Tire replacement on AWD

[Steve McKellop]

I know I've read TSB's or at least tech articles on how replacing 1 or 2 tires in an AWD system can harm the drive train. I'm speaking of problems caused by combining worn & new tires, the difference in diameter. I've looked through TSB after TSB and have come up empty handed. Can anyone produce a more technical reference than the link posted?

 

[S F]

I haven't heard of anyone trashing a transfer case, but I suppose the possibility always exists. I don't think you will find empirical data on this, but rather more recommendations and educated opinions like the one you posted.

 

[scott degroot]

I have replaced alot of transfer cases and had to rebuild alot of front differentials for this exact same reason. The rule of thumb is that if actual measured tire diameter varies more than 1/2" problems can and will occur. It is usually a slow and progressive problem and over time the driver doesn't realize the affect that it is having on the verhicle until often times it is too late. If you must have 2 worn tires and 2 new tires make sure that they are diagonal ...new tires on front left and right rear. This usually isn't a problem as most awd vehicles are open differentials. Doing it this way will make the system believe that the front and rear tires are turning at the same speed and should help avoid any long term damage. Your best bet would still be to buy 4 new tires. FWIW in my experience it seems the the Ford AWD systems have more problems than others when it comes to tire size

 

[Steve McKellop]

Scott, that's what I've heard before form Ford Techs, just haven't found anything in print. Some folks won't believe anything unless it's printed in blood. I answered on another forum pretty much what you said and of course the ney-sayers jumped all over me. I was hoping to find it in print somewhere. The diagonal mounting is a new twist on it to me though.

Thanks,