The wheels on the Tyler cart give it its 500 lb limit. They are rated at 250lbs each. The monster timbers I've wheeled around were Douglas Fir. On a concrete slab and graded gravel yard, going slow and avoiding potholes they groaned but performed nobly. You have to know the limits of any tool. Day in, day out the cart has proved itself to be extremely useful. It works great for 90% of the fir timbers I use. It's lightness and maneuverability save material handling hours. Also Picking the cart up with one hand and throwing it into the back of a truck to go to the job site is not such bad thing sometimes.