I've recently had the misfortune of having a flat tire 3 times over the past 6 months in my LS. The most recent flat was a lovely piece of steel rebar that found itself burrowed into my rear passenger tire making it un-repairable. I had the original full size spare tire in decent condition and am currently using it while my spare tire is now replaced with a General Altimax RT43 255/45R19. Stock tire size is 245/45R19 but that size has more limited selection, most of which are on the pricier side - $225. The RT43 on the other hand was $135 with overall good to great reviews by Consumer Reports. Coupled with the fact that it was going to be my spare tire, I felt that so long as the tire would fit into the trunk well, I would be satisfied with my decision. Thankfully, it fits snugly and I have a future decision to consider whether to swap to 255/45R19s for my next set of 4 tires after 10k more miles.

A side note was that my original spare tire is now a little past 10 years old with 7/32 tread so I am wearing it down to replace along with my other tires. Age and tread are both factors when considering replacements.

 

(Strange that I'm writing two posts on tire profiles back to back). The overall diameter for the 245/45 tire is 703.1mm so it will rotate 751.42 times per mile, the 255/45 tire is 712.1mm and will rotate 741,92 per mile. So the 255 tire will show low on the speedo, 1.28% to be exact. Not a huge variance. Switching to something like 255/40 would reduce the diameter to 686.6mm and make the speedo 2.4% fast.

 

Hopefully your LS is not AWD. You absolutely cannot have two different size tires with the AWD system, so if you ever used that spare you would risk damage.

IMHO tires are really important. I would just buy a new set of 5 tires in the right size. I'd do it now too, I wouldnt ride on that old spare.

 

Good info to note. Thanks.