Incorrect Tire Size = Differential or Tranny Problems?

[justben]

I won some wheels and tires on eBay for a good price. I was going to install them on my x5 01 3.0i, but they have 275/45-20 and 285/50-20 tires on the front and back. (they are 20x9 and 10.5 Asa wheels). I was hoping not to have to buy new tires immediately, but am concerned that using such big tires in the back will lead to serious transmission issues. I was going to get 275/40-20 and 295/40-20 -or- 315/35-20 in the rear when the time comes.

Should I install these wheels now or wait until I can get correct sized tires?

[TriX5]

Do NOT install, get correct rear tires first. You will damage transfer case with these rears. You need tires with matching circumference. Only the 315 is eligible. You might want them to be same brans and style.