down 5psi of air, ir with a slow leak, then add in 2 new tires on an axle, you are starting to ask for trouble.

Also if you have a limited slip differential it is IMPORTANT that both tires on the same axle match.

You can wipe out tires, bearings, the driveshaft, carrier bearings, transmission mounts, transfer case (center differntial).

 

Which leads us to the question, why for not get a 300.00-400.00 set of tires vs. a 1500.00 or more repair (and still have to get a set of new tires after that.