You will have to provide a log book of miles driven if you ever get audited.
That is what we had to do for an IRS audit
You need a 'contemporaneous written record' which the IRS has long accepted as a printed copy of an electronic logger. There are many smartphone apps and many auto/truck GPS units that can record this when you specify the destination at the start.
One absolutely VITAL need is to record the vehicle odometer at year start and end. Everything else flows from that total miles!
There are many phone tracking programs that create your log.
Most people just keep a calander and write the mileage in the day.
I’ll take that back, most people keep their mileage log on my office ceiling. I ask them how many business miles they’ve driven and they look up and then give me a number!
A hard cover ‘account book’ LIVES on the front seat of both my vehicles. Along with a 3 ring binder with all info regarding title-registration-insurance-dog vaccinations (dog is always with me)—Horse ownership & registrations in truck that hauls them, etc.
Date of gas purchase—# of gallons & MPG—which tells me when I need a tuneup. Mileage goes down.
ALL other items-—adding oil—change oil/filter/air filter——adjust brakes—alignment—adjust steering box lash— change radiator fluid—new batteries—ANYTHING done to the vehicle is also recorded.
I still have those books back to 1980 when I became self employed doing accounting for a number of small businesses who never needed a full time bookkeeper.
Some records prior for my own info also still retained.
At one point, I had a 1965 Pontiac station wagon—1972 Honda 600 with motorcycle engine—1979 Buick station wagon—1976 Chevy 1 ton truck—1976 Navajo 2 horse straight load trailer.
Sold Honda first-—(39 mpg)—It couldn’t tow trailer.
Sold Pontiac next-—with OVER 444,000 miles on it-—guy restored exterior. Ran fine.
Sold 2 horse about 2012—had bought 4 horse in 2001. Still have 1 ton truck & Buick.