EW! Those oven racks are gross.
Okay, so you are always careful to prevent spills in the oven. Maybe you put lids or aluminum foil over any food you're baking. Yet somehow we still find spills and splatters on our oven racks. Those black chunks of residue look pretty bad on the rack. What's worse is it's next to impossible to clean the racks without putting blood, sweat, and tears into the work. We have an answer to your woes!
The rack hack...
Take your oven racks out and place them into your bathtub or a plastic tub (if you have one that's big enough). Fill with hot water and add a spoonful or two of the powdered dishwasher detergent. Let the racks so for 20 minutes or so before you use a sponge/scratchpad to easily take the remaining residue off. Be sure to wear gloves so you don't get the detergent all over your hands.
While you're at it, run the self-cleaning oven feature. Now is the perfect time because you have to run this feature without the racks in the oven, as the intense heat will ruin the racks.