If it has the 15-19.5 tires, then Roy is right, my 790 took 30 gallons. With Rim Guard weighing approximately 11lbs per gallon, that is only an additional 660lbs. If it is like most tractors that are filled at the dealer today (or even the mobile independent fillers some use) it will have a mix of Methanol & Water, since methanol is lighter than water, you usually net around 7lbs. per gallon which is around an extra 420lbs. Around here, it costs on average $200 to have tires filled, so unless you are going to be saving $200 in fuel for not carrying the extra few hundred pounds, its probably not worth it to drain them. Not to mention, when you get to where you are going, you either have to take it somewhere or wait to have someone come to you to fill them before you have the convience of using a tractor with filled tires right away.