According to sources, 20w50 is thicker than 10w40. Since 10w40 is lighter, it can improve shifting and make neutral easier to find on a stubborn transmission.
Plain bearing clearances determine or control what weight oil a motor should have circulating through it; 20W50 is too thick for some modern high horsepower engines.
The bearing clearances have gotten tighter with the increase in horsepower output. Proper oil pressure all over the whole motor is crucial if you want your amped up sportbike to last. If the oil is too thick, particularly when cold, oil pressure drops.
From Auto Credit Express, one of the experts in the auto industry, Edmunds, released an article addressing the “Top 7 Urban Legends About Motor Oil”. Find out more here.