One of my customers has a nissan F05 rated for 13500lbs lift at 24" load center. They use a long boom attachment on the forks for lifting large sheets of stone, well below the capacity of the machine, if it were at the stated load center. They feel that its a little too bouncy and have started stacking sand bags on the back of the counter weight and in the process partialy blocked part of the radiators exhaust duct.

I think adding ballast in the steer tires would be a better solution. This is done frequently on farm tractors and construction equiptment, but I've never seen it on a forklift, is there any good reason not to do it? Any other ideas?
BTW The customer is not going to change the way they move thier materials or buy a bigger machine.