Tractor traction was studied from 1960 to 1989, focusing on how well tractors can pull heavy loads. Four-wheel drive tractors have the best traction compared to other types. When used without extra weight, they can pull 3% more than front-wheel drive tractors in four-wheel drive mode. Front-wheel drive tractors pull 28% more in four-wheel drive mode than in two-wheel drive mode. Two-wheel drive tractors without extra weight pull 8% more than front-wheel drive tractors in two-wheel drive mode. Adding extra weight doesn't improve traction for front-wheel drive and two-wheel drive tractors, but it does increase how much they can pull. On concrete without extra weight, four-wheel drive tractors have the highest traction, followed by front-wheel drive in four-wheel drive mode, two-wheel drive, and front-wheel drive in two-wheel drive mode. Crawler tractors on flat, firm land without extra weight have the best traction overall.