Adding weight to just the rear of a Bobcat makes to hard to drive anywhere but flat ground. I mounted a weight bracket to the rear of mine and just the weight of the bracket changed what inclines I can drive forward on with a empty bucket. I needed the extra lifting capacity to move some machinery around with the forks. The counterweights that Bobcat sells for some machines fit over the axle housings.Realistically it should be 1:1, but to stay on the safe side I would go .75:1 for the counterweights. Most Bobcat built machines are tail heavy anyhow vs a machine with the NH or JD design, so adding more weight to the the tail makes it tricky traversing hillsides.
You may alos want to consider filling your real tires with windshied washer anti freeze, though I'm not sure how many gallons they hold.Adding weight to just the rear of a Bobcat makes to hard to drive anywhere but flat ground. I mounted a weight bracket to the rear of mine and just the weight of the bracket changed what inclines I can drive forward on with a empty bucket. I needed the extra lifting capacity to move some machinery around with the forks. The counterweights that Bobcat sells for some machines fit over the axle housings.