When is the right time to drop collision coverage on an older car?

The formula I like to use is to calculate the value of your car now, then deduct the collision deductible from that amount.  This gives you the approximate amount you would receive in the event of a total loss to your car.  Now divide the amount of yearly collision insurance cost for that vehicle into this amount.  This will show you how many years you would have to go without a total loss to your car to break even.  If you feel you can go that long without totaling your car, then it is probably time to consider dropping the collision coverage on that vehicle.