But tires is easily measurable. It's pretty difficult to judge oil without a fair amount of expertise.
Most oils meet requirements to be considered 3-4 different viscosities anyway. A 5W-30 oil will sometimes cover everything from 0W-10->10W-40
08 WK Hemi: 4" Superlift, 305/55/20 Terra Grapplers, 20x9 KMC Misfits, Superchip, AirRaid Intake, Custom Exhaust, Custom Toolbox Mount, 4xG Rear Diff Guard, JKS Quick Disconnect, Rola Rack, KC Daylighters