Best-selling games tend to have you firing big guns, fighting zombies, or driving through the mud in Russia.

Wait — what?

Developer Oovee Game Studios revealed today that it has sold 100,000 copies of Spintires. The truck-driving simulator debuted on Steam on June 13, which means it reached the 100,000 milestone in just 18 days. That’s impressive for a superrealistic driving simulator that has you guiding a mammoth Soviet truck through off-road trails, and it is evidence of the power that the PC digital-distribution service Steam has to lift smaller games.

“I am very proud that my company and my team have fulfilled the wishes of many — by producing a game for the off-roading genre,” Oovee managing director Zane Sexton said in a statement. “Clearly, this muddy adventure was a good choice and we will endeavor to improve the platform with free updates and DLC.”

Oovee and publisher Imgn.Pro are selling Spintires for $30 right now on Steam. It also has boxed copies in markets like Russia. The sim attracted attention immediately from fans of the hyper-realistic-driving genre, and that was enough to get it on Steam’s top-selling chart. Spintires quickly climbed to No. 1 on that list, where it remained for several days in a row. It is still on Steam’s top-10 best-selling list. That places it above major triple-A releases like Wolfenstein: The New Order and Watch Dogs.

“Spintires was one of our biggest projects,” Imgn.Pro cofounder Bartosz Moskała said in a statement. “Our goal was to elevate the game from indie to mainstream and to provide it with the best market visibility and complete global distribution solution. Although it’s just the beginning of the road, the numbers speak for themselves already.”

This isn’t the first offbeat game to perform well on Steam. Top sellers on the platform right now include unfinished games like Rust and Day Z, which are both part of the network’s Early Access program.

Oovee didn’t detail what kind of new downloadable content it has in the works, but it will likely introduce new maps and new vehicles.

Quick Look: Spintires