[neon_rt]

A good size of wheel is 16" on these vans. With 16" wheels you can use 235/55 -16 tires. These are low profile, maintain the correct diameter and are relatively inexpensive. If you want to go lower price you can use 225/60 - 16. Your speedometer will be off a little. You will be going 61-62 when your speedo reads 60. I usually use the 225/60 because there are a lot of tire choices ranging from $40 each to $200 each. With the 235/55's you will spend $100-$250 each with only three or four choices among all of the various brands. You can go to 17's but there is really no advantage of doing so and the tires are really expensive.
Another issue you may run into, is that Caravans that came with 14" wheels only have light duty 10" disc brakes. All others come with a standard duty 11" disc. When you put bigger tires/wheels on, it causes a lot more strain on your undersized brakes. I found that I no longer had enough brakes to lock up the tires even with two feet on the brake pedal. The brakes on these van stink anyway, they should not be allowed to put such feeble brakes on a Minivan.