front axle weight = how much of a load you put into the FEL (front end loader), after x amount of weight you could damage the front axle.
as your front axle weight goes up, the higher the PSI you want in the front tires, so you do not run the front tires flat and then run off the tire off the rim.
but the way you ask your question, it sounds like there is actual cast iron weight on the front axles? i suppose if FEL, came off tractor, you would want some sort of front weight to balance out tractor so you do not do a wheelie constantly with backhoe on. more so when backhoe gets used and needing counter balance weight on the front. but the FEL with bucket on should be enough counter weight. or less something unique for the tractor ? though for a TLB (tractor loader backhoe) having a FEL on generally is FEL and backhoe on at all times, and not designed for FEL or backhoe to not come off or less needing a major repair done on the tractor when speaking industrial equipment. agricultural equipment is a different story.