– Old favorites are getting new life under the Golden Arches.

Last month, McDonald's rolled out two new sizes of Big Macs — the Grand Mac and the Mac Jr. — and a few weeks ago, it added to its annual Shamrock Shake offer with four new mint-flavored drinks. Other riffs on menu staples are being offered in regions around the country, including the Sriracha Big Mac, garlic fries and Chicken McGriddles.

The strategy behind the introductions is a smart one if it works, observers say: It allows the world's largest burger chain to entice new customers and convince old ones to buy more, while keeping costs low and limiting complications in the kitchen.

"If you look at our past, we were probably too focused on leaning on new products," said Lance Richards, McDonald's vice president of menu strategy. "Now we're celebrating the menu items that are uniquely McDonald's. And we think there are huge opportunities to do more of that across the menu."

Since CEO Steve Easterbrook took the helm almost two years ago, the company has focused on improving the quality rather than the quantity of its menu items, but bringing more customers in the door has been a challenge.

McDonald's needs to entice more customers without going out on a limb to create a flashy new menu item that might not sell, said restaurant consultant Dan McGowan.

"A great hostess walks a step to a step-and-a-half in front of the guest. If they get three or four steps ahead, you'll have people standing around in the middle of the restaurant looking around saying, 'Where'd she go?,' " McGowan said. "It's the same thing with the menu. If you are three or four steps ahead, you might lose them."

Adding too many new menu items can also bog down a kitchen while workers get used to constructing a new sandwich or using new ingredients. "You don't want to give employees a whole new binder on how to assemble a sandwich," McGowan said. "They know how to make a Big Mac."

Timing is especially important at quick-service restaurants like McDonald's, which aim to deliver orders in less than two minutes and get most of their business from a drive-through.

When it comes to menu additions, "McDonald's is a little more sensitive [than other restaurants] because you have 70 percent of your customers coming through the drive-through," said John Gordon, principal at Pacific Management Consulting Group. "You can have a little bit of relaxed service times in the dining room, but if you're in the drive-through, things can get a little dicey."

With the Big Mac, McDonald's is hoping that adding more sizes will bring in more customers. McDonald's clientele tends to skew older, Gordon said, and the burger chain has had trouble luring millennials away from better burger rivals like Five Guys. By adding a snack size Mac Jr. for those lighter eaters and a Grand Mac with more meat for heftier appetites, McDonald's can entice a wider range of customers to try the sandwich that first came onto the menu 50 years ago. McDonald's has said the Mac Jr. and the Grand Mac are available for a limited time but it hasn't said how long they will last.