My truck, tractor, and trailer are all used for both personal and business.
You need to log hours on your tractor, and miles on your truck. And save ALL receipts.
At the end of the year, they take the total miles (or hours on the tractor) and figure the percentage of personal and business use. IE: you put 1000hrs on the tractor and can document and show 600 hours was for business....thats 60%. You can then claim 60% of the expenses. Fuel, repairs, etc. Same for the truck.
Allthough if you use a truck, most just take a mileage deduction. Saves on receipts. The mileage is meant to cover your fuel, repairs, insurance, maintenance, etc. I have a big diesel truck. 90% of the time it is either plowing snow or towing the trailer for business. I have found that with fuel, tires, repairs, insurance, etc I have more expense than the mileage allows for. So I itemize and save all my receipts.
Also consider the other implications of depreciating the tractor. If you depreciate it, (i dont remember what the term is) but lets use 5 years. And lets assume you paid 25k for it. You can depreciate 5k per year. But at the end of the year, the tractor is worth -0- in the eyes of the IRS. Now if you sell it for $15k......You have to show that $15k as profit.