All other things equal, a heavily loaded engine is more efficient than a lightly loaded one. But tractors are not just engines. Weight has a huge effect on efficiency when we're talking about drawbar power. A small, light tractor is going to have more slippage than a heavy tractor with big tires. To compound matters, the smaller tractor may have to pull an implement at a lower speed than the big tractor. The slower the speed and the lower the gear ratio, the more power is lost to slippage.
In the example you give, pulling a four bottom plow with a typical 60 hp tractor is going to result in a lot of slippage. The 90 horse tractor is going to pull that plow easily and in a faster, more efficient gear. Of course, either tractor can run the hay rake, and the smaller tractor will do it using a bit less fuel. But on average, I'd say the bigger tractor is going to be more efficient.
Same-Day Shipping! Most of our stocked parts ship the same day you order (M-F). Expedited shipping available, just call! Most prices for parts and manuals are below our competitors. Compare our super low shipping rates! We have the parts you need to repair your tractor. We are a Company you can trust and have generous return policies! Shop Online Today or call our friendly sales staff toll free (800) 853-2651. [ More Info ]
TRADEMARK DISCLAIMER: Tradenames and Trademarks referred to within Yesterday's Tractor Co. products and within the Yesterday's Tractor Co. websites are the property of their respective trademark holders. None of these trademark holders are affiliated with Yesterday's Tractor Co., our products, or our website nor are we sponsored by them. John Deere and its logos are the registered trademarks of the John Deere Corporation. Agco, Agco Allis, White, Massey Ferguson and their logos are the registered trademarks of AGCO Corporation. Case, Case-IH, Farmall, International Harvester, New Holland and their logos are registered trademarks of CNH Global N.V.