Hi - can anyone confirm if the 4WD on the Impreza is fussy about the front wheels having the same tread depth as the rears?

I used to have a 4x4 Cavalier Turbo and I was told if I put new tyres on the front I had to put new ones on the rear, to keep the diameters the same other wise it would wind the diff up?

Thanks in advance
Richard

 

Not that bad on a scoob, just change the tyres in pairs on each axle.

If you're worried then rotate the wheels front to rear from time to time.

 

Cheers for the reply!

 

Who told you that?
Was it someone trying to sell you tyres?
If you work out the speed differential due to worn tyres, you find it's minimal. Multiply this speed by the torque due to the diff resistance and you get the heat generated. again, minimal.

john

 

From Subaru.com

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-nch 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.

So, in terms of tread depth, 1/4 inch in circumference is about 1 mm of tread.

 

Sounds like Subaru covering thier ****.

 

I find this very surprising but stand corrected.

John

 

I'm sure they are, but how much leeway is there really ? Certainly that advice seems to be taken very literally in the US, it seems that having a new tire (sorry, tyre) shaved to match the others is quite common.

 

Don't know if this is going to change the point of view, but the spare tyre is slightly larger in circumference and by its very nature does not wear down alot, I know you are only supposed to travel at a maximum of 50mph for and hour if i remember right.