I smoke Beef Ribs every Saturday at my BBQ joint. Really one of the easiest meats to get great results.
Trim any really thick fat from the top of the rack (anything you don't think will render and anything you wouldn't want to eat if it didn't render), leaving about 1/8" fat layer. I don't remove the membrane on the bone side as it helps to keep the rack from falling apart. We season with S&P only. We smoke at 260 degrees, unwrapped for 3-6 hours until very probe tender. Every rack is different so even if one rack is done other racks may not be. Beef ribs should be VERY tender. Fall off the bone almost. I'm assuming that what you're cooking here are plate ribs - 3 bone racks. If your probe finds any tough areas in the rack, let 'em keep going. Make sure you rest them down to about 150 degrees before eating. Final product will be very moist and tender. Have fun.