I use airsoft bb's. They are cheaper and quieter. I have them in everything from small quad tires all the way up to 40" mud tires. The ratio I have was for big tires but I have played around with weights and kind of have it figured out. You can have too little but it doesn't seem to hurt anything if you have too much weight. quad tires I use about .25-1.oz of bb's depending on height and width of tires. Never needed any in my motorcycles though. The ratio I was given is 35" tires use 5oz and for every inch taller add an oz. I think that is a little much. I have 2oz in my 33's and they run smooth as a Caddy. It's a good start point though.