I was told by Tirerack that 275/40/18 would be too tall for my rear. Is this true? I have 18x10 out back.

 

In the rear, I have a 275/35/19 and it fits perfectly.

 

No it wouldn't be too tall. It might not be wide enought for a 10" tire though. I have a 285, and wish I had a up to a 305. You can run a 275 on a 9" rim and be fine, but on a 10" rim it might look streched or not fat enough.