The Crew - Salt Rocket - Achieve a speed over 236 mph (380 km/h) on the Bonneville Salt Flats. [Bronze / 15G]

You can only do this with two cars in the game! The RUF CTR-3 which can be bought at the Miami Car Dealer (costs $306,000 or 67,993 Crew Credits) and the Koenigsegg Agera R which can be bought at the Los Angeles Car Dealer (costs $1,107,000 or 245,975 Crew Credits). If you keep your 100,000 Crew Credits from the beginning of the game you can easily buy the RUF CTR-3 with it. You must use the Full Stock version of these cars to reach their speed limit (that's how you get the car when you buy it, without any tuning and without the performance spec equipped)!
The Bonneville Salt Flats are north of Las Vegas. You don't actually have to drive on the salt flats, only on the street(s) of this area. It takes around 2 miles (3km) to reach 236 mph, so start from Las Vegas and drive all the way up to the Salt Flats. Once the speedometer in the bottom left corner shows 236 mph or 380 km/h the trophy / achievement will unlock.