It's Gotham Girls posing on dirt bikes (or whatever they are). The concept is fairly cheesecakey. And yet, you know exactly who they are, what differentiates them, and they look like could possibly exist in reality.
Ivy and Harley aren't riding dirt bikes. Selina is riding a bar hopper.
"Fairly cheesecakey"? More like VERY cheesecakey. And good GOD, what is wrong with Harley's legs? Anatomy fail.
The girls looking, as you put it, as if they "could possibly exist in reality" may be for one of two reasons: One, there's a longstanding tradition of automobile and motorcycle manufacturers using women to sell their product. Two, the girls look like they're riding customized bar hoppers, etc. here, and there's the stereotype that women bikers (particularly Harley riders) are either thin and sunburned with bleached feathered hair or heavyset with huge busts. So Nguyen may be playing to that or poking fun at it.
Ivy on the dirt bike is the worst - because, yes, when you're riding a dirt bike, you don't protect your arms or legs.