Well, in that case try and create a log for your records that matches what you are claiming on the tax return. The IRS looks at your profession as well as your historical miles driven as well.
Remember, the problem for outside sales consultants or taxpayers who use their car frequently for business travel is that they fail to maintain any kind of logs and when they estimate their miles for tax purposes it is generally lower than what the actual miles driven. At least try and maintain 1 months log and then you can extrapolate the 12 months assuming there is some consistency in your business mileage activity.
But, 40,000 miles is very large indeed! I think any CPA preparing your tax return is going to ask you for a vehicle log, just my guess! It would be a red flag item so it would be best to have a log when claiming these miles on your tax return.