The spare has about 20k fewer miles on it and clearly has more tread on it, maybe a quarter to half inch taller when side by side.
So how bad is it to rotate in to the mix at this point?
I know some cars are super sensitive to even small differences in tire sizes causing transfer case failures.

 

I wouldn't risk it. From what I've read, these Discos are some of them with more sensitive transfer cases and that's a LOT of tread difference.

 

You'll be fine. As long as you aren't running 3 - 33" tires and 1 - 31" or something drastic like that, don't lose sleep over it.

 

Not an issue.

 

Thats 2 to 1 for those keeping score. Bump for more

 

If Zack and Erik say yes, then I'm changing my answer to yes. Those two would know.

 

So it would be equally a non issue if i were to use a 255/65R16 for a spare when I get new tires which will be 245/75R16?

I'll probably eventually buy a new spare but in the mean time I won't kill my Tcase if I had to actually use the spare?

 

That would definitely be an issue. You are talking roughly a 1.5" difference at that point.

 

Thanks, Erik... I'll buy 5.

 

So how much difference is too much? I'm debating going out and measuring mine with paint and roll test.
How would I know if it was starting to cause a problem?
I'm on 275/65/16 Duratracs fwiw