Spare tire opinions

Recently I was at the dealer for my inspection/emission. After an oil leak caused by an over torqued drain bolt that broke the washer and leaked over a quart of oil on my driveway when the truck had 8k miles on it I started doing the other maintence myself.

My truck has 285/75R18 Wrangler Duratracs and I have the same size spare but in a different brand tire because I didn’t want a spare 3” smaller for obvious reasons. The dealer told me I’d trash the differential if I ever used that spare because it’s a different tread. I’d love to hear the forums opinion on this.

 

I can see how maybe a different sized tire might cause a problem, but I’ve never heard of a different tread pattern of a same-sized tire causing a problem with the diff. Did they explain why and how? FWIW, I’m running ATs, but my spare is an MT of roughly the same size, so this issue interests me as well.

 

Exactly, the size difference I knew already and makes total sense but unless I’m in 4x4 low on blacktop in the dry I can’t see a few miles on a different tread causing any problems.

 

Meh, more dealer gibberish from people who don't know anything. Ignore and move on.

 

Maybe the dealer installed a mechanical locker for you and didn't tell you they did it and now they're warning you about tires.

 

could be lol they’re generous like that