Formula 1's biggest stars can find out why it's called Sin City this weekend ... 'cause one Nevada brothel is opening its doors and offering each driver free sex ahead of the Las Vegas Grand Prix!!

TMZ Sports is told ... famous Chicken Ranch brothel workers Addison Gray and Alice Little are really excited to welcome the race to their home turf for the first time since 1982 ... and they want to make sure every driver leaves Vegas happy.

We're told the licensed sex workers are offering a special one-on-one session at no charge for all the guys on the grid ... just in case they want to see some action prior to Saturday's race.

"It’s Formula 1 fever in Las Vegas this month and we’re all psyched up for the big event," Little told us.

"Any driver that wants to get their hearts racing and celebrate the F1 with me and Addison will be treated to 100% complimentary coitus."

Drivers aren't the only ones gettin' perks -- Gray and Little said they're also giving a 50% off deal for anyone flocking to the desert for the festivities.

"Our discount will help Vegas visitors and residents blow off some steam with a couple of generous ladies so that they can chill out during race week," Little said.

"Everyone who made F1 in Vegas possible deserves a break, and we’re here to provide some well-oiled appreciation."

Gray said the Grand Prix also needs a little bit of spice anyway ... especially since they stopped using Grid Girls years ago.

"Since Formula 1 banned their fabulous grid girls in 2018, the events have been overwhelmingly lacking in much-needed sex appeal," Gray said.

"Our discount isn't just a gesture of love for F1; it's an invitation for fans to revel in an experience where sex appeal is celebrated, not sidelined. Because in our world, glamour isn't forbidden; it's the star of the show!"