3 older tires 2 newer tires

Due to un-repairable tires and thanks to America's Tire warranties, I now have 2 brand new ST Maxx tires (235/85/16, 18.5/32 tread) and 3 with about 9/32 tread remaining. 9.5/32 difference.

Should I match front left with rear left (and F.R. with R.R.) and have my spider gears always slowly spinning even when driving in a straight line?

Or should I have front left match with front right (and R.L. with R.R.) and have constant front-to-rear driveshaft differentiation while in 4x4? I drive about 100 miles a month in 4x4 always on dirt.

 

New tires go on the same axle

 

The shops I’ve been going to have been putting the new (pair of) tires on the rear axle.

 

Many reputable tire stores won't sell you less than 4 tires for a 4X4. Especially with that much difference in wear. If it were my truck I'd buy 2 more new tires and try to sell the others to someone else. If you don't you'll never get out of the cycle of having 2 new, and 2 old tires on there.

But if you insist the new tires go on the back. And I'd only operate it in 4X4 in extreme emergencies for as short a distance as possible. You'll essentially have 4.11 gears on the rear axle and 3.73's on the front.

 

This for sure ^ also ALL of them need to be the same size on a 4x4.

 

OP said: " I drive about 100 miles a month in 4x4 always on dirt.".

Put them on the same axle and don't worry about it. Not enough difference to matter.