May you use actual expenses on a spare business vehicle that was purchased as a
backup for the other vehicle that uses standard mileage?
That is a really good question. My guess would be that as long as you adhere to the rules the IRS has set when it comes to deducting actual vehicle expenses that it would be fine. However, you will need to keep detailed records of when the spare car was used to prove that there is no overlap between the time you drove your primary vehicle versus when you drove the spare car for business. I would recommend that you consult with a tax professional who can look at your situation and offer guidance.
In addition, here are a couple of resources that might be helpful:
Thank you for reading!
All the Best-