Today I did a brake job on the rear. I noticed the left rear tire is going to need replacing as the tread bars are indicating wear. The two tires on the rear were of different manufactures. The right tire is an Arroyo Grand Sport A/S 255/35ZR19 96W and is in like new condition. (Only had car a couple months.) I can't find another Arroyo tire with the same numbers. The one that I can find is designated 255/35R19 XL 96W which is a higher weight bearing tire than what is currently on my car. Don't know what the "Z" means before the "R" for Radial inner construction. Will it make any difference to match the higher load tire "XL" with what's currently on my car? And what does the "Z" mean?