@Opus 17 is correct that your employer is required to withhold taxes on a bonus that significant, regardless of whether they give you the cash or the car itself (if they give you the car, they're supposed to withhold based on its FMV).
But it would certainly be wise for you to talk to your payroll department to make certain they intend to do so. If they don't withhold, the one who's going to get socked with the tax bill is, of course, you.
The company can either withhold a flat 22% of the bonus, or they can "aggregate" the bonus amount with your regular salary and withhold according to your filing status and W-4. The latter is usually what's done.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
